AN INVESTIGATION OF THE EROSION TECHNIQUE
FOR THE EVALUATION OF PEDESTRIAN LEVEL WINDS
IN THE WIND TUNNEL
by
ROBERT ERIK /RIP
B. Arch.,
University
of Cincinnati
(1978)
Submitted to the Department of Civil Engineering
in Partial Fulfillment of the
Requirements for the Degree of
MASTER OF SCIENCE IN
CIVIL ENGINEERING
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
June 1982
0
Massachusetts Institute of Technology
1982
Signature of Author
Department ofCvingn 8I
Department of Civil Engineering, May 21, 1982
Certified by
Frank Durgin,hesis
Certified by
/
J.M.
Supervisor
BigsY Thesis Supervisor
Accepted by
Francois Morel
Chairman, Departmental Graduate Committee
Archivei
.. CA.'fiHJSETTSiNSTITUTE
j" T2-rI36.
.,,ll
-j
2 182
,n.ADI-C,
AN INVESTIGATION OF THE EROSION TECHNIQUE
FOR THE EVALUATION OF PEDESTRIAN LEVEL WINDS
IN THE WIND TUNNEL
by
ROBERT ERIK GRIP
Submitted to the Department of Civil Engineering
on May 21, 1982 in Partial Fulfillment of the
requirements for the Degree of Master of Science in
Civil Engineering
ABSTRACT
High rise buildings can cause high velocity winds near
the ground that are dangerous to pedestrians. The only
practical way to investigate such a situation is to test a
model of the building with its surroundings in the wind
tunnel. The Wright Brothers Wind Tunnel (WBWT) currently
uses two types of tests in its ground wind studies - the
hotwire anemometer test, and the wind erosion test.
The
hotwire test is quantitative and discrete with respect to
ground locations measured.
The wind. erosion test
is
semi-quantitative and continous with respect to ground
locations measured.
Quantitative data from the wind erosion type. of study
would be very useful. A simple building shape was tested in
the wind tunnel using both methods to obtain a relationship
between the two types of data. This relationship was then
verified using data from two typical commercial ground wind
studies.
A large amount of scatter was found in the correlation
between the hotwire and wind erosion tests. This scatter is
believed to be mainly due to errors caused by the hotwires
measuring the flow at a height considerably higher than the
particle layer used the the wind erosion tests.
Some
suggestions are then given for techniques to measure the
flow at he correct height.
The wind erosion technique shows promise for obtaining
quantitative ground winds data over large areas. Further
testing needs to be performed to determine the accuracy of
the technique.
Thesis Supervisors: Frank Durgin / J.M. Biggs
- 2 -
Acknowledgements
I would
guidance
like
and
to
thank
supervision
Mr.
Frank
Durgin
for
his
throughout
the
course
of this
David Burleigh,
Mr.
Mark
Jackson,
project.
I also thank Mr.
and
Mr.
Chris
Sherwood
for
their
assistance
production of the figures for this report.
Burleigh
and
Mr.
in
the
I also thank Mr.
Sherwood for their assistance during the
data taking portion of the project.
I am deeply appreciative of my wife, Mary Ann, who,
addition
to
in
assisting with the figures, encouraged me with
her love and support.
Finally, I thank the Lord for giving me the strength to
finish this work in the time alloted.
- 3 -
TABLE OF CONTENTS
Page No.
Abstract
2
Acknowledgements
3
Table of Contents
4
List of Tables
6
List of Figures
7
List of Symbols
12
1. Introduction
14
2. Description of Experimental Equipment
28
3. Calibration of Wind Tunnel Flow
3.1
Introduction
34
3.2
Velocity Gradient
34
3.3
Longitudinal Turbulence Intensity
36
3.4
Power Spectrum
36
4. The Experiment
4.1
Introduction
40
4.2
Wind Erosion Test
40
4.3
Hotwire Test
43
-
4 -
Table of Contents (cont.)
5. Analysis of Results
5.1
Introduction
49
5.2
Wind Erosion Test
49
5.3 Hotwire Test
56
6. Correlation with Other Tests
72
7. Conclusions
80
References
83
Tables
85
Figures
90
- 5 -
List of Tables
Page
3.1
Gradient Heights and Power Law Constants for
35
Varying Terrains, from Davenport [12]
5.1
Angle Between Contour and Direction of Flow
85
at the Ground Plane (Degrees)
5.2
Degree of Piling for Ground Wind Locations
66
6.1
University of Minnesota -
86
Contour Gradient
Velocities for Different Locations and Wind
Directions
6.2
City of Buffalo, NY -
Contour Gradient
Velocities for Different Locations and Wind
Directions
- 6 -
89
List of Figures
Page
1.
Dwelling
in Hyderabad,
India
1]
90
2.
Result of Velocity Gradient Flow Around Buildings
3.
Meteorological
4.
Schematic Diagram of Wright Brothers Wind Tunnel
93
5.
Schematic Diagram of Wind Tunnel Test Section
94
91
92
Gap
6a. Hotwire Stand at Gradient Height
95
6b. Wind Tunnel Test Section, Looking Upstream
7.
Particle Size and Shape
96
8.
Instrumentation - Hotwire Test
97
9.
Variation of Hotwire Measurement with Wind Direction
98
10.
Simulated Earth's Boundary Layer
99
11.
Longitudinal Turbulence Intensity
100
12.
Power Spectrum
101
13.
Wind Erosion Test
102
14.
Hotwire
103
15.
Typical Hotwire Signals
16.
Contours
17.
Contours -
18.
Contours - h=l.0,
= 45 Degrees
107
19.
Contours - h=l.0,
= 0 Degrees, Run 2
108
20.
Contours - h=l.0,
= 0 Degrees, Run 3
109
21.
Contours - h=0.25,
22.
Contours - h=0.5,
Test
- h=l.0,
h=l.0,
104
= 0 Degrees,
Run 1
9 = 22.5 Degrees
e
105
106
= 0 Degrees
= 0 Degrees
-
7
-
il
Page
- h=0.75,
8 = 0 Degrees
112
= 0 Degrees
113
e = 0 Degrees
114
= 0 Degrees
115
23.
Contours
24.
Contours - h=l.0,
25.
Contours
- h=1.25,
26.
Contours
- h=1.5,
27.
Distance
of Stagnation Point from Windward Face
28.
Scour Are a for Different Building Heights
117
29.
Scour Are a for Different Gradient Velocities
118
30.
Contours
- Vgrad = 20 mph,
= 0 Degrees
119
31.
Contours
- Vgrad = 25 mph,
e = 0 Degrees
120
32.
Contours
- Vgrad = 30 mph,
= 0 Degrees
121
33.
Contours. - Vgrad = 35 mph,
= 0 Degrees
122
34.
Contours -
8 = 0 Degrees
123
35.
Scour Are a for Different Wind Directions
36.
Contours
-
h=1.0,
= 22.5 Degrees
125
37.
Contours
=
h=l.0,
= 45 Degrees
126
38.
Contours -
39.
Hotwire Locations for Simple Shape Building
128
40.
Local Direction of Flow
129
41.
Average Velocity Coefficient Contours
130
42.
RMS Velocity Coefficient Contours
131
43.
60 Hertz Peak Velocity Coefficient Contours
132
44.
Peak Velocity Coefficients - Locations 1, 10
133
45.
Peak Velocity Coefficients - Locations 3,-12
134
46.
Peak Velocity Coefficients - Locations 4, 13
135
47.
Peak Velocity Coefficients - Locations 7, 16
136
48.
Coefficient of Variation - Peak Velocities
137
e
Vgrad = 40 mph,
Final Run
- 8 -
116
124
127
Page
49.
Velocity Coefficients - Locations 1-8
138
50.
Velocity Coefficients - Locations 10-17
139
51.
Velocity Coefficients - Locations 21-27
140
52.
Velocity Coefficients - Locations 31-37
141
53.
Velocity Coefficients - Locations 41-45
142
54.
Velocity Coefficients - Locations 51-55
143
55.
k Factor for Peak Velocities
144
56.
Coefficient of Variation - (peak - avg.)/RMS
145
57.
k Factor for Squares of Peak Velocities
146
58.
Angle Between Contour and Direction of Flow
147
59.
60 Hertz Peak Velocities for Different Angles
148
60.
Coefficient of Variation
-
k angle
149
61.
Coefficient of Variation
-
k pile
150
62.
Coefficient of Variation
-
k dist
151
63.
Variation of Peak Velocity with Gradient Velocity
152
64.
k Factor for Different Gradient Velocities
153
65.
Univ. of Minnesota - Existing Bldg. - North
154
66.
Univ. of Minnesota - Existing Bldg. - Northeast
155
67.
Univ, of Minnesota - Existing Bldg. - East
156
68.
Univ. of Minnesota - Existing Bldg.
69.
Univ. of Minnesota - Existing Bldg. - South
158
70.
Univ. of Minnesota - Existing Bldg. - Southwest
159
71.
Univ.of Minnesota - Existing Bldg. - West
160
72.
Univ.of Minnesota - Existing Bldg. - Northwest
161
73.
Univ. of Minnesota - Proposed Bldg. - North
162
74.
Univ.of Minnesota - Proposed Bldg. - Northeast
163
-9-
- Southeast
157
Page
75.
Univ.
of Minnesota - Proposed Bldg. - East
164
76.
Univ. of Minnesota - Proposed Bldg. - Southeast
165
77.
Univ. of Minnesota - Proposed Bldg. - South
166
78.
Univ. of Minnesota - Proposed Bldg. - Southwest
167
79.
Univ, of Minnesota - Proposed Bldg. - West
168
80.
Univ. of Minnesota - Proposed Bldg. - Northwest
169
81.
Univ. of Minnesota - k Factors
170
82.
Univ. of Minnesota - Peak Velocities
171
83.
Univ. of Minnesota - Normalized Peak Velocities
172
84.
Univ. of Minnesota - k Factors (extreme value)
173
85.
Univ. of'Minnesota - Peak Velocities (ex.,value)
174
86.
Univ. of Minn. - Norm. Peak Velocites (ex. value)
175
87.
City of Buffalo, NY - North
176
88.
City of Buffalo; NY - North Northeast
177
89.
City of Buffalo, NY - Northeast
178
90.
City of Buffalo, NY - East Northeast
179
91.
City of Buffalo, NY - East
180
92.
City of Buffalo, NTY
181
93.
City of Buffalo, NY - Southeast
182
94.
City of Buffalo, NY - South Southeast
183
95.
City of Buffalo, NY - South
184
96.
City of Buffalo, NY - South Southwest
185
97.
City of Buffalo, NY - Southwest
186
98.
City of Buffalo, NY - West Southwest
187
99.
City of Buffalo, NY - West
188
City of Buffalo, NY - West Northwest
189
100.
East Southeast
-
-
10 -
Page
101.
City of Buffalo, NY - Northwest
190
102.
City of Buffalo, NY - North Northwest
191
103.
City of Buffalo, NY -
k Factors
192
104.
City of Buffalo, NY -
Peak Velocities
193
105.
City of Buffalo, NY -
Normalized Peak Velocities
194
106.
Buffalo -
k Factors (extreme value)
195
107.
Buffalo -
Peak Velocities (extreme value)
196
108.
Buffalo -
Norm. Peak Velocities (ex. value)
197
109.
Omnidirectional Pressure Device for Measuring
Pedestrian Level Wind Speed [18]
-
11
-
198
List of Symbols
A0, Al
Hotwire calibration constants
D
Full scale characteristic dimension
d
Wind tunnel characteristic dimension
gr.
Grams
h
Height of simple building shape (feet),
or height in inches above tunnel floor
(Section
2)
hg
Gradient height
k
(peak - average)/ RMS
L
Constant
(feet)
Lx
Constant
(feet)
mm.
Millimeters
mph
Miles per hour
n
Frequency,
or number of groups of data taken by
power spectral density computer program
S(n)
Power spectral density function
T
Full scale time period
t
Wind tunnel time period
u
Full scale velocity
ug
Gradient velocity
ul
Velocity one foot above tunnel floor
uwt
General wind tunnel velocity
V
Full scale velocity
v
Wind tunnel velocity
Vgrad
Wind tunnel gradient velocity
- 12
-
Vwt
Hotwire voltage
v33
Full scale velocity at height of 33 feet
i<
Velocity gradient power law constant
X
nL/V33 - Nondimensionalized frequency
WC
Filtering frequency
Wind direction (degrees)
GI
RMS (Root-Mean-Square)
- 13
-
1.
Introduction
The
effect. of
structures
quite
wind
on
structures
and
groups
has been a concern of designers of buildings for
some
literature
time.
of
There
cases
are
numerous
examples
the
dwellings
One
scoops on the roof (Figure 1),[1).
larger scale is the design
which
the
the
example
in Hyderabad, India that are designed to
cause a flow through the interior of the dwelling
of
in
in which the wind played an important
factor in the design of the built environment.
is
of
streets
were
of
means
Another example on a
colonial
oriented
by
so
Buenos
Aires,
in
that the y were not
parallel to the prevailing winds [1].
The advent of the high-rise building has brought a
dimension
to
the
subject
After some of the taller of
of
wind
the
new
effects on buildings.
high-rise
buildings
were
built, it was noticed that the winds often reached very high
velocities at the ground level near the building.
times
were
so
at
severe that they caused pedestrians to lose
their balance while walking on the building
in
Winds
site.
Whereas
the past, this situation was caused only by the presence
of severe storms, today a high-rise
dangerous
gusts
when
the
building
can
generate
general weather is moderate, or
even if there is a gentle breeze.
The reason high-rise buildings
behavior
is
related
to
the
- 14
fact
-
exhibit
that
this
the
sort
of
Earth has a
.air
a
The Earth's boundary layer is
boundary layer.
of
layer
of varying height, typically 1000 to 2000 feet, through
at
zero
which the average velocity of the wind varies from
the ground to a gradient velocity at the top of the boundary
surface
the
of
surface.
Earth's
Above the
wind.
Before the construction of high-rise
little
buildings, the earth's boundary layer had relatively
the
on
impact
near
environment
wind
the
of
high-rise building allows the possibility
wind
velocity
higher
on
impinging
pressure to
be
height
with
bringing
the
portion
upper
the
gradient
velocity
of
the
the building, with a comparatively lower
pressure developed on
gradient
The
causes a high dynamic
building
on
developed
of
face
windward
a
instance,
high-rise
a
ground.
top of the building down to
the
at
For
level.
pedestrian
by
unaffected
relatively
gradient height, the velocity is
the
the
to
presents
earth
textured
rough,
It is caused by the resistance the
layer.
the
lower
portion.
a
downward
causes
windward face of the building.
This
near
the
reaches
the
flow
When this flow
pressure
ground plane, high velocities result.
A typical example of this
2.
Figure
On
stagnation
point
velocity.
For
the
at
which
over
the
the
depicted
in
building,
a
is
there
no
wind
boundary layer flow conditions, all the air
the
approaching the building above
pass
of
face
windward
develops
is
phenomenon
building,
while
- 15
-
stagnation
the
air
point
will
approaching the
building to the right and left will go around
to
the
right
and
approaching t
directed
left
sides,
the
respectively.
building
The
air
building below the stagnation point will
downward
toward the ground plane.
be
This situation
results in a vortex being formed in front of
the
building.
Thus, immediately in front of the building, the direction of
flow is opposite from the direction of the flow at
height.
The
air
in this vortex flow eventually makes its
way toward the sides of the building, and flows
corner.
around
the
The result is vortices originating from the each of
the two forward corners of the building.
ground
gradient
plane,
these
vortices
form
In the area of the
signatures
of
wind
velocity that are much higher than the velocity would be
if
the building were not present.
When designing large structures
structure,
it
If
situation
can
pedestrians
as
or
the
a
ground
there
will
be
a
wind
ground
which
injured
creates
by
the
loosing
problem
is
or financial success of a project.
for
the
wind
possibility
their
not
accurate
[2],[3].
Even
enough
to be
severe
- 16
-
aesthetic
For these reasons a need
prediction
velocities at a given project.
of
balance and
dangerous, it may be serious enough to impair the
has arisen
high-rise
velocity near the ground is amplified, a
result
being
not
falling as a result of high wind velocities
if
a
is neccessary to predict with some degree of
accuracy, whether
problem.
such
of
ground
wind
a
If the situation to be analized consisted of
building set in the middle of a clear field, it might
·block
be
single
to
possible
velocities
predict
analyticaly
a
around
Even
building.
complex building shapes,
it
is
the
ground
wind
for
somewhat
more
analytically
possible
to
obtain a relatively good idea of the range of velocities one
might expect.
the
that
However, it has been found
ground
environment around a building is very sensitive to the
wind
surounding
environment,
comparable
size.
as
such
It has also been found that the effect of
environment
the surounding buildings on the ground wind
difficult,
very
of
buildings
adjacent
if
impossible,
not
current state of the art of
predict with the
to
analytical
is
Since
techniques.
those techniques at present are unsuitable, investigators in
structures
the field have resorted to testing buildings and
in the wind tunnel.
The method that is generally used
scale
model
is
to
construct
a
of the building and its surroundings and mount
it on a turntable in the test section of
the
wind
tunnel.
The scale of the model has to be chosen such that (1) it can
fit in the tunnel test section and have a blockage
than
less
area
5 percent, and (2) the scale of the gusts in the
simulated earth's boundary layer are within a factor of
of
the
correct
scale.
on
two
Model scales ranging from 1:300 to
1:600 are common scales used in
model
of
practice.
Installing
the
a turntable that can be rotated allows testing of
- 17
-
the building in more than one wind direction convieniently.
When testing a model at
mentioned
a-"ve,
appropriate
parameters
(1)
the
flow
are
velocity
and
needs
similarity
that
intensity,
one
model
be
like
the
concerned
parameters.
The
with
ones
the
similarity
currently matched in practice are the
gradient,
(3)
to
scales
(2)
longitudinal
power spectrum.
turbulence
These flow similarity
parameters are discussed in more detail in Section 3.
To obtain data from the wind tunnel applicable
to
the
full scale situation, either the speed in the tunnel must be
decreased, or the time must be accelerated.
is
easier
to treat the gradient velocity as a constant and
increase the rate that data is
other
In practice, it
words,
taken
in
the
tunnel.
In
if the model scale is 1:400, all phenomena of
the flow is scaled down by a factor of
400,
which
implies
that everything occurs 400 times faster than it does at full
scale.
This is implied by Taylor's hypothesis [4] that
characteristic
lengths
of
gusts
in
the
tunnel
altered by the gradient velocity in the wind tunnel
following relation is observed:
(nD)/v = constant
where
n = frequency
D = characteristic dimension
v = velocity
- 18
-
the
are not
if
the
This type of test
number
effects
is
relatively
because
(1)
insensitive
Reynolds
boundary
layer
flow is
already turbulent, and (2) bluff bodies with
sharp
corners
such
unaffected
as
building
Reynolds
number.
velocity
in
the
shapes
The
the
to
are
main
tunnel
relatively
factor
and
governing
by
gradient
sampling rate is the maximum
speed at which the instrumentation can sample the data.
There are many types of wind tunnel tests that
conducted.
The
can
be
appropriateness of a given test depends on
the finances the sponsor has available for testing, and
the
type and degree of accuracy/ reliability of the data that is
desired.
of
the
Beranek and H.
various
types
Von Koten have compiled a
of
tests available [5].
divided the tests into three
yield
data
at
discrete
categories:
points,
(2)
which
They have
(1)
tests
which
tests
which
yield
continuous data over an area of the ground
tests
summary
plane,
and
(3)
yield continous data in the vertical direction
as well.
The instrumentation used for
first
category
are
the
tests
such
techniques
as
sand
visualization using oils, etc.
yields
some
ground
plane.
information
The
in
the
optical dynanometer, the hot wire
anenometer, the termistor, and tufts.
includes
mentioned
on
surface
-
19
The
second
erosion,
The sand
surface flow
erosion
gusts
and
flow
visualization
-
category
technique
turbulence on the
yields
information on the direction of flow at the ground plane.
The third category includes those methods
in
which
material is introduced into the flow that is visible.
a
Smoke
and soap bubbles are two examples of such materials.
All of these methods can be classified as to
of
data
the
type
that is being collected, i.e., either quantitative
or qualitative.
Tests such as the smoke, soap bubble,
sand
erosion,
surface
yield
good
to
gain
and
qualitative
data
and
flow
visualization
enable
the
investigator
important insights into the structure of the flow around the
building.
Tests
quanititative
using
data,
a
but
hot
it
wire
may
be
anenometer
difficult
yield
to obtain
insight into what is really going on from hotwire data.
Generally, most owners of tall buildings
desire
their
data in the form of an exceedance velocity associated with a
given probability,
interpret.
For
because
a
single
number
is
easy
to
example, a common measure for the velocity
at a given location on a site is the velocity that
will
be
exceeded two percent of the time.
One thing that must be considered when calculating such
an
exceedance
velocity
is
that
at
different geographic
locations, the probability that the wind will blow from
direction
direction.
is
generally
The
problem
one
not equal to that for another wind
becomes
- 20
-
how
to
handle
the
itself in the analysis of the
weather
the
of
variability
The
.ground wind environment for a building.
the
analize
weather
statistically.
to
The justification for
Der
Van
this procedure is contained in
is
answer
which he shows there is a spectral "gap"
paper
Hoven's
in
6] (see Figure 3).
He analyised data from Brookhaven, L.I., N.Y., as a function
of
noticed
and
frequency,
that there was a gap in energy
The
between a period of 5 hours and a period of 5 minutes.
peaks
major
in the spectrum occur at 1 year, and somewhere
one
in the vicinity of
at
occur
4-6 days,
minute.
Other
and 12 hours.
that the 1
It is obvious
year peak is due to the yearly progression of
seasons,
storms
day peak is the most common period for anti-cyclonic
in
and
The 4 to 6
12 hour peak is related to the daily cycle.
the
peaks
significant
the temperate region of the globe, and may possibly vary
geographically.
discussed,
due
peak
11-year
The presence of an
with
the
surface
frequency
pereviously
peaks
larger
the
discussed.
is
de-coupled.
hour,
1
what
scale
spectral
allows the two halves of the spectrum to be
Since weather data is commonly taken
hour
the
(Note that a
high frequency implies small sizes of gusts.) This
"gap"
of
of the earth,-and has a relatively
small scale high frequency compared with
low
also
The one-minute
to the 22-year solar cycle.
peak is due to turbulence caused by the interaction
wind
is
is
a
meteorlogical spectrum.
convienient
place
to
once
per
divide
the
All phenomena occuring with periods
- 21
-
greater
than
one
are
hour
periods shorter than one hour
tunnel.
Since
handled
are
statistically, while
simulated
in
the
wind
is little energy occuring at 1 hour,
there
out
with
Other topics that must be considered are (1) what
wind
phenomena occuring around this period can be left
little loss of accuracy.
velocities
these
affect pedestrians, and (2) how gusting modifies
Many
effects.
have
and
[2],[3],[7],[8],[9
problem
examined
have
investigators
this
various
suggested
criteria.
S.
Murakami, K.
Uehara,
and
Deguchi
K.
[2]
have
recently conducted tests of over 2000 pedestrians in an area
near the base of a high-rise building and have proposed
following
where
criteria
u
the
is the wind velocity averaged
over 3 seconds:
u < 5 m/s
no effect
5 < u < 10
some
effect
10
<
u < 15
serious
15
<
u
very serious
effect
effect
Other investigators have agreed that it is the 2
second
gusts
that
have
the
most
to
effect on pedestrians.
Pedestrians react to gusts lasting longer than 3 seconds
if
they
were
sustained,
high
average velocities.
significantly shorter than 1 second have not
to be dangerous.
- 22 -
3
enough
as
Gusts
energy
Assuming that a 3-second gust is to be modeled, and the
model
scale is 1:400, the sample size and sampling rate are
given by the following relation:
vt/d = VT/D
where
v = wind tunnel velocity
t = time in wind tunnel
d = characteristic wind tunnel dimension
V = full-scale velocity
T = full-scale time period
D = characteristic full-scale dimension
In this case, d=l,' D=400,
value
T=3600
seconds
(1
hour).
The
of V, obtained from the statistical weather analysis,
is typically about 20 mph.
Substituting into the
the sampling length t is found to be 9 seconds.
relation,
To find the
time period in the tunnel corresponding to a full scale time
of
3 seconds to model the gusts, the value of T is set to 3
seconds.
the
This gives a value of t =
appropriate
phenomena
that
.0075
needs
seconds.
to
be
Thus,
modeled is
technically feasible.
The
techniques
Wright
in
Brothers
its
Wind
ground
Tunnel
winds
techniques mentioned above, two are
are
the
hotwire
has
studies
used
[10].
currently
used.
various
Of
the
They
anenometer test and a modified version of
the sand erosion test.
- 23
-
Although the hotwire test suffers from the disadvantage
of
only
point
coverage,
it
has
yields quanitative data that can
an advantage in that it
easily
be
combined
with
weather data to obtain exceedance velocities associated with
a certain probability at discrete
Most
clients
require
this
locations
sort
of
on
the
site.
quantitative
data.
Therefore, the hotwire test is commonly used.
The disadvantage of the hotwire test is related to
large
the
amount of laboratory time that is consumed during the
aquisition of data.
Also, since the hotwire only takes data
at discrete points, it is necessary to sample as many points
as possible within the time constraints of the study.
tends
to
make
expensive.
what
the
a
hotwire
ground
wind
study
relatively
Furthermore, although the investigator can guess
ground
winds are doing between the points, it is
often difficult to guess accurately since the
conditions
boundary
This
are
so
complex.
conditions
configuation)
(a
general
flow
Often, a small change in the
minor
change
in
the
building
can significantly change the structure of the
flow.
The other type of test is a modification
erosion
Brothers
test
described by Van Koten [5].
Wind
incorporates
Tunnel
a
is
a
mechanical
closed
balance
or
any
the
sand
Since the Wright
return
tunnel
and
for the measurement of
forces and moments on aircraft, it was decided
sand
of
not
to
use
other hard substance that could get caught in
- 24
-
the moving parts of the balance or
would
accelerate
For this
motor.
These
elements
wear and greatly reduce the life of both.
reason,
plastic
particles
were
chosen
as
the
The procedure for this type of test is to sprinkle
the
material instead of sand.
particles uniformly on the ground surface of the model while
there is no wind, and increase the wind by
the
wind
increments.
As
increases, areas form on the ground surface where
the particles have blown away.
As
the
increases, these clear area(s) increase.
gradient
velocity
The areas with and
without particles are quite distinct - therefore, lines
easily
be
drawn
from
drawn separating the two areas.
data
obtained
from
the
can
Using the lines
different
gradient
velocities, contours can be drawn.
There are a number of
One
advantage
is
that
advantages
it
to
this
technique.
yields continous data over the
surface of the ground plane, in contrast to the hotwire type
of
study.
Therefore, the erosion technique may be used to
detect peculiarities that might go un-noticed in
study due to of the discretization.
a
hotwire
For this reason, before
conducting a hotwire test, this lab conducts an erosion test
to
aid
in
the
hotwire study.
selection
of ground wind stations for the
Another advantage is that the technique
be used to acquire data for very large areas.
impractical with a hotwire study.
to
test
whole
- 25
-
That would be
It now becomes
sections of cities.
can
practical
To date, this has been
done for two cities.
The third advantage is
that
the
test
is
relatively
economical in terms of wind tunnel time consumed.
The fourth, and not unsignificant,
the technique is visual.
advantage
is
that
This is important since people not
technically trained in the field can observe an erosion test
and
gain an understanding of the structure of ground winds.
Also, they are able to see the applicability of the test
to
the full-scale situation.
The main disadvantage of this technique is that it does
not
give quanitative data that can be combined with weather
data to obtain exceedance wind velocities.
present
only
yields
relative
The technique at
semi-quanitative
allows the wind environment at one location to
to another location for one wind direction.
be
any,
is
compared
exactly
being measured by the granule erosion test.
is unknown what quanity, if
It
In addition, in
contrast to the hotwire data, one is not sure
is
data.
constant
what
That is, it
along
each
contour.
The purpose of the test described in the following four
sections
was
to investigate what, if anything, is constant
along the contours, and to see if this
helpful
in
using
quantitative manner.
information
the
data
This
from
an
information
erosion
investigation
may
can
test
also
be
in a
yield
that would indicate changes in the procedure in
- 26
-
the
erosion
test
which
quantitative
data
obtained
would
improve
from it.
accuracy
in
It may also be shown
that a combined techique, involving the results of both
hotwire
and
erosion
test,
may
prove
estimating the ground wind environment.
- 27
-
the
more
the
effective in
2.
Description of Experimental Equipment
The Wright Brothers Wind Tunnel
return
wind
tunnel
is
a
closed
section
with a 7.5 x 10.0 foot elliptical test
section approximately 15 feet long (Figure 4).
Wind
speeds
of up to 165 mph are possible.
For aerodynamic tests such as the one described in this
thesis,
a
special floor is mounted in the test section one
foot above the regular floor of the
tunnel,
and
extending
two feet into the contraction section and four feet into the
diffuser (Figure 5).
flat
plane
the earth.
This floor increases the width of
the
that can be used to model the ground surface of
The floor is eight feet wide throughout the test
section.
To
model
roughness
the
blocks
earth's
have
boundary
layer,
at
and
been added to the floor (Figure 6).
The spires are specially shaped pieces of
vertically
spires
plywood
attached
the leading edge of the ground plane.
These
spires provide a velocity gradient in the test section.
flow
of
air
is
essentially undisturbed at the top of the
test section, and decreases according to a power law to
ground plane.
the
For different model scales, different sets of
spires are used, to model different scales
boundary
The
layer.
This
test
used
scale boundary layer.
- 28
-
of
the
earth's
spires to model a 1:400
To provide the correct amount of
ground
plane
turbulence
near
the
in addition to that provided by the spires, a
series of roughness blocks are attached to the ground plane.
The blocks start from about six inches behind the spires and
extend a distance of twelve feet.
each
measure
1.5 inches square and 2.0 inches high and are
oriented so that the
parallel
The roughness blocks each
and
faces
of
the
blocks
are
perpendicular with the wind tunnel flow.
The
blocks are positioned on a 4 inch
other
block
roughness
absent.
It
has
square
grid
with
every
been found in the past that
inserting a 2x4 piece of wood immediately behind the
spires
increases both the turbulence intensity and gust size.
Downstream from the roughness blocks
is
a
turntable.
The center of the turntable is positioned 16 feet behind the
plane of the spires, and is 6 inches to the left of
center.
The turntable is five feet in diameter, and is marked off in
feet, to increments of 1/20th of a
marking
the
turntable
foot.
This
method
of
is very convenient for interpreting
photographic wind tunnel data to the full
scale
situation,
since they differ only by a factor of the model scale.
During
special
the
hot-wire' tests
hardware
to
be
described
later,
was mounted next to the turntable to hold
the hot-wires during acquisition of data.
For
building
this
test,
was
affixed
a
model
to
the
- 29
-
of
a
generic
turntable.
The
rectangular
model was
positioned at the center of the turntable
and
so
oriented
the sides of the building were parallel with the x and
that
the
y axes of the markings on
constructed
of
was
model
It
to be a square in plan, 0.5 feet to a side.
was also constructed
heights
The
turntable.
0.25,
in
six
allowing
sections,
building
.75, 1.0, 1.25, and 1.5 feet to be
0.5,
modeled (i.e., range of height-to-width ratios of 1/2 to 3).
was
Care
to insure that the corners of the mode-l as
taken
tested were as sharp as possible to
insure
that
separated at the corners of the building.
became
The error
in the constructed model is such that with all six
assembled,
the
error
of
any
is
dimension
flow
the
sections
0.01 inches.
the
During the hot-wire test, the hardware was installed on
top of the model to hold one of the hot-wire anenometers.
Behind the turntable, at the end of
four
feet
into
the
granules
The screen is 1.5 feet high
width of the test section.
and
extends
more
tests.
closely
across
Although the catcher screen
was not needed for the hotwire study, it was left
to
used
erosion test as they are swept off the model by the
the
air flow.
the
plane
the diffuser, is mounted a catcher screen.
This screen is designed to catch the plastic
in
ground
in
place
approximate identical conditions for both
The granules caught by the catcher screen are
saved
for later re-use.
The plastic granules used in this test
-
30 -
were
available
in
a
the
variety
of colors, allowing maximum contrast between
particle
attained.
and
The
different
shape
of
ground
a
boards/models
typical
between
195-200
particles
specific density of about
be
particle is shown in
Figure 7 and measures approximately 1.5 x 2 x 2
are
to
mm.
There
1.07
per gram, givng an average
gr./cc.
Appoximately
one
particle in every 90 was oversized.
For the wind erosion test, an Olympus OM-1
with
an
automatic
rewind
was
mounted
5
SLR
camera
feet
over and
slightly off-center of the turntable to record the
results.
Kodak
ASA-400
print
film
was used in this camera.
Three
Lowel Tota-light lamps were mounted from the ceiling of
the
wind tunnel to provide illumination during the erosion test.
A pitot static probe located 15 inches below the tunnel
ceiling
and
in the vertical plane of the model was used to
measure the tunnel gradient velocity.
pitot
The
tubes
from
and static taps were conected to an alcohol manometer
and pressure transducer/ digital voltmeter setup to
the
the
velocity.
Presure Meter.
The
pressure
transducer
The digital voltmeter is a
was
a
measure
Baratron
Digitek
268
DC
Millivoltmeter.
The hotwire anenometers used in the test were
as
described
in
references
[10]
and
[11].
to
0.2
inches
modified
The hotwire
extended from a height
of
turntable
a typical scale of 1:400, this would
floor.
At
0.1
- 31
-
above
the
correspond to a full scale elevation of 3.5 feet to 6.5 feet
above the ground surface.
A Flow Corporation hotwire setup (900-1) and linearizer
were
(900-3)
used to make the voltage measurements (Figure
8).
To hold the hotwires when they are being calibrated
gradient
height, a stand was installed which hangs from the
wind tunnel ceiling (Figure 6).
increase
in
photographic
To
for
account
partially
drag this would cause, and the corresponding
increased
the
at
lamps
gradient
at
velocity
that
height,
one
the
of
was used in the erosion study was
removed.
is
Since the velocity that is measured by the hotwires
direction
(see
dependent
Figure
it is necessary to
9),
measure the direction of the flow at the location
is measuring.
hotwire
This is accomplished by using a thin
the
thread
positioned near the measurement location,
the thread will point parallel to
Great
accuracy
is
not
required,
the
direction
since
the
flow.
of
is
hotwire
relatively insensitive to errors in direction of up
degrees.
end.
the
metal rod with a thin flexible string attached to
With
the
that
to
+40
However, in gusting flow with high turbulence near
a stagnation point, the hotwire results can be annomalous.
- 32
-
As
noted
periods
earlier,
smaller
than
Murakami
at
filter
with
eliminate
seconds full scale.
filters
were
gusts
To
used,
one
Oscilliscope was used.
to
WBWT
filter
is
gusts
to
periods
the
for
monitor the readings from the
it is necessary
that
with
2 seconds do not affect pedestrians.
Thus, the procedure followed
to
found
introduce
shorter
data,
two
a
than 2
Krohn-hite
each hotwire (Figure 8).
hotwires,
a
Tektronix
To
5301
Since the hotwires are very fragile,
often
check
whether
they
are
still
operational.
All
PDP-11/20
data
computer
specified rate.
used
data.
to
was
measured
to
using
digitally
program
sample
HOTWI2
on
a
data
at
a
the
An ADll1-K analog to digital
converter
was
convert the voltage from the linearizer to digital
A DRll-C-was used to
interface
computer.
- 33
-
with
the
PDP-11/20
3.
Calibration of Wind Tunnel Flow
3.1 Introduction
earth's
boundary
certain
scaling
Proper wind tunnel simulation of the
relationships.
are
(1)
The similarity parameters to
with
gradient
velocity
intensity
turbulence
and (3) longitudinal velocity power spectrum.
height,
of
Scaling on the basis
in
represents
parameters
these
state-of-the-art
current
considered
be
height, (2) variation of
(RMS)
longitudinal root-mean-squared
with
of
consideration
requires
layer
the
structures in the earth's boundary
wind
the
testing of
tunnel
The following is
layer.
a discussion of each of these parameters.
3.2 Velocity gradient with height
The variation of
parameter
easiest
while
layer
significantly
velocity
to simulate.
the
exist,
better
height
with
than
that
overall
given
relation:
(u/ug) = (h/hg)
where:
u = average wind velocity at height h
ug= average wind velocity at full scale
gradient height hg
- 34 -
is
the
Davenport [12) states that
to
approximations
sophisticated
more
boundary
mean
the
accuracy
by
the
earth's
is
not
following
o< = power law constant, typically varies
from
.17 to .40
Davenport further shows that ug, hg and o< vary approximately
with the terrain, as given in the following table:
Gradient Heights and Power Law Constants for
Table 3.1
Varying Terrains, from Davenport 12]
Gradient Height,
hg (feet)
Terrain Types
Open field or water
*Wooded and suburban areas
Built-up Urban Areas
Exponent,
on
900
.16
1300
.28
1700
.40
The boundary layer used for this test had an hg =
inches
and
'=
.284.
43.5
For a model scale equal to 1:400, hg
This value is within the range
would be equal to 1450 feet.
of typical values given in Table 3.1 for a suburban boundary
layer.
the
Figure 10 depicts the velocity gradient measured
centerline
of
the
at
wind tunnel and 14 feet behind the
plane of the spires.
- 35
-
3.3 Longitudinal Turbulence Intensity
The longitudinal
(RMS)
mean-square
turbulence
variation
It is a
average velocity.
the
measure
is
the
about
velocity
of
the
root-
total
the
gusting
In Figure 11 the ratio of longitudinal
in the flow.
energy
of
intensity
turbulence intensity to the wind tunnel gradient velocity is
compared
with
full
similar
scale measurements.
scale measurements are from two locations, Sale,
and
Brokkhaven,
NY,
USA.
Sale
feet
.
Brookhaven
is
Australia,
is considered to be open
terrain, and has been assigned values of Co4=
900
considered
.16,
to
=
1300
feet
131.
hg=
.28
and
Since this data represents only two
locations, and the data was taken in
it
and
be typical of
suburban areas and has been assigned values of c<=
hg
The full
adiabatic
conditions,
is to be compared with wind tunnel data for general, not
exact agreement.
The longitudinal turbulence data taken for
this test were taken at gradient velocity of about 60 mph.
3.4 Power Spectrum
To
velocity
obtain
the
component
power
spectrum
of
the
longitudinal
for the simulated flow described above,
the wind velocity (measured by a hotwire) was sampled
program TWOSPC on WBWT's PDPll/20 computer.
plotted in Figure 12.
sampling
rate,
passes
The program samples
the
data
through
The spectrum is
at
a
a
specified
Fast Fourier
Tranform, and outputs the values of the power specrum.
- 36 -
using
The
voltage
from
the
hot
wire
was
filtered
at the Nyquist
frequency with a resistor capacitor network to minimize
effect
of
aliasing.
Since
the
measured
the
spectra are so
variable, the program allows the user to sample the data
n groups, and generates n
in
power spectral density functions.
The presented data is the average of the n groups.
In
this
case, n=16.
The shape of the spectrum is
with
the
in
one proposed by Davenport
reasonable
12].
agreement
This spectrum is
defined by the equation:
n s(n)
2
2
X
3
where:
4/3
(1+
2)
X = nL/V33
S(n)= power spectral density function
n = frequency
v33= average wind velocity at 33 feet full scale
L=1000 to 8000 feet
0-
=
RMS of fluctuating wind velocity
In this test, since the model is of a generic
shape,
the
scale
factor
is
Davenport's spectrum can be
factors that
would
not
used
a
to
building
fixed value.
ascertain
Hence,
the
scale
apply to the results of this test.
The
accepted value of L ranges from 1000 feet to 8000 feet, with
a typical
value
being
freauencv end of the
setting
L=3000
3000 feet.
spectrum with
feet,
By fitting
Davenport's
the
higher
curve
and
a scale factor of 1:400 is obtained.
- 37
-
Similarly, the acceptable range of
scale
factors
is
from
about 1:85 to 1:1600.
The power spectrum obtained in the wind tunnel can also
be
compared
to
proposed by Von Karman, given by the
that
following relation:
n S(n)
2
X
25/6
(l+kX2)
where
a
=
RMS of fluctuating wind velocity
S(n)
=
power spectral density function
n
=
frequency of velocity fluctuations
u 33
=
average wind velocity at 33 feet (10 meters)
L
-
3000 feet
X
=
nL/u 3 3
To compare this
necessary
to
2.
x
for Davenport, = n/u
spectrum
an
set
with
33
Davenport's,
equivalence
spectrum with the Davenport spectrum.
to set the peaks
Another
of
spectum
each
equal
is
first
Different
the
Von
One method is
to
each
other.
way is to set the values of the two functions equal
infinity.
The
in Figure 12.
With
to each other as the frequency n approaches
second
it
appropriate value for Lx.
authors have chosen different ways to
Karman
for Von Karman
method
is
the
one
presented
L=3000 feet and m=400, Lx=434 feet.
The data for the wind tunnel power spectrum
-
38 -
was
taken
at a height of 12 inches above the ground plane.
of
this
1:400,
According
to
corresponds
full
feet
much
14].
of
the
boundary
a
layer
Since wind velocity is a function of height h,
and Davenport's data was taken at a height of 33
scale,
scale.
to Davenport, the power spectral density function
is independent of height for
height
400
At a scale
feet
full
conversion factor is needed to transform the wind
tunnel spectrum to an equivalent full scale spectrum.
This
conversion is given by the following relation:
n
-
-m
=
-t33
n
m
= m)~
33J
where m is the reciprocal of the scale factor, and 4o is
velocity gradient power law constant.
-
39
-
the
4.
The Experiment
4.1 Introduction
Two types of tests were performed - a wind erosion test
to determine contours across the ground plane, and a hotwire
flow
test to measure certain statistical descriptors of the
electricaly.
An additional purpose of the wind erosion test
contours generated by
had on the position of the
direction
wind
and
height
building
that
effects
was to study the
the plastic granules which were blown away.
4.2 Wind Erosion Test Procedure
erosion
The quanities that could be varied in the wind
were
test
the building height, the wind direction, and the
gradient velocity.
During a typical run, the wind
velocity
would be varied, with the building height and wind direction
held constant.
The procedure is as follows:
First, the plastic granules are spread one layer
thick
over the ground plane in the region of interest (Figure 13).
Then,
the
distribute
ground
the
happens
after
the
first
one
about
increased to the next nominal speed.
speed
to
further
evenly
Then, the gradient velocity in
particles.
the tunnel is increased to
nothing
vibrated
is
plane
nominal
minute,
At the
speed.
the
first
speed
If
is
nominal
that some of the particles have been blown away, that
- 40
-
Then, a photo is taken
speed is maintained for two minutes.
After the photo
form a camera directly above the turntable.
is taken, the gradient velocity is
increased
or
either until all the particles have blown away
The
first.
occurs
gradient
After the required
decreased to zero.
next
The nominal speeds are increased
nominal speed (Figure 13).
whichever
the
to
60
si then
velocity
model
mph,
have
changes
been made, the process is repeated.
area
At the lower nominal velocities, a very small
the
ground
plane has had the particles blown away compared
These areas are locations where,
to the total area.
gradient
given
velocity,
the
wind
will
velocities
particles
still
remaining are small.
of
a
be
The areas have
In
very low velocities for a given gradient velocity.
type
for
At the highest nominal velocities, the areas that
greatest.
have
of
this
test, stagnation points show up as the points that
are the last to have the particles
blown
Care
away.
was
taken to record the stagnation points on film.
the
The runs that were conducted during
test
fall
particles
into
were
three
categories:
(1)
spread
relatively
thinly
wind
erosion
runs in which the
and
somewhat
unevenly, (2) run in which the particles were spread thicker
and relatively evenly, and (3) the final run
standard
procedure
was
modified
contours on the ground plane.
- 41
-
to
in
which
the
allow the tracing of
The first set of runs were conducted with the particles
spread
quite thinly over the ground plane - no particle was
lying on top of another particle,
typically
building
Five runs were tested in
height
directions
made,
the
particles
were
separated from one another by one or two particle
diameters.
degrees
and
in
tested
was
it
was
all
this
five runs was 1.0 feet.
were 0, 45, 22.5,
re-tested
0,
two times.).
decided
condition.
that
the
and
0
The
The wind
degrees
(0
After these runs were
particles
should
be
distributed in a thicker layer over the ground surface.
Using the thicker layer of particles, it was decided to
vary
the
building height, while keeping the wind direction
the same at 0 degrees. Six building heights were thus tested
-
1.0,
1.5, and 0.5 feet on one day, 0.25, 0.75, 1.25 feet
on the succeeding day.
wind
directions
After the six heights
were
tested,
of 45 degrees and 22.5 degrees were tested
with the building height equal to 1.0.
Since there was
a
delay
in
the
processing
of
the
photos, and it was necessary to proceed immediately with the
hotwire test because of scheduling constraints, a final
was
conducted
in
which
the
surface of the ground plane.
the
standard
procedure
contours
run
were traced on the
This required a departure from
used
in
the
previous tests.
On
previous tests, it was discovered that
the
drawing
of the contour would
instrument
in
the
- 42
vicinity
-
presence
of
a
change the location
traced.
of
Therefore,
the
contour
before
it
could
after the photograph for a contour was
taken, the gradient velocity was decreased to zero, and
contour
was
After
the
The velocity was then increased from
traced.
process
zero mph to the next nominal velocity, and the
repeated.
be
the
examining
was
data, it is
photographic
believed that this departure from the standard procedure has
caused some anomalies in the data.
In addition to the photograph
the next section.
minutes
after
This will be discussed in
taken
two
gradient velocity had stabilized to the
the
nominal velocity, a photograph was
taken
also
one
minute
after the velocity had stabilized to that nominal velocity.
4.3 Hotwire Test
The hotwire
test
designed
was
to
investigate
what
phenomonon,if any, was constant along the contours generated
The final
by the wind erosion test.
test
from
data
hotwire
consists of average, RMS (root-mean-square), peak, and
statisticaly predicted peak
discrete
points
on
measured peaks of
different
sampling
the
the
of
values
ground
same
plane.
phenomenon
rates are used.
velocity
the
filtering frequency.
from
It is known that
are
different
if
If the signal from the
hotwire is filtered, the measured peak will also
the
a
vary
with
It was decided that the filtering
frequency/sampling rate would be one of the parameters
would be varied in the hotwire test.
- 43
-
that
The total number of parameters
varied
in
this
that
could
have
been
test was five: (1) the x-y location of the
hotwire, (2) the filtering frequency/sampling rate, (3)
the
gradient velocity of the tunnel, (4) the wind direction, and
(5) the building height.
tunnel
time
to
investigate
decided to keep
the
constant
degrees
at
0
Since there was insufficient
wind
all these variables, it was
direction
and
1.0
and
feet,
building
when
the
hotwire
location coinciding with
velocity
was
set
contour
in
the
was
a
measuring
contour,
height
respectively.
addition, for most of the data gathered during
test,
wind
the
In
hotwire
the velocity at a
the
tunnel
gradient
equal to the velocity that generated the
wind
erosion
test.
Three
such
contours/velocities were tested: 30, 25, and 20 mph.
The procedure in each run of the
follows:
hotwire
test
relatively
high
changes,
velocity
the
wind
for
calibrated
as
described
later
tunnel
was
run
Then
in
the
a
this
hotwires were
section.
calibration yields five constants that are needed
as
This
input
data-taking computer program, HOTWI2: A0 and Al for
each hotwire, and the Baratron calibration constant.
the constants, etc.
to the flow.
After
are input, the program asks the user to
make sure the hotwires are mounted at gradient
exposed
at
about 1/2 hour to bring the
tunnel to temperature equilibrium.
the
as
Because the hotwire calibration is very sensitive
to temperature
to
is
height,
and
The program then re-calculates the Al
- 44
-
The
are
constants
A0
not re-calulated.
Before
at
hotwires
the
placing
the
in
pointed
the
that
direction of flow is noted, so
direction of flow.
Upon a signal from the
are calculated from a sample length of 16 seconds.
x-y
data
each
From
RMS, peak, and predicted peak velocity
average,
an
be
may
hotwires
the
14).
(Figure
locations, the
x-y
operator, the computer begins taking data.
point,
The hotwires are
plane
ground
then moved to locations on the
calibrating.
since
drift
constants to correct for thermal
For each
location tested, data points were taken for a number of
filtering
for
output
voltage
shown in Figure 15.
hotwire
Typical
rates.
frequencies/sampling
low and high filtering frequencies are
After all the data
points
taken
were
for a certain x-y location, the hotwires were placed back on
and the
their stands at gradient height
the
data
computer
This process was
that x-y location on disk.
for
recorded
repeated for each of the x-y locations tested.
The
8-second
extreme-value
the
16
predicted
peak
is- the
result
of
an
analysis conducted on 16 peaks extracted from
second
analysis
The
sample.
was
conducted
as
described in Reference [15].
To guard against errors in the data because of
drift,
the
Al
constants
were
re-calulated each time the
hotwires were placed at gradient height.
the
thermal
This insured
that
error in the data due to errors in the Al constants was
- 45
-
the
time
constants
were
limited to that occuring in a 15-minute period
needed
for
each
run.
the
However,
A0
-
It
re-calibrated.
recalulated only when the hotwires were
was decided to re-calibrate the hotwires if the Al constants
to
drifted more than 10
percent
from
calibrating
the
15
their
original
values.
The
for
procedure
conducted
as
follows.
Hotwire
average
recorded at several known tunnel velocities.
of
velocity
with
voltage
is
roughly
hotwires
was
voltages
were
The
variation
linear, and can be
described by the following relation:
Uwt = A
+ Al Vwt
where:
Uwt = general wind tunnel velocity
Vwt = general hotwire voltage
AS, Al = calibration
constants
After plotting the voltage vs.
wind velocity a staight
line was visually fitted through the points to obtain the AO
and Al constants.
Of all the data taken during the hotwire study, only
relatively small
ercentage of the data is usable.
was begun by sampling
locations
- 46 -
on
the
30
mph
a
The test
contour.
After
that
contour
was
almost completed, it was realized
that sampling at a constant
rate of 1024 Hz., while varying
the filtering
frequency
from 1 Hz.
inconsistent
data
the
accuracy
measuring
in
for
peaks.
extreme
filtering
freqency.
the data.
The
new
frequency
input
gain
it
in
sufficient
is necessary to
magnitude
greater
than
Hence, it was decided to re-take
proceedure
to
To
data,
sample at a rate about an order of
the
to 500 Hz., resulted
would
have
the
filtering
the computer program, which would then
set the sampling rate at ten times the filtering frequency.
Testing again commenced on the
30
mph
contour
line.
near the end of testing the contour line it was noticed that
the filter
type
"High-pass,
on
max
Investigation
oscilliscope
of
the
Krohn-Hite
flat",
the
instead
effects
revealed
that
of
filters
of
both
the
was
R-C
filters
set
network.
on
signal,
the
the High-pass, max flat filter
yielded peaks that were higher than unfiltered peaks of
same
to
the
while the RC filters yielded lower peaks than
the un-filtered signal.
It was thus decided that
the
data
taken up to that time was unsatisfactory.
Using the R-C network filters with the correct sampling
rates,
the 30, 25, and 20 mph contours were tested at their
respective
gradient
velocities.
Later,
various
x-y
locations not necessarily on contour lines were tested at 30
mph to aid in verifying the data taken earlier.
- 47
-
that
At one point during the testing, it was suspected
the gradient velocity varied across the width of the tunnel.
This would result in the two hotwires
different
being
calibrated
velocities at the beginning of each run.
to
To test
this variation, a special run was made in which the hotwires
were
exchanged.
The
difference
in
velocity at gradient
height between the two hotwires was measured to be
percent.
- 48
-
2
to
4
5. Analysis of Results
5.1 Introduction
phase
The main purpose of this
determine
of
the
test
was
to
a correlation between results of the erosion type
In the
of ground winds study and the hotwire type of study.
erosion test, additional data was taken to study the effects
that wind direction and the height of the
the
position
of
had
building
on
Theeresults of the erosion
the contours.
test will be discussed first, followed by the
test
hotwire
and the correlation between the two tests.
5.2 The Wind Erosion Test
The data from the wind erosion test
falls
into
three
categories: (1) data obtained when the particles were spread
the
thinly, (2) data obtained when
more
thickly
particles
were
spread
and uniformly, and (3) the final run when the
,velocity was decreased to zero between each contour.
Data obtained when the particles were spread thinly has
certain advantages and disadvantages.
smaller
the particles can respond to
gusts.
or
higher-frequency
Another advantage is related to the fact that there
are less total particles on
contours
One advantage is that
the
ground
plane.
When
the
are being formed, the particles tend to form piles
along the contours where the direction of flow is
- 49
-
into
the
of particles.
field
When a pile of particles forms that is
to
two or more particles deep, they are less sensitive
the
In most of the data taken this way, there is quite an
wind.
amount of detail in the shape of the contours, especially on
the
leeward
these patterns is that they may
vortices
One possible reason for
side of the building.
have
formed
the
by
being shed off of the corners of the building, and
these vortices tend to be stonger at
areas more than others.
some
been
the
ground
plane
in
If this is true, then using a
thin layer yields useful information about the character
of
the flow in various areas of the ground plane.
Another possible reason
for
the
formation
of
these
patterns is that they are caused by uneveness in the initial
distribution of the particles.
That is, where the particles
are more thinly distributed in the first place, they will be
more likely to be blown away, or be blown into an area where
is
there
already a thicker layer of particles that is more
resistant to being blown away.
The author believes that both phenomena have an
impact
on the shape of the contour, and that the relative impact of
each varies with position across the ground plane.
At
the
higher gradient velocities, some of the data taken at a wind
direction of zero degrees seems to indicate that some of the
at least is due to detailed structure of the
small
detail,
flow.
A good example of this is the small area of
- 50 -
scouring
close
to
the
leeward
x=0.75 feet, y=0.
from
the
two
side
of
the building, centered at
feet (Figure 16).
The fact that the data
repeat runs taken at this wind direction are
similar indicates that it was not caused by random uneveness
in the initial distribution of the particles.
It is evident, however, that the detail in the contours
at
other
points
is
definitely caused by uneveness in the
initial distribution of the particles (see Figure
was
decided
after
runs
five
that
out-weighed the advantages, and that
the
the
20).
It
disadvantages
particles
should
not be distributed so sparsely.
The initial distribution
chosen
of
the
particles
was
then
to be such that no particle would be lying on top of
the other, but that they also would be touching
other
each
approaching a close-packed situation.
This resulted in more
uniform data
being
than
the
with the contour
previous
more from
the
direction
of
runs.
particles
flow
lines
much
smoother
However, the data suffered much
piling
up
in
heaps
where
the
It is
was into the field of particles.
obvious that the contour at this point was not measuring the
same quantity as at a point where no piling was occuring.
Examining the data from the first six runs taken
wind
a
direction of 0 degrees (Figures 21 to 26), we see that
the location near the windward corners of the
the
at
locations
with
the
highest
- 51
-
building
wind velocities.
are
As the
gradient velocity is increased,
expand
outwards.
At
these
two
scour
patterns
some intermediate gradient velocity,
the patterns merge in front of
the
windward
of
face
the
As the gradient velocity is increased to about 35
building.
mph, most of the particles have blown away, and the presence
of
particles
indicate
relatively
calm
velocity is increased still further, the
calmest
the
areas
of
All of the data
all - the stagnation points - are revealed.
indicated at least two stagnation points, one
the
As
areas.
in
of
front
building at a distance from the front face ranging from
.38 to .65
building,
feet,
and
one
on
the
side
leeward
the
of
typically located about .25 feet from the leeward
face.
The data taken with the building height equal to 0.75
seems
to
indicate
more unstable stagnation point
another
located about 0.75 feet downstream of the
leeward
face
of
the building.
The location of the up-stream
function
appears
of
that
asymtocicaly
building
the
stagnation
point
as
of
the
points
stagnation
approaches a value of about 0.65 feet from the
front face of the building as the building height gets
large.
It
height is depicted in Figure 27.
distance
a
Although
this
value
very
would vary as the plan shape
and/or wind direction or boundary layer profile
is
varied,
the same general trend would apply.
The area of particle scoured
- 52
-
away
as
a
function
of
gradient velocity for various building heights is plotted in
Figure 28.
The area with particles scoured away as a
building
height
in Figure 29.
are
of
for various gradient velocities is plotted
The contours that this plot is
presented
in
Figures
30
to 34.
lowest gradient velocity, 20 mph, an
height
function
derived
from
Notice that for the
increase
in
building
past 0.75 feet appears to have no effect on the size
of the contour.
velocities
The
indicate
contours
that,
from
as
the
the
higher
building
gradient
height
is
increased, the area affected by the building increases.
increases
quickly
slowly, just like
building
at
the
discussed
first,
and
stagnation
earlier.
then
points
This
data
It
it increases more
forward
of
the
indicates
that
although larger buildings generally increase the velocity at
the ground plane, a more significant effect is that the area
that these high velocities occur over is also increased.
The data from the wind erosion test indicates that
case
of
a block building with the wind direction set at 45
degrees is the
velocities
more
near
extreme
case
the ground plane.
with
respect
0,22.5,
and
45
to
directions
degrees is depicted in Figure 35.
contours for wind directions of
22.5
and
shown in Figures 36 and 37, respectively.
- 53
-
high
The difference in scour
area as a function of gradient velocity for wind
of
the
45
degrees
The
are
For data
degrees,
with
the
wind
building.
velocity
was
They
expanded
increased.
direction set to 45 degrees, the
form
direction
outward
to
0
expanded in size and reached the
evident
in
as
the
However, with the wind
contour
was
away from the corner of the building.
Also
set
the contours were observed to begin forming at the
corners of the
gradient
taken
corner
observed
to
It then quickly
of
the
building.
the 45 degree data was an isolated stable
scour area located directly downstream of the leeward corner
of
the
building.
A
similar pattern was generated in the
22.5 degree data, although its area was not as
zero
degree
data exhibited no such pattern.
taken at zero degrees using a very
same
large.
pattern
thin
The
However, data
layer
showed
the
in the flow, indicating that at zero degrees,
the vortex in this area is present, but it was
much
weaker
than it was at 45 degrees.
The area of scour of the thinly
averages
distributed
about 30 percent higher than the area of scour for
the more closely distributed particles.
occur
because
respond to
particles
the
lower
more
thinly
velocity
gusts
This is believed to
distributed particles can
than
the
more
closely
distributed particles.
Investigation of the wind erosion
the
last
run
reveals
data
obtained
from
contours that contain significantly
smaller area than the contours obtained from
-
54
-
previous
runs
(Figure
38).
It appears that the difference in the data is
caused by the difference in the procedure
types
of
runs.
between
the
two
The data indicates that if the velocity is
brought to zero between each contour, more time is needed at
the
nominal velocity in order to obtain the same results as
when
the
Beranek
velocity
and
Van
on
not
Koten
their investigation
collected
is
decreased
between
contours.
5] noticed the same phenomenon in
using
particles
of
sand.
The
data
the final contour indicates that the time the
tunnel is run at the nominal velocity before taking data
a
consideration
even
is
for relatively large particle sizes.
This is a further indication that it is the peak gusts
that
are causing the particles to move.
It is also evident from the data from the erosion
that
the
flow
in
the tunnel test section is not constant
across the test section.
faster
Specifically, the flow seems to be
in a region about 0.5 to 1.0 feet from the left side
of the building ( .6 < y < 1.2).
confirmed
The wind erosion
data
is
in this regard by the hotwire data that was taken
in this region.
been
test
In hindsight, wind erosion data should have
taken with the building not in place, to determine any
assymetries
possible,
in
the
flow
in
the
test
section,
and
if
to correct them before the testing commenced.
In
any subsequent tests, it is recommended that this be done.
- 55
-
5.3 The Hotwire test
The main purpose of the
information
at
various
hotwire
locations
test
on
was
to
gather
the ground plane to
determine whether any wind velocity (average, rms, peak,
combination)
is
constant.
on the 30, 25, and 20
erosion
test
were
For this reason, test locations
mph
contours
chosen.
the 30 mph contour,
seven
or
from
the
final
wind
Eight locations were chosen on
locations
were
chosen
on
the
25-mph contour, and five locations were tested on the 20-mph
contour.
kinds
Test locations were
of
flow
around
conditions on the
locations
the
chosen
contour
building
as
varied
behind
different
so
as
to
make the
as
possible.
Some
of
flow.
Others
were
the leeward face of the building, where the
flow is separated and very
located
sample
were located in front of the windward side of the
building where there is a reversal
located
to
turbulent.
Still
others
were
on the contour directly in the wake of the vortices
originating from the windward corners of the building, where
the
average
velocity
relatively high.
is
high
The remainder
and
of
the
points
turbulence
were
taken
is
at
locations on the contours where the average was high and not
positioned in the wake of the vortices.
the
experiment
was
designed
so
quantities were discovered, it
character
of
the
flow
Additional data was taken
at
at
- 56
One
that
would
not
can
if
be
any
see
that
constant
because
the
all points tested was similar.
points
-
not
on
the
contour
locations to verify the data taken at the contour locations.
The locations where data was taken is shown in Figure 39.
Data
peak,
consisted
of
average,
root-mean-square
and eight-second estimated peaks.
at several filtering frequencies.
on
all
Hertz.
the
contours
The
(RMS),
All data was taken
frequencies
sampled
were 1,2,4,6,10,15,20,40,60, and 100
At a few selected points, data was also taken at 200
Hertz.
In Figure 40, the average data
corresponding
were drawn.
of
the
are
plotted
at
their
x-y locations, and constant velocity contours
The average velocity is highest near the
sides
building at about 0.5 feet from the building sides.
To the leeward side of the building, the average velocity is
relativly
low, indicating the region of separated flow that
is expected.
In front of the windward side of the
is
of relativley low average velocities, agreeing
with
an
area
the
wind
erosion
data.
This
also
building
indicates
the
presence of a stagnation point.
The direction of flow was sampled at various
over
locations
the ground plane with the metal rod with the thread on
the end described in section 2.
This data
is
depicted
in
Figure 41.
Root-mean-square and peak data are depicted in the same
way
as
the average data in Figure 42 and 43.
- 57
-
Both the RMS
and peak data were taken at a filtering frequency of 60
The
high
turbulence
regions
in the two wakes originating
from the forward corners are clearly evident.
are
the
regions
on
either side, where
higher
the
the
Also of
RMS
and
peaks
are
significantly
The fact that the shapes of
the contours in Figures 39 and 43 are similar is
that
it
is
note
windward face of the building to
than would be expected.
indication
Hz.
the
peak
a
further
gust that is moving the
particles.
Various investigators have attempted to find a velocity
parameter for pedestrian comfort [5.
One way is to use the
peak velocity that was measured in a sample
duration.
Another
way
that
given
time
is to calculate a quantity that is
dependent on the values of the
such
of
average
and
RMS
velocity,
y = avg + (k)(RMS), where k is a constant.
Both
methods will be discussed in this section.
Data was taken for various filter
at
all
cut-off
frequencies
of the locations on the ground plane because of the
hypothesis that the phenomonon that was constant
contour
along
the
line was a gust of certain duration and strengh, or
some combination therof.
hypothesis
was
to
take
The method
vs.
the
to
test
this
data at the same x-y location and
vary the filtering frequency.
coefficients
chosen
Plotting
filtering
filtering frequency axis a log
- 58 -
scale,
the
peak
frequency,
indicates
velocity
with
a
the
linear
variation
of
frequency).
estimated
peak
coefficients with log(filter
Within the randomness of the extreme value type
data, this linear variation was displayed in the data at all
of
the
x-y
locations,
considerably
from
location
typical locations are
estimated
peaks
although
shown
were
used
the
slopes
to
location.
in
Figures
instead
could
Plots
44
to
vary
of some
47.
The
of the measured peaks
because the random variation of the estimated peaks has been
shown
to
peaks
[16].
be
significantly
The slopes
estimated
of
peaks
the
less than that of the measured
linear
(herafter
relationship
simply
with
the 1 Hz.
since this quantity
velocity.
If
at
The intercept of each
line also varies from point to point,
is
mainly
dependent
on
all the lines for a contour
other at a certain frequency, then
frequency
which
the
called "peaks") and log
frequency varies from point to point.
line
between
that
the
average
intersected
frequency
each
is
the
the peak velocities are constant along
the contour.
Unfortunately, because the
often
slopes
of
the
are
nearly equal, and because of the experimental scatter
in the data, it is difficult to determine at what
the
lines
data
calculate
contour.
matches
coefficient
The
best.
of
Another
approach
frequency
would
be
to
variation for the points on a given
frequencies
at
- 59
which
-
the
coefficient
of
variation is
a
the
indicates
minimum
general
of
range
The
frequencies at which the peaks are relatively constant.
plotted
coefficient of variation for each contour is
of
function
frequency
indicate a minimum at 60 Hz.
taken
was
Since data for a whole contour
only one frequency higher than 60 Hertz (100
at
Hz.), the reliabilty of the upward trend in
high as one would like.
One aim of any further tests should
how the coefficient of variation varies
investigate
to
along the contour at frequencies higher than 100
such
a
of
coefficient
with increasing frequency past 60 Hertz is not as
variation
be
a
The data seems to
48.
Figure
in
as
With
hz.
test, it could be determined whether a minimum does
indeed occur,
decrease
if
or
with
Hz.
or 100 Hz.
the
data
will
random
the
variation
of
is used, the coefficient
on
to
Whether a filter frequency of 60
frequency.
be
continues
variation
in
the order of about 0.1, if no other
correction is made to the data.
Another method of describing gusting flow is to
a
to
equal
velocity
constant with the RMS.
the
average
In figures 49
define
the product of a
plus
the
54,
to
average
plus multiples of the RMS are plotted for the points on each
contour.
was
that
values of
showing
The average and RMS that was used for these
of
the
rough
100
Hertz.
peaks
for
agreement
describing the flow.
plots
Superimposed on these plots are
various
between
the
In this experiment
- 60
-
frequencies,
filtering
two
one
methods
of
was
to
goal
determine which method yields more constant results over the
contours.
When comparing the two methods, one needs to
the
appropriate
value
of
k
to
determine
The value of k was
use.
determined for each contour using the following relation:
(1)
k = (peak-avg)/rms
on
For each point
contour,
the
a
of
value
k
From these calculated values, an average value
calculated.
equation
of k was determined, and subsituted back into
initial calculation of k, a question arises as to which
be
used
RMS
in the calculation, the total (unfiltered)
RMS, or the filtered RMS at some frequency.
In
Figure
55,
filtering frequency used for
value of k is plotted vs.
the
(1)
In the
to yield a value that can be compared with the peak.
should
was
the peaks, for various values of the filtering frequency for
which
the RMS was measured.
One can see that the variation
of k with filtering frequency of the peaks is
about
RMS.
6
to
10
linear
Hertz for all filtering frequencies of the
Also of note is the fact that the data for
filtering
frequency
frequency
of
the
frequencies.
above
RMS
Thus,
the
of
peaks
line)
(dashed
this
is
is
the
linear
the
filtering
for
all
the only way to consistently
treat the data.
- 61
equals
which
-
Since k was found to vary slightly
height
in
the
tunnel,
it
was
with
decided
the
gradient
to treat all the
contours separately in the calculations discussed next.
The
coefficients
calculated
using
of
variation
equation
(1)
of
was
out
for
the
coefficients
depicted in Figure 56.
obtained
using
This
using the
calculation
was
the same filtering frequencies as for the
calculation involving
resulting
velocities
determined
average value of k for each contour.
carried
the
the
peaks
of
discussed
variation
The
for each contour are
The general shape is similar to that
predicted
always much higher than
earlier.
those
peaks,
but
obtained
the values are
using
the
peaks.
These calculations indicate that on a contour, the peaks are
more constant than the velocities obtained by using equation
(1) where
k is a constant.
Similar calculations were performed using the square of
the
velocities
themselves.
or
(pressure),
instead
of
the
velocities
This calculation was performed to test
whether
not the peak dynamic pressure is more constant along the
contour than
performed
results
the
using
peak
both
indicate
velocities,
not
that
velocity.
methods
the
The
calculations
discussed
contours
are
were
previously.
The
dependent
on
velocities squared, since the coefficients
of variation of the
pressures
are
velocities.
- 62
-
much
higher
than
the
The k factor was
velocities
for
calculated
different
The
about
The data is
10
non-linear
Hertz,
and
plotted
(Figure
for
of
the
in
Figure
frequencies
approximately
frequencies greater than 10 Hertz.
velocites
square
k factor for which the RMS and peak filter cutoff
frequencies are equal is
than
the
combinations of the RMS and peak
filter cufoff frequencies.
57.
for
The
k
less
constant
factor
for
for
the
55) is linear for all frequencies in-the
range of frequencies tested.
When the data was being
taken
for
the
wind
erosion
test, it was noticed that the particles tended to form piles
at some locations on the contours, and
other
locations.
Most
of
the
not
form
situations
piles
where
occured were when the direction of flow was into
of
particles, and away from the scoured area.
of the gust needed to blow
greater
than
if
the
away
trying
particles
to
into
the
field
The strength
particles
is
the
particle
particle,
and
accuracy
of
the
gust
is
blowing
scour area away from the field of
resistance
of
the
the gust needed to move the particle
should be of lesser strength.
the
blow
If the
particles, there is just the frictional
single
of
the
into the field of particles, the adjacent particles
will tend to resist any movement.
the
pile
piling
particles were just one layer thick.
Because the gust of wind is
further
a
at
One possible way
to
improve
wind erosion test in predicting peak
gusts would be to introduce a correction factor
- 63
-
to
account
for piling of the particles.
Two types of correction factors
account
for
were
investigated
the effect of the particles piling up.
method, the angle between the contour and the
flow was recorded.
to
In one
direction
of
In the other method, the locations along
the contours where the particles formed piles, and how thick
these
piles
were,
was recorded.
disadvantages to both methods.
There are advantages and
Measuring
the
approximate
angle between the contour and direction of flow is easy, but
takes additional time during the test.
takes
almost
no
additional
time
involves more judgement on the
The
typical
ground
wind
at
during
part
of
the
the
method
test,
but
investigator.
recording
the
direction
of
the ground, so only the latter method can be used.
Both methods were evaluated
predicted
second
studies being considered in this
report were conducted without
flow
The
peak
with
respect
to
accuracy
of
gusts for the tests conducted on the simple
building shape.
For each x-y location on the three contours tested, the
direction
of
flow
was
recorded.
compute the angle between the
contour.
tested.
58.
zero.
This
direction
data was used to
of
flow
and
the
These angles are given in table 5.1 for the points
The angles in Table 5.1 are as
defined
in
Figure
When the flow is into the scour area, the angle equals
When the angle is directly away from the scour
- 64
-
area,
angle
equals 180 degrees.
When the flow is parallel to the
contour line, the angle equals 90 degrees.
each
contour
have
been
The
peaks
for
plotted as a function of angle in
Figure 59 for various filtering frequencies.
The data seems
to indicate that the peaks are roughly related to the cosine
of the angle.
The correction factor that was chosen is
(cos(e) - 1.0) .
This correction factor has the effect of
reducing all the peaks to the value they might have
there
was
no
k2=
had
if
piling up of the particles along the contour
line.
To assess the effect of this correction, the amount
the
of
correction to the data was varied when calculating the
coefficient of variation for
the
peaks
on
each
contour.
Since the peaks taken at 60 Hertz had the lowest uncorrected
variation,
the
calculation.
60
This
Hertz
data
peaks
for
were
each
chosen
for
contour is depicted in
Figure 60.
The optimum value of kangle ranges between
and
The
3.0.
improvement
ranged from zero
improvement
of
to
about
about
in
45
16
this
zero
accuracy using this method
percent,
percent
with
an
average
using a value of kangle
equal to 1.5.
The other method of correcting for the piles formed
the
particles
was simply to record how much piling occured
at the various locations on the contour.
technique
to
by
For this
kind
of
be useful in a ground winds study, it must be
-
65 -
relatively convienient to use.
of
piling
of
the
For this reason
particles
was
divided
the
degree
into
three
categories:
(0)
no piling of particles
(1)
some piling of particles
(2)
large amount of piling of particles
These categories were relatively easy to apply
erosion
wind
test
data.
to
the
When the particles are in their
initial condition with no wind blowing in
the
tunnel,
the
x-y grid on the ground plane is visible through the layer of
When the particles started to form more than one
particles.
the
layer,
grid on the ground plane was no longer visible.
This criterion was used to
and
(0)
(1).
distinguish
From the photographs it is also possible to
determine areas where the particles have piled
thick
layers,
although
up
in
very
the distinction between categories
(1) and (2) was not as clear as between (0) and
tested
categories
between
location as identified in
(1).
Each
Figure 39 was assigned to
one of the three categories as shown in Table 5.2.
Table 5.2 - Degree of Piling for Ground Wind Locations
(0)
1,2,3,11,12,21,22,23,31,32,33,41,42,51,52
(1)
4,10,13,16,17,34,35,36,37,43,44,45,53,54,55
(2)
5,6,7,8,14,15,24,25,26,27
- 66
-
To evaluate this method, corrected peaks were
computed
by the following formula:
new peak = old peak
+ (-l.)*(kpile)*(category number)
The coefficients of variation for
function
of
kpile
each
in
as
a
The range of
The improvement
accuracy of the peaks along the contour ranges from
the
zero to 56 percent.
1.5
contour
is depicted in Figure 61.
optimum values of kpile is from zero to 3.0.
(2)
yields
an
of
The average optimum value
average
improvement
of
kpile
=
20 percent
about
compared to the uncorrected data.
We can see that the method involving direct measurement
of
the
degree
of piling of the particles, crude as it is,
yields as much improvement in
the
accuracy
of
the
peaks
along the contour as the method involving the measurement of
the angle between the contour and the direction of flow.
Further examination of the corrected data to
whether
there
are
any
other
trends
determine
that can be used to
further reduce the scatter in the data reveals that the
locations
closest
to
corrected peak values.
occur
on
building.
building
the
the
building
typically
The points closest to
windward,
side,
and
leeward
x-y
have lower
the
building
faces of the
Apparently, the points on the leeward side of the
measure
corrected peaks,even though the particles
- 67
-
have formed large piles.
application
of
another
This
trend
correction
indicates
factor
that
will
the
yield
a
further improvement in the accuracy of the data.
When deciding
factor,
on
how
to
define
a
such
correction
methods of construction can be considered.
several
First, it has to be decided if the distance to
measured
be
is to be the distance from any point of the building, or the
distance to the nearest corner, since the
gusts
tend
to
from
determine
what
function
of
the building best describes the reduction in
peak gust as the testing location is
building.
causing
originate from the corners of the building.
The other consideration is to
distance
vortices
Since
moved
closer
to
the number of points tested is relatively
small, and the number of points affected by this
factor
even smaller, it was decided to use a step function.
point was
closer
building,
the
the
than
0.25
feet
to
any
point
If the
on
correction was applied to the point.
location was further than 0.25 feet from any
point
is
the
If the
on
the
building, the correction was not applied to the point.
The coefficients of variation for the peaks using
this
correction were calculated using the following expression:
new peak = old peak - (kpile)*(category)
- (kdist)*(dist cat)
- 68
-
(3)
The points affected
7,8,27,28,37,38,
by
41,45,51,
this
and
correction
55.
The
were
points
coefficient
variation of the contours is plotted as a function of
for
kpile
=
1.5 in Figure 62.
in
to
not
3.0
yielding
the scatter of the data ranging from zero to
43 percent compared to the data using the
but
kdist
The optimum value of kdist
for the various contours ranges form zero
reductions
of
both
corrections.
For
first
correction
kdist = 1.5, the average
reduction of the scatter in the data is about 10 percent.
In
all
of
the
analysis
discussed
contours were-analized separately.
previously,
the
It was not neccessary to
consider the effects of the wind tunnel gradient velocity on
the
estimation of the peaks along the contour.
of the peaks as a
tunnel
is
function
of
gradient
plotted in Figure 63.
63 indicates the kind of variation
The average
velocity
in
the
The dashed line in Figure
with
gradient
velocity
that can be expected if the peak velocity along the contours
is a constant.
The coefficient of variation of the data as a whole was
calculated
using the correction
for the uncorrected data.
reduced
from
.225
gradient velocity.
to
for
gradient velocity and
The value of the coefficient
.200
by
using
It is evident that
was
the correction for
the
correction
for
contour gradient velocity is significant, although it is not
as effective as the correction for piling of the particles.
- 69
-
Of the other correction factors to the peak data, kpile
the
offer
to
seems
However,
accuracy,
the
all
since
kangle
and
kdist.
factors
are
relatively convenient to use, they
followed by
correction
in
improvement
greatest
all should be used whenever possible.
In order to compare the data obtained from this test to
tests
other
which
may
have
had
the
data filtered at a
different frequency, a method needs to be used to
calculate
the effects that a different filtering frequency may have on
the data.
One convenient way to compare
calculate
the
to
is
data
average values of the gust factor k obtained
Figure 64 depicts the average value
from both tests.
of
k
from the data as a function of filtering frequency
obtained
for
such
values
different
of
gradient
the
This
velocity.
relationship can be expressed by the following equation:
k = ( 2.2 + (0.08 * log (")))
(4)
* (1. + 0.016 *(Vgrad - 2))
It
obtained
must
in
remembered
be
that
all
the
hotwire
this test was obtained from just one condtion:
building height = 1.0, wind direction = 0 degrees.
note
is
the
data
fact
Also
of
that the situation tested was that of a
tall, massive building form located in the middle of an open
field.
It
is
thus
necessary to verify the relationships
discovered as a result of testing this model with test
-
70
-
data
gathered
from
conditions.
models
with
much
more
realistic boundary
In the next section, data from a model
of
the
University of Minnesota will be compared with the results of
the test using the model of a simple building shape.
- 71
-
6.
Correlation with Other Tests
a
test
previous
In the
simple
shape
building
Some relationships were found between the contours
tested.
of the erosion test and the peak velocities measured in
hotwire
was
It
test.
desirable, however, to verify these
is
relationships in situations that are not as
building
usually
are
Buildings
tested.
the
environments, therefore an attempt was made
as
simple
the
tested in urban
verify
to
the
results of the previous test using data collected from tests
of buildings in their urban setting.
the
Such a test has been conducted for
Minnesota
for
campus
the
for
Center
in
Both erosion and hotwire tests were
Minneapolis, Minnesota.
conducted
of
Sciences
Health
proposed
the
University
existing building in
the
with
place, and for the proposed building in place.
80
A
total
of
ground wind stations were tested in the hotwire studies,
40 in each building configuration.
However, since
some
of
the points were not visible from the camera mounted directly
61
overhead, only
the
of
were
points
80
used
in
the
for
the
correlation study.
The
velocity
gradient
parameters
measured
boundary layer used in the University of Minnesota test were
@=.31, hg= 37.5 inches.
1:400.
For
a
more
The scale of
the
model
used
was
detailed description of the simulated
flow, the reader is refered to
- 72
the
-
report
describing
the
ground wind study conducted
17.
The procedure for correlating the results
tests
first
test
that
contours
of
the
two
involved tracing the contours from the erosion
were
are
recorded
reproduced
on
photographic
film.
in Figures 65 to 80.
These
The nominal
gradient velocities for the erosion study were 20,30,40, and
either
50
or
60 mph.
Some of the higher contour gradient
velocities are equal to 60 mph because of an
test
procedure.
error
in
the
About 25 percent of the data uses 60 mph,
the remainder uses 50 mph.
The next step in the procedure was to use
the
contour
data to estimate contour gradient velocities for each ground
wind station for each direction.
hotwire
station
occured
When
the
location
velocities.
a
between two contours, the contour
gradient velocity was interpolated between the
gradient
of
two
contour
If the location of a hotwire station
was such that the particles were never blown away for a wind
direction
for the gradient velocities tested, the point for
that wind direction was not used in the analysis.
the
particles
were
Also,
if
not initially distributed at a hotwire
location for a certain wind
direction,
the
data
was
not
available, and hence not used.
In the hotwire test, the statistically
were
not
recorded
measured
peaks
for about 25 percent of the data taken.
In the correlation analysis,
-
both
73
-
measured
and
estimated
peaks were analyzed.
The
hotwire
gradient
data
velocity
contours, and
section 5.
k
was
required
factors
then
for
were
sorted
a
by
fixed
computed
the
contour
velocity on all
as
described
in
The k factor is given by the following relation:
k = (peak - average)/ rms
These k factors for the measured peaks as a function of
the
estimated
Figure
81.
relationship
contour
The
k
gradient velocities are depicted in
factor
follow
a
roughly
with respect to the estimated contour gradient
velocities, with a large amount of scatter.
for
linear
The
k
factors
the test of the simple building shape are also plotted.
There is relatively good agreement in the slopes of the
sets
of
data.
The reason why the University of Minnesota
data falls below the prediction from the test of the
building
shape
two
simple
may be that the particles in the University
of Minnesota test were distributed very thickly, thus moving
the
plotted
line
to
the
right
in Figure 81.
particles in the University of Minnesota
than
those used in the test
of the
test
simple
Also, the
were
larger
building shape
(2 x 2 x 3 mm. vs. 1.5 x 2 x 2 mm.).
Using the contour gradient velocities from
to
80,
the
Figures
65
actual estimated peak velocity at each hotwire
station for each wind direction was calculated.
was then sorted by contour gradient velocity.
- 74
-
This
data
The peaks vs.
contour gradient velocity are plotted in
with
the
uniformly
The
than
15
Velocities with greater than 15 points are
The
have
that
less
plotted with a triangle in Figure 82.
are
points
square.
is
data
distributed with respect to contour gradient
The contour gradient velocities
velocity.
along
of variation calculated for the data
coefficient
collected for each contour gradient velocity.
not
82,
Figure
dotted
through
line
with
plotted
the
data
shows
an
velocity
gradient
approximate relation between the contour
a
and the expected value of the peak that would be measured at
For the data for which more
that contour gradient velocity.
than
15 points were collected, the coefficient of variation
tends to be equal to approximately 0.19.
This relationship of the contour gradient velocity with
the
value
expected
normalized values of
station.
The
peak
by
the
multiplied
and
location
of
the
measured
peaks
at
to
generate
ground
each
gradient
contour
velocity
for
that
wind direction, and then divided by the value
calulation
that
contour
gradient
velocity.
was performed for each ground wind station
over each wind direction.
average
used
was
coefficient from the original data was
of the peak expected for
This
peak
the
For each ground wind station, the
of the normalized peaks for all wind directions was
calculated,
along
variation.
This
with
data
the
associated
coefficient
is depicted in Figure 83.
great scatter evident in the data.
-
75 -
of
There is
Upon careful observation of the data in Figure 83,
notices
that
the
ground
wind stations with significantly
lower normalized average peaks are those locations that
very
close
one
to buildings.
are
Also note that those points with
low coefficients of variation are those that are
not
close
to any building boundaries.
Another calulation was performed taking
the
proximity
of a ground wind station location to buildings into account.
This correction improves the scatter in the
of
the
peak
expected
value
over the total number of points, but does not
improve the scatter of the data that is
caused
within
the
data
at each point by the variation of the normalized peaks
with
respect
to
wind
direction.
The
coefficients
of
variation are on the order of 0.2.
A similar procedure was conducted for the statistically
estimated
depicted
peaks.
in Figures
The
results
84 to 86.
of
these
calculations is
Of note is the
fact that
the
scatter in the data is not reduced by the "improved" method.
This may be due to the fact that the sample size is somewhat
smaller.
A
more probable explanation is that the error in
the data is not due to errors in the
the
peaks
in
the
hotwire
velocities at the tops of the
in
sampling
test, but by the fact that the
particles
than that measured by the hotwire.
- 76
accuracy
-
may
be
different
Since the
thick
particles
layers,
the
the same phenomenon
model.
Also,
were
distributed
in
relatively
field of particles may not be measuring
that
since
was
the
measured
particles
using
were
the
very
distributed, it is almost impossible to apply
a
simple
thickly
correction
for piling up of the particles.
Since the angle of flow for the hotwire
recorded,
a
correction
flow and the contour
was
not
for angle between the direction of
is not possible.
The absence of these two corrections
cause
test
is
part
of
the
for the significanly higher coefficients of variation
measured in
the
University
of
Minnesota
test.
Another
obvious difference between the two tests is that the contour
gradient velocities in the test of
the
simple
shape
were
relatively well defined, while the contour velocities in the
University
of
Minnesota
test
were
interpolated
between
widely-spaced contours.
It is evident that with the data from the University of
Minnesota
test,
it
the peak velocities
is not possible to obtain estimates of
from
the
contour
velocities
coefficient of variation much less than 0.2.
stations
buildings
are
the
tested
that
are
reliability
of
improved.
-
77
-
not
the
a
If ground wind
relatively
method
with
is
close
to
somewhat
A similar analysis was performed
using
data
obtained
from a ground wind study for the City of Buffalo, NY.
locations were chosen from the 37
wind
erosion
data
and
The contours drawn from
available.
are
photographic
locations
in
reproduced
Figures 85 to 102.
tested.
hotwire
the
Eight
Both
data
were
photographic
data
The model scale was
1:600, with values of hg = 43.5 inches, and o = .284.
Both
the hotwire and erosion data were available for sixteen wind
directions, compared to eight directions for the
University
of Minnesota wind erosion test.
From the contour
obtained
as
for
gradient
drawings,
the
velocities
University of Minnesota data.
were
These
contour gradient velocities are tabulated in Table 6.2.
analysis
was
then
performed
similar to that done for the
University of Minnesota data to obtain k
velocites
the
vary
University
much
of
Minnesota
and
104).
An
normalized values of
location
over
all
analysis
the
wind
coefficients of variation.
the
gradient
velocity
somewhat
peak
coefficients
data
the
peak
over
lower
(Figures
was then performed to obtain
of
the
peaks
directions,
and
the
average
at
each
associated
It was found that correcting for
in
the
tunnel
improvement in the scatter of the data.
peak
and
less with the gradient velocity, and
the coefficients of variation are
103
factors
as a function of gradient velocity in the tunnel.
Compared to
velocities
An
yielded
little
The average of
the
all wind directions is plotted for
- 78
-
each location in Figure 105, with no correction for gradient
speed in the tunnel.
A similar analysis was conducted for the
estimated
peaks.
The
statistically
results are shown in Figures 104 to
106.
One important
Minnesota
difference
between
the
University
of
test and the test for the City of Buffalo test is
related to the type of hotwire probes
that
were
each
City
of Buffalo were
test.
The
hotwires
for
the
used
positioned such that the center of the wire was at a
of
0.15 inches.
height
The center of the wires for the University
of Minnesota test were positioned at 0.30 inches - a
of
two
greater.
the
A
probable
the height of the particles.
to
Some
investigate
closer
to
The fact that the hotwires are
not measuring the flow at the height
data.
cause
improved coefficients of variation for the Buffalo
test is that the hotwires are measuring the flow
believed
factor
The height of a typical particle used for
both tests is about 0.05 - 0.07 inches.
for
for
of
the
particles
is
be the significant cause of the scatter in the
recommendations
this
factor
will
section.
-
79
-
for
further
be
discussed
testing
in
to
the next
7.
Conclusions
It is evident from
sections
that
an
the
discussions
in
previous
the
approximate relationship can be descibed
between the peak gusts measured in a hotwire study, and
contours generated by the erosion type of study.
evident
that
the
correlation
between
the
the
It is also
data
has
a
coefficient of variation that is too large to be of use in a
commercial ground
wind
The
study.
high
of
coefficient
variation has its cause from four types of errors:
1) errors in the erosion test procedure
2) error in measuring the data with hotwires
3) errors in the correlation procedure.
4) The erosion particles and the hotwires are
sensitive to velocities at different heights.
The errors in the procedure are several.
One error
is
related to the fact that the velocity in the tunnel is quite
for
difficult to set accurately and quickly - a requirement
the
erosion
type
of study.
Some instrumentation to allow
the investigator to set the tunnel speed more
easily
would
improve the 'repeatability of the method.
The method of distributing the particles also needs
to
be improved so that the initial distribution of particles is
more even.
It would also be helpful if the problem
particles forming piles could somehow be avoided.
- 80 -
of
the
The wind erosion technique may also benefit from
different
sizes
and
using
shapes of particles, and changing the
roughness of the ground board.
Error of the second type is
encountered
when
using
related
hotwires
to
two
problems
to measure the flow: (1)
errors due to temperature drift, (2) errors due to
direction of the flow (Figure 9).
changing
Irwin [18] has documented
a pressure instrument to measure pedestrian level winds that
he has used successfully in his laboratory that is direction
independent and has much less problems with drifting of
calibration
because
of
temperature
Use of this instrument should be
the
changes (Figure 109).
investigated
with
future
ground wind studies in mind.
Errors of the third type occured partially because
contours
plane
were
and
so
widely
interpolation
the
spaced on the maps of the ground
between
them
was
difficult.
Contours spaced every 5 mph would make the estimation of the
contour velocities at each location
more
accurate.
If
much
easier
and
a method could be devised to construct
continous contours, it may be very effective indeed.
the
maximum
value
much
of
increased so that all
the
gradient
ground
wind
Also,
velocity needs to be
station
locations
are
error
the
bounded on each side by velocity contours.
However, a more significant
correlation
is
related
to
source
of
in
the fact that the hotwires are
- 81
-
measuring the flow at a height different to
the particles.
the
can
be
of
Irwin's instrumentation appears to be a good
solution to this problem, since the height of
tube
height
easily
the
vertical
In addition to reducing the
varied.
error due to differences in height, such an instrument would
allow
testing
the
of various size particles, to determine
which size and density most accurately models the gusts that
are dangerous to pedestrians.
It may be that the more physically similar erosion type
of
study
yields more accurate results than a hotwire study
because it is physically similar to what happens full scale.
However,
since most full scale data is recorded in the same
manner as the data recorded in a hotwire type
correlation
procedure
wind
studies.
study,
a
useful, in that it allows one to
is
access the reliability of the
ground
of
In
wind
the
erosion
technique
for
meantime, the wind erosion
technique is a useful supplement to the hotwire type methods
currently employed.
- 82
-
REFERENCES
1.
R. M. Aynsley,
W. Melbourne,
B. J. Vickery,
Architectural
Aerodynamics, Applied Science Publishers, LTD, London, 1977.
2.
S. Murakami, K. Uehara, K. Deguchi, "Wind Effects on
Pedestrians: New Criteria Based on Outdoor Observation
of Over 2000 Persons", Fifth Int. Conf. on Wind Eng.,
Fort Collins, CO, July 9-14, 1979.
3.
N. Isyumov and A. G. Davenport, "Ground Level Wind Environment
in Built-up Areas", Proceedings of Wind Effects on Buildings
and Structures, 1975, London.
4.
J.O. Hinze, Turbulence, McGraw-Hill, 1975, pp 46,47
5.
S. J. Beranek and H. Van Koten, "Visual Techniques for the
Determination of Wind Environment", Journal of Industrial
Aerodynamics,
6.
No. 4, 1979, pp. 295-306.
I. Van Der Hoven, "Power Spectrum of Horizontal Wind Speed
in the Frequency Range from 0.0007 to 900 Cycles per Hour",
Journal
of Meteorology,
Vol.
14, p 16, 1967.
7.
W. H. Melbourne and P. N. Joubert, "Problems of Wind Flow at
the Base of Tall Buildings", Proceedings fo Wind Effects on
Buildings and Structures, 1971, Tokyo.
8.
J. Gandemer, "Wind Environment around Buildings: Aerodynamic
Concepts", Proceedings of Wind Effects on Buildings and
Structures, London, 1975.
9.
J.C.R. Hunt, E.C. Poulton, and J.C. Mumford, "The Effects of
Wind on People; New Criteria Based on Wind Tunnel Experiments",
Building and Environment, Vol.ll pp15-2 8 , 1976.
10.
F.G. Durgin, "Some Methods and Techniques Used for Ground Wind
Studies at the Wright Brothers Wind Tunnel, M.I.T.,", reprinted
from Proceedings: The Third National Conference - Wind
Engineering Research, 1978.
11.
S. Radovsky, and F.H. Durgin, "Wind Tunnel Study of Pedestrian
Level Winds at Battery Park City, New York, New York", Wright
Brothers Wind Tunnel, M.I.T., WBWT-TR-1097, June 1976.
12.
A.G. Davenport, "The Dependence of Wind Loads on Meteorological
Parameters", Paper No. 2, Proceedings of the International
Seminar on Wind Effects on Buildings and Structures, National
Research Laboratory, Ottawa, Canada, September, 1967.
- 83
-
13.
G.S. Campbell, and N.M. Standen, "Progress Report II on
Simulation of Earth's Surface Winds by Artificially Thickened
Wind Tunnel Boundary Layers", Laboratory Technical Report
LTR-LA-37, National Research Council of Canada, Ottawa, Canada,
July,
1969.
14.
A.G. Davenport, and N. Isyumov, "The Application of the
Boundary Layer Wind Tunnel to the Prediction of Wind Loading,
Proceedings of International Seminar on Wind Effects on
Buildings and Structures, Ottawa, Canada, September 1967.
15.
P. Sachs, Wind Forces in Engineerinq, Pergamon Press, Oxford,
1972.
16.
F.H. Durgin, "Measuring facade pressures at the Wright
BrothersMemorialWind Tunnel,"Proceedings
of the Fourth
U.S. National Conference on Wind Engineering Research,
July 1981, Seatle.
17.
R. Grip, and F.H. Durgin, "A Study of Ground Winds for the
New Hospital in the Health Sciences Center of the University
of Minnesota", WBWT-TR-1144, 1982.
18.
P.A. Irwin, "A Sensor for the Rapid Assesment of
Pedestrian Wind Environment", Proceedings of the Fourth
U.S. National Conference on Wind Engineering Research,
July 1981, Seattle.
19.
E. Simiu and R.H. Scanlan, Wind Effects on Structures,
John Wiley and Sons, NY, 1978.
- 84
-
Table 5.1 -
Angle Between Contour and Direction
of flow at the Ground Plane (Degrees)
Location
Angle
Location
Angle
1
0
10
0
2
75
11
45
3
90
12
70
4
90
13
100
5
150
14
135
6
150
15
180
7
180
16
135
8
180
17
10
21
90
31
90
22
60
32
60
23
90
33
90
24
120
34
120
25
120
35
135
26
180
36
180
27
150
37
135
41
0
51
0
42
45
52
90
43
135
53
135
44
150
54
180
45
150
55
135
-
85
-
Table 6.1 -
University of Minnesota -
Contour Gradient
Velocities for Different Locations and
Wind Directions
Existing Building:
Location
N
NE
E
SE
S
SW
W
NW
1
42
32
30
60
48
35
45
43
2
25
28
27
60+
35
30
38
42
3
25
28
30
60+
35
25
35
38
4
25
32
37
60+
38
30
32
38
5
37
39
40
60+
42
35
27
37
6
42
35
28
50
44
32
25
32
7
42
25
25
25
44
31
25
30
8
NA
25
28
30
45
28
45
37
9
NA
32
35
29
50
35
45
35
10
40
40
35
30
42
28
25
34
11
44.
43
45
32
35
40
35
38
12
25
38
60+
32
50+
45
50+
40
13
32
32
60+
28
50+
45
50+
45
14
45
50
40
27
18
31
32
28
15
62
30
38
39
25
37
38
34
16
60+
60+
60+
60+
52
41
42
40
17
60+
60+
60+
60+
50+
35
38
43
18
60+
60
60+
55
35
40
45
37
19
60+
39
60+
50
27
35
38
30
20
60+
42
45
42
30
28
45
40
- 86 -
Location
N
NE
E
SE
S
SW
W
NW
21
60+
30
50
36
25
25
44
34
22
60+
47
60+
45
45
35
48
45
23
60
58
60+
40
55
32
42
55
24
35
31
60
30
55
41
40
45
25
45
25
50
38
45
40
45
25
26
42
38
52
45
35
40
42
44
27
41
35
48
38
35
38
45
42
28
55
28
34
29
25
35
52
48
29
40
32
34
NA
32
31
42
46
30
33
30
NA
NA
25
NA
38
39
31
56
35
NA
NA
32
31
45
50+
32
65
45
NA
NA
42
30
42
50+
33
65
40
NA
NA
40
32
35
50
34
61
35
NA
NA
45
32
35
50
35
61
42
NA
NA
45
32
35
45
36
61
42
NA
NA
45
32
35
45
37
60
60
NA
40
40
35
35
NA
Proposed Building:
38
42
41
38
50+
45
38
52
50+
39
37
28
35
50+
45
38
35
48
40
37
25
35
50+
45
30
35
38
41
37
28
35
50+
45
38
30
40
42
45
40
38
52
45
37
28
38
43
55
50
42 30-50
45
34
25
35
-
87
-
W
NW
N
NE
E
SE
S
SW
44
50+
32
25
25
45
32
28
35
45
50+
45
35
35
45
38
49
35
46
50+
45
42
35
45
48
48
35
47
50+
40
30
38
43
28
32
35
48
55
50+
38
30
50
30
40
45
49
35
50
50+
42
50+
50+
50+
50
50
30
40
50+
38
50+
50+
50+
50+
51
50+
50+
48
28
35
30
38
25
52
50+
38
38
38
38
40
40
3.5
53
50+
49
52
40
42
50+
44
40
54
50+
53
50+
52
50
50+
35
35
55
50+
45
50+
50+
48
38
44
52
56
50
45
50+
50+
49
48
50+
50+
57
35
45
45
45
49
50+
50+
35
58
45
45
52
50+
50+
50+
50+
42
59
50+
52
50+
50+
45
32
32
50+
60
50+
50+
50+
50+
44
30
50
50+
61
35
40
40
NA
NA
32
25
50+
Location
-
88
-
Table 6.2 -
City of Buffalo, NY -
Contour Gradient
Velocities for Different Locations and
Wind Directions
Location
N
NNE
S
1
39
2
40+
38
29
28
40+
40+
5
30
35
35
32
6
31
31
35
36
40+
40
40+
29
36
- 89
35
-
28
40+
27
40+
40+
35
NA
27
35
38
28
NA
33
25
40+
33
35
38
38
30
39
37
24
27
30
35
35
40+
30
40+
30
31
30
30
35
38
32
40+
40+
40+
35
30
40+
30
24
33
24
34
33
40+
39
36
35
35
40+
40+
.34
36
36
NNW
40+
23
29
25
40
40
40+
8
40+
29
40+
34
31
36
40
33
40
40
7
35
NW
40+
24
29
SSE
WNW
31
37
SE
40+
35
40+
34
W
NA
33
40
ESE
40
31
29
31
35
34
28
E
WSW
40+
28
27
4
40
40+
24
3
SW
SSW
41
ENE
NE
40
36
32
26
Figure 1.
Dwelling in Hyderabad, India
-
90
-
-
Wind Direction
•2..
Figure 2.
Result of Velocity Gradient Flow Around Buildings
- 91
Ve1j
o
o
V
&
(n
Qz
U)
c
4
0O
c
o0
0
ur
n
C
.:
0
C
J
Q
0
o
o
o
O
C
..
.[(3S/W) vJ 133dS A!9D3N3
-
92
-
4
0
2
L
4
f-4
C
3
fr
50
si
-4
-4
-H
I-)
-o
-H
-Li
5:
as
o
c12
£
509
4-
Iz
-
93
-
lii
-J
C)
m
Z )
LUI
=,C)
D :
C/)
r.(
LI
0)
c
0ZE
E
C
' :
or
Eq
U
H,
Wa
(no
I)O
r
.4--
W-
Ll
oo'
4-4
0T~
3:
0
r_
0
CZ
tk
co
41-4
0
-14-iO
>
co
0
j
4(1)
13
3
.4
tk
-1PM
-
94
-
Figure 6a. Hotwire Stand at Gradient Height
Figure 6b. Wind Tunnel Test Section, Looking Upstream
-
95
-
..-f
I
t5mm.
11.
2mm
7
X
2mm.
mI
.5mm.
Figure 7.
Particle Size and Shape
-
96
-
Figure
.
Instrxlmentation
-
97
- Hotwire Test
-
C
>
0
t5
-
180
90
0
-90
-180
-c
-180
Figure 9.
-90
0
90
180
Variation of Hotwire Measurement with Wind Direction
-
9
-
50
I
*
Average ~ and
1,2 Ft
I
(pitot rake)
40
30
U 20
.c
10
0
U/Ug
Figure 10.
-
Simulated Earth's Boundary Layer
99
-
Anf
U
m,
o
Brookhaven, USA.
hg=130 0 ft.
0
40
-
hg= 900 t.
A
=.28
Sale, Austalia
A
A
A
Measured
d = .16
in wind tunnel
A
30
-
A
e)
20 _
A,
C
A4
A
10
A
a
QI [*E~· 3
I
01
0
3
a
l
0.2
0.1
%.1
Figure
11.
Longitudinal Turbulence Intensity
-
100
-
G
0
CU
In
/
a
/
/
/
a
"-
/
00 00
II
II
O
O
II
II
C00~
In
clo
In
0
-0)
a
Q
C JJ
C.
C
11I
r 0
Ii
Iii
4J*
-
0
-p
u,
<9
4)
lO
SU.
0
In
cu
1,
I
0 0'0
02
I
-
I
!
0 0 T-
I
0 T((u)s
-
101
-
00'a0 Bo1
I
sa
B
9*
a
a
" '"'"
;' ;
r·
Figure 13.
Wind Erosion Test
-
102
-
4
a
V
-
Figure 14 .-.
103
4,;_Lte
-
Test
Figure 15.
Typical Hotwire Signals
-
104
-
· .......
-i
sn
I%.
~
I.-
_
ffE
·
,~
A"-""
.M
.
_
_-
l
vo
_--_LI
_-T
I.__-1
1.Il
r~
,.~
,~~~~
Wind Direction
Vgrad = 10 mph
Vgrad= 15 mph
Vgrad = 20 mph
Vgrad= 25 mph
Vgrad= 30 mph
Vgrad = 35 mph
.e
ee
."e
Vgrad = 40 mph
Vgrad = 47 mph
emeem
e_
Vgrad = 50 mph
Figure 16.
.
-
Contours - h=1.0,
105
9 = 0 Degrees,
-
Run
1
'Allt^
_mm
Vgrad= 20 mph
Vgrad= 25 mph
Vgrad= 30 mph
Vgrad = 35
.....
~-
mph
....Vgrad = 40 mph
*.-
.*
Wind Direction
Vgrad = 10 mph
Vgrad= 15 mph
"-
Vgrad= 47 mph
Vgrad = 50 mph
Figure 17.
Contours -
-
106
h=1.O,
-
= 22.5 Degrees
·~~~~~~~~~~~~J
~/~ ~ .
===_
=
uxit "v'
MI
,.. .....
N
Vgrad = 10 mph
Vgrad = 15 mph
Wind Direction
Vgrad = 20 mph
Vgrad= 25 mph
Vg rad = 30 mph
"---
Vgrad= 35
.......
....
..
-- J
mpn
Vg rad = 40 mph
Vgrad= 47 mph
Vgrad = 50 mph
Figure 18.
Contours - h=1.O,
-
107
-
e = 45 Degrees
-r^BP
nE
._
I
AX
=
I
_
Vgrad:~
= 15 mph
.
,
Vgrad=
Vg
rad = 35
40 mph
mph
Vgrad = 47 mph
-
Vgrad = 50 mph
Figure 19.
Contours - h=1.0,
-
10
-
0 = 0 Degrees,
Run 2
"
--
~
_
,
_
!
_~
_..
M
,
7
k
L z t _ _ _ S b
?za>b
~~~~~~~~.'
"~"
r-~it'
rli>;F
W _ _ __2
Vgrad = 10
mph
T . 1_
in
NGC
' ,.t,
__ v7_X
-1
t<w
- v
I
% ....
.,
wW:;S4-
k,~i
I~~~~~~-
,·
Vgrad=
,,--{
.
I~;1 1hE
I
___ _
amm
S--T
_--
~~~~_
-.
-
j
~
_ _
·
%... -y
Wind Direction
15 mph
Vgrad= 20 mph
Vgrad= 25 mph
_._
i_,i1~._llBel
Vgrad= 30 mph
Vgrad = 35 mph
ee4 ......
4e(e·ee. .
Vgrad = 40 mph
M· eealee·
Vgrad = 47 mph
Vgrad = 50 mph
Figure 20.
Contours - h=1.0,
-
109
-
_ ,
8 = 0 Degrees, Run 3
Wind Direction
0 = Stagnation Points
Figure 21.
Contours
- h=0.25,
-
110
-
8 = 0 Degrees
* = Stagnation
Figure
22.
Contours - h=0.5,
-
111
Wind Direction
Points
-
= 0 Degrees
r-
·
Figure 23.
Stagnation
Points
Contours - h=0.75,
- 112-
Wind Direction
e = 0 Degrees
Wind Direction
*
Figure 24.
5
Stagnation
Points
Contours - h=1.,
A
-
113
-
= 0 Degrees
__
0 = Stagnation Points
Figure 25.
Contours - h=1.25,
-
114
-
J
im
Wind Direction
G = 0 Degrees
d
* Wind Direction
· - Stagnation Points
Figure 26.
- hsl.5,
CoQtur
-
115
-
e =
0
Degrees
0.7
P1
0.6
I
0.5
0.4
*4
4)
LL.
0.3
4)
0
C
a'
a
0.2
0.1
-
_
I
0.25
}
0.5
1.0
0.75
J
1.25
|~~~~~~~~
1.5
Building Height - Feet
Figure 27.
Distance of Stagnation Point from WindwardFace
-
116
-
2,8
I
2A
=0.5
2.0
m
4 .
U-
1.6
-
I
0
o
0
1.2
=0.25
0)
0.8
0,4
-
_
/
No
1
A
___
__
20
25
I
I
30
35
...
40
Gradient Velocity - m.p.h.
Figure 28.
Scour Area for Different
-
117
-
Building Heights
*
Vgrad= 20 mph
* Vgrad= 25 mph
A Vgrad= 30 mph
+ Vgrad=35 mph
--
2.8
2A
2.0
(.
1.6
(I
0
0
1.2
<5
0.8
0.4
l
a0
0.25
0.5
0.75
Building Height -
Figure 29.
I
I
II
1.0
1.25
1.5
Ft.
Scour Area for Different Gradient Velocities
-
11
-
m
m
'Wind Direction
h = 0.25 Ft.
rxxslxlXx h = 0.5 Ft.
h = 0.75 Ft.
h=1.0 Ft.
h 1.25 Ft.
.............
h = 1.5
Ft.
Figure 30.
Contours - Vgrad = 20 mph,
-
119
-
e = 0 Degrees
a---m=
h = 0.25 Ft.
x,,=srx~,m
h = 0.5
--..--
h
-- - ............
h-= 1.0 Ft.
h=1.25 Ft.
h = 1.5 Ft.
Wind Direction
Ft.
0.75 Ft.
Figure 31.
Contours - Vgrad = 25 mph,
-
120
-
8 = 0 Degrees
46
m
AS
w-
la xxxuix
-.-.-
h = 0.25 Ft.
h -=0.5 Ft.
h = 0.75 Ft.
h = 1.0
--
...........
Figure
--
Wi
Ft.
h=
h 1.25 Ft.
h = 1.5 Ft.
32.
-
Contours - Vgrad = 30 mph,
121
-
= 0 Degrees
ind Direction
rr,
-
L
i,
-
·-
L
I
r
4jrIC
-…-Ll
I
LI
I.
l-l
-l-L
I.I
--
_!__ _I 1 '_I'
-1
'_
.,
h = 0.25 Ft.
x
.
mXjr
h 0.5
Wind Direction
Ft.
h 0.75 Ft.
h= 1.0 Ft.
h = 1.25 Ft.
.............
h = 1.5
Figure 33.
Ft.
Contours - Vgrad = 35 mph,
-
122
-
e
= 0 Degrees
-
_
I,,
in~
h = 0.25 Ft.
^rlgxxxxAx( h = 0.5 Ft.
...
.
-- -.............
h = 0.75
h =1.0
h = 1.25
h = 1.5
Figure 34.
= Stagnation Points
Wind Direction
Ft.
Ft.
Ft.
Ft.
Contours -
Vgrad = 40 mph,
-
123
-
= 0 Degrees
2.8
I
2A
0
1.8
U.
A
I
=
0 Degrees
=
22.5 Degrees
=
45 Degrees
0
U)
1.2
0
au
C
0.8
OA
20
!
I
!
I
25
30
35
40
Gradient Velocity - m.ph.
Figure 35. Scou: Area for Different Wind Directions
-
124
-
I
0
Figure 36.
z Stagnation
Contours -
125
Wind Direction
Points
h=1.0,
-
e
= 22.5 Degrees
-
---
-
-
-
--
A
* = Stagnation Points
Figure 37. Contours =
-
-
126
h=1.Q,
O
-
\Wind Direction
= 45 Degrees
0 = Stagnation Points
Figure 38.
Contours -
-
127
Final Run
-
Wind Direction
*
'Locations
*
Additional locations tested
tested on contours
l
Wind Direction
Figure 39.
Hotwire Locations for Simple Shape Building
-
128
-
Wind Direction
Figure 40. Average Velocity Coefficient
-
129
-
Contours
-
77
-m
-
-
-I
1
I
I-
-
3-
m-
I
i
Imm
OM
0-
S
m
- IvT
.L e ; - -
I
I-`
I
VI if
mm
11-
I
-
4a
*ft
4&
I
--A
A-
I
d I
F
--4Ir
.3b L
0-1 W
II
i-7
.
I
II
A
I
i
N-
b.-
1
-CI
-qI
I #IN-
,---"41
i
'I
--
'I
7-
-1
11
i
II
----
i
.-.
II
I
-
I
I
Ir
7-
H
H
!
F
Ir
L
I
lir
L_
E2
i
i1
ii
i
--
i
L-
F
-
, Local direction of flow
I,
L-
.
-
Lo
-
--. m/
t
-- ---
,-
Wind Direction
Figure 41. Local Direction of Flow
-
130
-
..
d
rr
--
Wind Direction
Figure 42.
-r
RMS Velocity Coefficient Contours
-
131
-
fob
Wind Direction
Figure 43.
60 Hertz Peak Velocity Coefficient Contours
-
132
-
,,m
O
N
O
^~
0
c
0
0
0
I.
Cd
o
O
N
u
,
o
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>
I )
U-0
Q
C
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a
CD
,
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a)
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r
c
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O
O
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o
Q)
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oo
Et
oQ~~~~~~~~~~~~~~~~~~~~~~~~~~~
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a Q
t-
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U
I
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v
o
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o
lua!el;aoo
X~!ola
-
133
-
C
o
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o
0
ok
o
C)
o
N
tN
N
W
0
I
0
>.
Ca
CC)
0
N
01o
L
>
4!
Xd
N~~~P
0
I
L
0
CO
(0
,
-
0
t
0
I
0
lueio!Jeo ,OleA
-
134
-
¢,
0
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0
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t,
co
4n
0
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CL
(O
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r£
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PO~~
rl
dl
i
4)
0
L-
0ua 0 ! 0
I
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I
o
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O
,U91!;.90e APl.O1eA
-
135
-
06
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C
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,
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O
O
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-
136
-
h
-
-
I
I
I
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I
I
'-
,
1
C
o
C
o
C
a
0
o
0 0
0
0
o 0
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0
0
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o
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0
o))VV
C)
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Cd
U
N
,-
I ,NS
I
.
o
a)
0
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0
C,
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I
O
I
I
U,)~
t~ic
o
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IN
0o uae!i!3a1o
uo!eijBA
-
137
-
I
I
0.
I
0o
o
*A
1.Z
I
9.
,
*
11~~~~~.
1.0
I
/
a
f
S.a
a~~~~~'
..
I
0.8
100 Hz. k=4
60 Hz.
-
._
40 Hz. k=3
0.6
0
C)
k=2
10 Hz.
0o
0
0.4
4 Hz. k=l1
1 Hz.
Avg.
0.2
R.M.S.
0.0
I
1
I
2
3
I
I
I
I
4
5
- 6- .
7
Location Number
Figure 49.
Velocity Coefficients - Locations 1-8
-
138
-
8
p
1.2
1
'
-
/
Zp
/
J
,.
--
-
1.0
100 Hz.
0.8
,60 Hz.
k=5
C)
,-
k=4
0.6
.)
00
k=3
0
or
10 Hz.
OA
k=2
4 Hz.
k=1
0.2
_
1 Hz.
Avg.
.,4
U
0.0
I
I
10
11
__1
__ ___ 14
I
I
12
13
-I
-
I
. 15.
-
I
i
__~~~~~~~I
17
Location Number'
Figure 50.
Velocity Coefficients - Locations 10-17
-
139
-
R.M.S.
I,
1.Z
W
100 Hz.
k--5
1.0
-
60 Hz.'
k=-4
0.8
-
k=3
C
10 Hz..,
0.6
0o
0
4 Hz. k=2
C.
U
0
0.4
1 Hz. kl=1
-
Avg.
0.2
_
R.M.S.
w-
0.0
I
I
I
I
21
21
23
24
I
25 -
I
I
26.
27
Location Number
Figure 51. Velocity Coefficients
-
140
-
- Locations 21-27
.----, - k=5
'a,
.
1
I.L
m
-
I._
_
k=4
1.0
IN
60 Hz. i
100 Hz..'
k=3
0.8
k=2
10 Hz.
._
4.-
0.6
4 Hz.
I
k=1
.4-
0
0
1 Hz.
o
0
m,
0.4
Avg.
,
0.2
0
0.0
I
31
1
32
I
33
_I
I
34
Location
-
Figure 52.
I
35
R. M.S.
!
36.
37
Number
-
Velocity Coefficients - Locations 31-37
-
141
- \
d
du
1..
I
k 4
100 Hz.
1.0
I
60 Hz.
k=3
k2
10 Hz.
0 0.6
4 Hz.
.)
k=1
C)
0
o
1 Hz.
0.4
Avg.
0.2
II
0.0
R.M.S.
l
41
I
i
42
I
- 44
43
I
45
Location Number
Figure 53.
Velocity Coefficients - Locations 41-45
-
142
-
/N
I
/
/
1.2
k=4
100 Hz-
1.0
60 Hz.
k=3
0.8
10 Hz. k=2
0
,_
0
0.6
4 Hz.
I·
U
0
k=1
>C
,m
_o
0.4
Im
0.2
m
0.c - ·I
Avg.
R.M.S.
I
51
i
52
I
53 -
I
. 54
I
55
Location Number
Figure 54.
Velocity Coefficients - Locations 51-55
- 143
o
- 0~~
O
I
N
I1
'4
O
u~
ZI
r
0
0
r
0
oo
r
,u
xN
C14
0
r-4
r
0)
O
>
04
CM
N
L
C
v
. u-
44
E
R12)
v
N
I
I
o.
"'
c
0
i
(O
d
Jo:e-
-
)1
144
-
I
N
-1-4
0
I
I
I
I
C
0.
0
0
.0
0
0
-J
00
.J
-I
-I
0
CQ
0
A0
.4
0
c
0
*o0
a
Ol
O
o
CC~
I
N
_
L
a
0-f
qJ
)>
o
0
n
'4.~
CoQ
I
U,
6
I
,
0
I
I
I
I
6
0
0
0 lua!O!ao3
uo!le!ieA
-
145
-
0
0
9)
o
0
.LJ
00
C.
C'
V~~~~~~~~.-
0
N
0
LA,
I
hZ~~~~i~~
I4
.0
0
0
(0
co
O
v,~~~~U
4-i
u
0r
U)
I
9-
0
L
(N~
I
I
,
I
I
I
-
0
0
0
0
-
146
-
~~~(
)
0
0
3
o
1-4
0
0
!
o0
CO
V)
1-4
C
0
L_
0,
4)
.
V
0
0
1
0
co
0)
A)
L
4)
C)
4,
V
a)
C
C
0
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o
UO
1*
(n
a,
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0'
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0
m
o
C
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0
C
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-
14 7 -
30
14A
I
11A
13A
12Z
10
A17
32E
33E]
220
4A
2A
1A
._
341
350
5&
370
6A
25I
3A
310
53
520
420·23
20
510
26 54
8r
27
24·
15
'7' 36
440
450
21
410
o
0
38r
O
280
Contours:
r
Q4
0.
10
A
Locations
A
Locations 10-17
r
1- 8
Locations 21-27
Locations 31-37
O
0
Locations 41-45
Locations 51-55
I
__I
I
I
I
I
0
30
60
90
120
150
Angle -
Figure 59.
__ Ia
180
Degrees
60 Hertz Peak Velocities for Different Angles
- 148
-
Contours:
A
Locations
1- 8
Locations 10-17
-
-
0.15
I
*
Locations 21-27
O
*
0
.Locations 31-37
Locations 41-45
Locations 51-55
m.
£
._
0.10
._
.
O
Z4)CD
Z
0
U
005
U
I
0
a
a
0.5
1.0
-~~~~~~~~~~~
A
A
iS
B
I
a
2.0
2.5
kangle
Figure 60.
Coefficient of Variation
-
149
-
-
k angle
a
3.0
Contours:
A
Locations
A
Locations 10-17
1- 8
Locations 21-27
o
Locations 31-37
0.10
O
o
.
0
.O
To
0.05
0
I
I
I
I
I
I
0
0.5
1.0
1.5
2.0
2.5
kpile
Figure 61.
Coefficient of Variation
-
50
-
-
k pile
a
3.0
CcnntnJ,
~..
_-·VU:
A
H
Locations 1 - 8
Locations 10-17
---6
I
0
.,
0
Oo
0
l
&6
0
-.
kDist
(kpile
0
2.0
2,5
= 1.5 )
Figure 62. Coefficient
of Variation - k
dist
-
151
-
3.0
30
II
__
0
20
I
Il
I
to
O
0
I
4,
a
-.3a,
10
S
a
m
i
p
0
I
I
|
-
-
20
30
25
Gradient Velocity - m.p.h.
Figure 63.
Variation of Peak Velocity with Gradient Velocity
-
152
-
-
-
00
C4
0U,
00
o
)
.
0
_)
C)
r
N
(N
0
C,
U
CZ
a
Cro
U.
0
00
0k
LL
(0
0
I
CJO
--
I
C
I
T
I
N
)I
Joe-j
-
53
-
0
0
-4
2_____
Wind Direction
TNorth
Figure 65.
University of Minnesota - Existing Bldg. - North
-
154
-
2 Wo
-'-/
F
.\
"I
IL
----------t
Z/
Wind Direction
North
Figure 66.
-
University of Minnesota - Existing Bldg. - Northeast
155
-
,
f
jL
i
I
i
---
NrTh·--
Figure67.
University of Minnesota
-
-
Existing
lrthWind Direction
Figure 67. University of Minnesota - Existing Bldg. - East
156
-
Northind Direction
Figure 68.
University of Minnesota - Existing Bldg.
-
157
-
- Southeast
'I
.
Nrt
Eisting
L-
Wind Direction
f
South
Bldg.
Figure 69.
University of Minnesota
Figure 69.
University of Minnesota - Existing Bldg. - South
-
158
-
-
)Y•Zx
J
I-
IL
'_
N
-s
-
Nr
70.
Figure
University of Minnesota
-
Wind Direction
Existing Bldg. -South
Figure 70. University of Minnesota - Existing Bldg. -Southwest
-
159
-
Y,
I-
JL
---
-,
---------
-
3Wind Direction
North
Figure 71.
University of Minnesota - Existing Bldg. - West
-
160
-
y -
-
L
.-
'
IL
1..
.·
--
\
72.
Figure
Figure 72.
University of Minnesota
-
Existing Bldg.
Wind Direction
-
Northwes
University of Minnesota - Existing Bldg. - Northwest
-
161
-
·V
Nodrth
Figure 73.
Wind Direction
University of Minnesota - Proposed Bldg. - North
-
162 -
...C
-
-'
I
JL
..
kK
Wind Direction
r North
Figure 74.
University of Minnesota - Proposed Bldg. - Northeast
-
163 -
J
t
iy.
-..
f .:--. .
I.
'
-
North
Figure 75.
Wind Direction
University of Minnesota - Proposed Bldg. - East
-
16.4
-
r
~,~ Wind Direction
North
Figure 76. University of Minnesota - Proposed Bldg. - Southeast
-
165
-
\J ( ,
3 ')
.o
' Wind Direction
T
North
Figure 77.
University of Minnesota - Proposed Bldg. - South
-
166
-
-J
1)
L
s
-
-
-
/
X
-
==
-
o,
- -
-JL
uWind
T\North78.
Universit\
Figure 78.
-
Direction
University of Minnesota - Proposed Bldg. - Southwest
- 167
-
3
Wind Direction
North
Figure 79.
Bldg. - West
University of Minnesota - Proposed
-
168
-
f
's
I L
}
N
N
North
Figure 80.
~--- "-
Wind Direction
University of Minnesota - Proposed Bldg. - Northwest
-
169
-
A
A
5.0
*
A
A /A
/A
4.5
/
?"
A
Al
A
a
a/
II&·1
A
&t
.
U
A
.
4.0
A
A
A
3.5
A
I
I
I
20
30
40
I.
50
Gradient Velocity - m.ph.
Figure 81.
Univ. of Minnesota - k Factors
-
1 70 -
60
A
35
A
a
A
A
30
a
A
A
/
IL
0
/
25 _
A
I
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Figure 82.
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Figure 84.
Univ. of Minnesota - k Factors (extreme value)
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Figure 85.
Univ. of Minnesota - Peak Velocities (extreme value)
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North
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Figure 89.
North
City of Buffalo, NY- Northeast
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Wind Direction /
Figure 90.
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City of Buffalo, NY - East Northeast
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Figure 91.
of Buffalo, NY - East
City
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Figure 92.
City of Buffalo, NY - East Southeast
-
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City of Buffalo, NY - Southeast
-
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Figure 94.
North
City of Buffalo, NY - South Southeast
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City of Buffalo, NY - South
-
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t
Wind Direction .orth
Figure 96.
City of Buffalo, NY - South Southwest
- 1S5 -
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Wind Direction
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DATA
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Figure 97.
City of Buffalo, NY - Southwest
-
185
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Wind Direction
/
North
Figure 98. City of Buffalo, NY- West Southwest
-
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Wind Direction
Figure 99.
North
City of Buffalo, NY - West
-
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North
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Figure 100.
-
City of Buffalo, NY - West Northwest
189
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North
Wind Direction
Figurel101.
City of Buffalo, NY - Northwest
-
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Wind Direction \
Figure 102.
Northwest
City of Buffalo, NY - North
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Figure 103. City of Buffalo, NY- k Factors
-
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Figure 104. City of Buffalo, NY- Peak Velocities
-
193
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Figure 105.
City of Buffalo, NY -
-
194
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Normalized Peak Velocities
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Gradient Velocity - m.ph.
Figure 106.
k Factors (extreme value)
Buffalo -
195
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Figure 107.
.
I
Buffalo -
-
196
.
t
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t
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40
Velocity - mLph
Peak Velocities (extreme value)
-
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Location Number
Figure 108.
Norm. Peak Velocities (ex. value)
Buffalo -
197
-
SECTION
STREET
:E
WINO
CONNECT
TO
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PRESSURE
TRANSDUCERS
AXIS Or
SYMMETRY
PLAN VIEW
V
Figure 109.
Omnidirectional Pressure Device for Measuring
Pedestrian Level Wind Speed [18]
-
193
-