Wake Vortex Investigations by Means of
Stereoscopic PIV and 5-Hole Probe
H.P.J. Veerman1, F.L.A Ganzevles1, K. Pengel2
1
NLR, National Aerospace Laboratory, Anthony Fokkerweg 2, 1059 CM
AMSTERDAM, PO. Box 90502 1006 BM AMSTERDAM, the Netherlands
2
DNW, German Dutch Wind Tunnels, Voorsterweg 31, 8316 PR MARKNESSE,
PO. Box 175 EMMELOORD, the Netherlands
Abstract
The trailing vortex system behind a civil aircraft wind tunnel full-span model with
extended flaps and slats is studied using stereoscopic PIV and the 5-hole probe
sensor as flow measurement systems. The steady and unsteady wake vortex flow
characteristics were investigated and measurement results from both measurement
systems were compared against each other and an error assessment was made.
1 Introduction
The wake vortex system behind civil aircraft may have important implications
for following aircraft. In particular during take-off and landing phase of a flight
the strength of the wake vortex field has significant consequences for the aircraft
throughput and therefore on airport congestion and flight delays. The ability to investigate the dynamics of wake vortex fields in all their details is important to address this problem. Stereoscopic PIV (S-PIV), enabling planar steady and unsteady 3-component velocimetry, is considered a powerful tool that opens ways to
these investigations. Now that S-PIV as a novel non-intrusive measurement technique has become available for large-scale industrial wind tunnels it is interesting
to assess its performance and accuracy relative to the proven but intrusive 5-hole
probe sensor. For this purpose in August 2001 a measurement campaign was executed in DNW’s Low Speed Tunnel (LST) on a civil aircraft full-span model, the
Fokker 29-1-2 model, in high lift configuration.
The main measurement objectives of the experiment were the following:
• Absolute and independent verification of S-PIV vs. 5-hole probe measurement
results,
• Error assessment of S-PIV in the DNW-LST industrial wind tunnel,
• Assessment of the intrusive character of the 5-hole probe sensor,
• Investigation of steady and unsteady characteristics and spatial evolution of the
wake vortex field.
68 Session 1
2 Measurement Environment and Equipment
2.1 Wind Tunnel
The experiment was performed in DNW’s closed circuit low speed wind tunnel
LST (see Figure 1), which has a cross section of 3.0 × 2.25 m2 and a test section
length of 8.75 m with excellent visual accessibility through removable transparent
side panels. This low speed wind tunnel is known to have a remarkably low free
stream turbulence of only 0.025%. The maximum wind speed in the empty test
section is 80 m/s; all tests in this project were performed at 60 m/s and 0 m/s.
Fig. 1. DNW-LST low speed wind tunnel.
2.2 Aircraft Model
The F29-1-2 generic civil aircraft full-span model was used. It consists of a fuselage and wings only; fins, tail and engines are not mounted. The model is
equipped with inboard and outboard flaps and slats. Figure 2 shows a sketch of
wing geometry and the flap and slat system. The measurements behind the two
high lift configurations, 7o and 18o angle of attack (α), concentrated on the vortex
emanating from a 35o deflected inboard flap. The aft part of this flap has an extra
flap partition, the inboard part has an extra deflection of 10o. The outboard flap
can be deflected either 5o or 15o.
The following two model configurations were tested (see Table 1 for details):
1. No slats mounted, inboard flap deflection 35-10/0°, outer flap deflection 5°, α =
7o.
2. Inner slat deflection 10°, outer slat deflection 20°, inner flap deflection 3510/0°, outer flap deflection 15°, α = 18o.
Aeronautics 69
Fig. 2. Sketch of the wing with available high lift devices
2.3 Five-hole Probe Sensor
An NLR designed and built rake equipped with 18 miniature 5-hole probes with
spherical heads is used (Ø 2.5 mm, probe pitch of 15 mm, see Figs. 3 and 4). Using this probe pressures are electronically scanned with pressure units placed inside the rake support sting yielding high data rates with on-line pressure calibration capabilities. The rake sting is mounted on a streamlined horizontal strut (Ø 70
mm) and is fixed to a Y-Z traversing mechanism (see Fig. 6). During measurements the rake is continuously traversed in the spanwise Y-direction (traversing
speed 5 mm/s), while taking measurements every second. With two intermediate
traverses a measurement grid of ∆Y∆Z = 5 × 5 mm2 was obtained.
2.4 PIV Equipment
A double cavity 2×380 mJ 10 Hz Quantel YAG-laser was used including beam
guidance mirror. The laser light sheet was inserted into the test section from
above, via a transparent Perspex neon light box in the ceiling of the test section.
The applied light sheet thickness of 8 mm was considered correct to accommodate
the relatively large cross plane flow component.
Two PCO SensiCam PIV cameras of 1280 × 1024 pixel resolution were applied. The double-frame rate of the laser/camera combination was 6 Hz. For each
70 Session 1
PIV camera a Scheimpflug adapter (from DLR) was used to compensate for leftright variations in depth of field.
For cross correlation of the images the PIVview software package, developed
by DLR, was applied. The stereoscopic reconstruction was realised by DLR and
DNW developed software. All 3 component velocity vector fields (including those
from the 5-hole probe) were stored in ASCII format, enabling NLR to analyse and
evaluate the results using Matlab.
Fig. 3. 5-Hole Probe geometry.
Fig.4. 5-hole probe rake (here equipped
with rubber caps).
3 Experiment Set-up and Model Configurations
3.1 Seeding aspects
The DNW-LST wind tunnel was globally seeded with DEHS, its benefits being
that this material is considered non-toxic and slowly evaporating, avoiding contamination of the facility.
Because the seeding may clog the tiny probe holes, small rubber caps must
protect them from seeding particles when the probe is inserted into the flow for
intrusive measurements (see Figure 4).
3.2 Spatial resolution and coordinate system
With the 5-hole probe rake a 5-mm spatial resolution was obtained, while its spatial accuracy was approximated to 2 mm. In the PIV processing the interrogation
areas (IA) in general were 32 × 32 pixel2. In order to obtain the same spatial grid
for both methods, this 32 × 32 IA must represent 5x5 mm2 in object space. With a
1280 × 1024 CCD pixel area this gives a PIV image area of 20 × 16 cm2. In this
set-up the pixel resolution is 0.16 mm and assuming a 0.2 pixel PIV resolution, a
resolution of 0.03 mm displacement is obtained.
A cross-plane displacement ∆X = 2 mm is used as the maximum displacement
in order to obtain a good correlation between first and secondary image, taking
Aeronautics 71
into account the camera depth of field and a laser light sheet thickness of 8 mm.
This 2 mm corresponds with about 10-pixel as maximum displacement. For a free
stream velocity of 60 m/s a 2 mm displacement corresponds to an optimal time
interval ∆t = 32 µs between first and second recording. During the measurements
∆t was set to 30 µs.
With 2 mm displacement corresponding to 60 m/s and a conservatively estimated PIV accuracy of 0.2 pixel, corresponding to 0.03 mm displacement, the estimated PIV velocity accuracy should be in the order of 0.9 m/s. However, error
assessment in post-processing will prove what accuracy was really attainable with
stereoscopic PIV.
Measurement locations ‘Xb’ downstream the model are given in units of wingspan (b = 1.3565 m) : Xb = (X-XMRP)/b with XMRP the position of the Model
Reference Point at α = 0°.
For both S-PIV and 5-hole probe measurements the same wind tunnel coordinate system was applied, having their origin at X = XMRP. Both co-ordinate
systems were correlated by means of a calibration grid.
3.3 S-PIV and 5-hole probe measurement geometry
For a good quality S-PIV result the PIV cameras had to avoid refraction effects
from the Plexiglas walls, but also avoid flow disturbance by cameras. Therefore
the PIV cameras looked through holes into the wind tunnel in this way minimising
the intrusive effects from the cameras.
Behind the model in high lift configuration three separate wake vortices
emerge: one from the inboard flap, one from the outboard flap and one from the
wingtip. De Bruyn et al [1] showed, that for a free stream velocity of 60 m/s both
outboard flap vortex and tip vortex perform a helical motion and subsequently
merge somewhere between Xb = 3 and Xb = 5, the distance depending on the angle
of attack and flap and slat deflections. It was decided that the most interesting part
of the flow is the outboard flap vortex area. Since the model fuselage was positioned in line with the centre of the test section, an asymmetric stereoscopic PIV
set-up was the consequence. Because the 5-hole probe measurement, which was
performed first, was a whole field measurement, it could be used also to locate the
area of interest for the S-PIV measurements, which had a field-of-view limited to
20x15 cm2. To avoid obstruction of the camera access to the light sheet by the
model, when measuring close behind the model, a ‘forward’ measurement geometry was applied. When measuring the intrusive effect of the 5-hole probe with
S-PIV, the ‘backward’ measurement geometry (see Figure 5) was used to avoid
camera obstruction by the 5-hole probe rake. The only drawback is that to avoid
obstruction from the model for those latter measurements ample measurement
distance to the model was required.
Given a CCD sensor dimension of 10.0 × 8.7 mm2 and an imaged area of 200 ×
160 mm2, a magnification of 0.05 is required. Using the focus criterion being 1/di
+ 1/do = 1/f, with di the distance in the image plane and do the distance in the object plane a required objective focus of f = 112 mm and f = 83 mm were calculated
72 Session 1
for both cameras. The best fitting objective lenses available were f = 100 mm and
f = 85 mm, which were selected.
Free flow = 60 m/s
1975 mm
1025 mm
PIV camera
f = 85 mm
PIV camera
f = 100 mm
F29-1-2
2
18
0m
m
1500 mm
MRP
8
24
0m
m
1500 mm
XB
tunnel
wall
5 hole probe
Fig. 5 Backward measurement geometry (Xb not to scale).
3.4 Measurement configurations
In order to meet the objectives of the experiment, the configurations for both SPIV and 5-hole probe as given in Table 1 were measured. In the column ‘Geo’ the
S-PIV geometry is given, ‘B’ for backward and ‘F’ for forward. During intrusive
effect measurements by S-PIV the 5-hole probe rake was not moving but fixed in
three positions, 5 cm left and right of the vortex core and at the vortex core, in order to be able to locate the intrusive effects relative to the probe position. Also an
S-PIV measurement with the 5-hole probe rake located close to the wind tunnel
wall was made in order to assess the influence of the horizontal strut.
Aeronautics 73
Table 1. Measurement configurations
Test
Ident
1
2
3
4.0
4.1
4.2
4.3
5
11
9
6
12
13
Active
sensor
5-hole
5-hole
5-hole
S-PIV
Xb
α
1
2.4
2.4
S-PIV
S-PIV
S-PIV
S-PIV
S-PIV
S-PIV
2.4
2.4
1
1
-
Outer
slat
0°
0°
0°
Inner flap
7°
7°
7°
Inner
slat
0°
0°
0°
7°
18°
18°
7°
-
0°
10°
10°
0°
-
0°
20°
20°
0°
-
35-10/0°
35-10/0°
35-10/0°
35-10/0°
-
35-10/0°
35-10/0°
35-10/0°
Outer Geo Remarks
flap
No model
5°
5°
B - Rake at wall
5°
- 5 cm left vortex
- center vortex
- 5 cm right vortex
B No rake
5°
B
5°
F
5°
F
5°
F No model
F V = 0 m/s
3.5 S-PIV versus 5-hole probe comparison approach
The 5-hole probe measurements were performed at two distances from the model
in the wake, i.e. at Xb = 1 and Xb = 2.4. To assess the intrusive effects and compare
absolute results from 5-hole probe vs. S-PIV the 5-hole probe was placed in well
known positions at a distance of Xb = 2.4 behind the model. For both measurements the angle of attack and flap and slat deflections were kept the same. The
flow field from these model configurations were measured by S-PIV with and
without the 5-hole probe inserted into the flow to determine the intrusive effects
from the rake. During S-PIV measurements with the rake inserted, the probe was
placed on three fixed and well-known positions to enable comparison and to determine intrusivity as a function of rake location and distance to the probe head.
Configuration 12 and 13 in Table 1 were measured for error assessment: by
measuring an empty wind tunnel at Vflow = 60 m/s both the wind tunnel flow reproducibility and S-PIV measurement accuracy could be assessed. The empty (but
well seeded) wind tunnel at Vflow = 0 m/s was measured as well. The flow distribution measured by reconstruction of the left and right vector fields should be essentially 0 in this configuration. It may therefore be considered as a set-up with a
well-known velocity field. In this measurement all deviations from 0 m/s in the
flow field found give an indication (in fact a lower limit) of the combined S-PIV
error contributions and spatial error distribution from the geometry set-up, calibration, cameras, cross-correlation and geometric reconstruction software altogether.
74 Session 1
4 The 5-hole Probe and S-PIV Measurements in DNW- LST
4.1 The 5-hole probe measurement and data processing
The 5-hole rake calibration [2] and data from an empty wind tunnel test prior to
the measurements were used to calibrate the 5-hole rake data. For the 60 m/s flow
regime, with the 5-hole probe a measurement accuracy of 0.5 m/s and 0.01° can be
obtained. However it should be emphasised that this accuracy is not valid for all
flow conditions: near and in the vortex cores or shear flow, a worse accuracy is to
be expected proportional to the ratio of probe diameter and velocity gradient.
Fig. 6 Model and 5-hole probe with attachment rod in DNW-LST.
4.2 Five hole probe measurement results
The measurement results obtained by the 5-hole probes are shown in fig. 7. The
grayscales indicate the out-of-plane velocity component relative to the free flow
velocity. Although the probe-measured area was larger, a 0.5 × 0.7 m2 area is
shown. As is visible in the figures, smooth, wide field, high quality results are obtained. In the velocity field measured at Xb=1.0 three wing related vortices are
clearly visible: the upper left is the wing tip vortex, the one in the middle emanated from the outboard flap, while the bottom right originated from the inboard
flap. Comparing this field with the one at Xb=2.4 shows that the inboard flap vortex moves downward, probably in a slow and wide helical motion with the other
Aeronautics 75
two, the wingtip and outboard vortices, which rotate around each other at a higher
pace.
The S-PIV measurement area that can be obtained is smaller, the configuration
that was defined permits an area of 0.15 × 0.20 m2. It was decided to concentrate
on the outboard vortex for the following reasons:
•
•
•
It interacts with both surrounding vortices and because of this its dynamics is
considered the most interesting to investigate;
This vortex is relatively weak and therefore accurately measurable for both 5hole probe and S-PIV. The wingtip vortex on the other hand is strong and expected to be depleted of seeding.
Fig. 7. 3C velocity map at α=7o for test conf. 2 at Xb = 1.0 (left) and test conf. 3 at
Xb = 2.4 (right) obtained by 5-hole probe. Grayscales indicate the out-of-plane
component.
4.3 S-PIV measurement
Two S-PIV measurement geometries were set-up, one in ‘Backward’ orientation
to enable intrusivity measurements and the other in ‘Forward’ orientation. The
measurement planes were placed at Xb = 2.4 and Xb = 1.0 wing span behind MRP
of F29 model. A rigid calibration grid, supported by optical benches was positioned during calibration in the test section, shearing the laser light sheet for the
highest possible accuracy.
All S-PIV measurements were performed in the order as given in Table 1. After
S-PIV measurements with the 5-hole probe installed in the wind tunnel, the same
measurements were performed again where only the probe was removed, optimally enabling the 5-hole probe intrusivity investigation. Finally, the model was
removed and with the S-PIV equipment kept in place the free flow at 60 m/s and 0
m/s was measured.
76 Session 1
4.4 S-PIV post-processing
For the S-PIV processing of the images a set of software programs and tools were
applied. The processing was divided into 4 steps:
1. Deriving the de-warping coefficients based on the warped grid images.
2. Iteration to improve de-warping coefficients by left/right correlation of the first
recorded images.
3. Deriving 2C vector fields of both left and right de-warped image pairs.
4. Stereoscopic reconstruction based on left and right vector fields and geometrical set-up of cameras and measurement plane in absolute tunnel co-ordinates.
All four steps were integrated with each other enabling definition of large batch
processing sessions. In [4] more details on the PIV processing can be found. Of
the 3C vector fields also the time-averaged fields (‘steady’) are determined. Also
avi movies are made, which, although the flow field was not time-resolved, provide an impression of the vortex dynamics.
4.5 S-PIV results
The S-PIV measurements show high quality results: only few spurious vectors appear and results are in general agreement with the 5-hole probe measurements.
Vortex cores measured with S-PIV were located at few mm distance from the
probe-measured positions for comparable configurations and providing comparable (steady) velocity fields for both the in-plane and out-of-plane components.
Details of S-PIV vs. 5-hole probe comparison are discussed in sect. 5.3.
Fig. 8 Time averaged 3C velocity field by S PIV at Xb = 1.0, α = 18o. The grayscales indicate the value of the out-of-plane velocity component.
In Fig. 8 the time averaged 3C velocity field of Test Configuration 6 is shown. In
the vortex field at Xb = 1.0 with the model at an angle of attack of 18o the interac-
Aeronautics 77
tion between the outer flap vortex and the wing tip vortex is visible. It also shows
that the wingtip vortex is smaller in size but with higher in-plane velocities and
larger velocity lag for the out-of-plane component.
5 Analysis and Discussion of Results
5.1 Wake vortex dynamics assessment
The vortex showed significant dynamical behaviour (see avi movie on CD-ROM).
An indication of this vortex dynamics can be given by means of a vortex core
scatter plot. The vortex core was defined as the position in the vortex area where
the interpolated velocities in the in-plane direction (U,V) are closest to zero. The
measured velocity field with a resolution of 5 mm was interpolated to a 0.5 mm
grid. The position where U2+V2 was smallest was the instantaneous vortex core
position by definition.
(a)
(b)
Fig. 9. Vortex core positions at α = 7o for Xb = 1.0 (a) and Xb = 2.4 (b)
Fig. 9 show the vortex core scatter-plots of measured instances. The scatter
plots show a significantly larger dynamic range of the vortex core positions at Xb
= 2.4 distance as compared to Xb = 1.0. It indicates that in the near field, the larger
the distance the stronger the dynamic behavior. Also the vortex core movements
show a preferred direction, with a vibration preference in the direction of the wing
tip vortex. This ability of dynamics assessment demonstrates an important advantage of PIV relative to 5-hole probe that lacks this ability.
5.2 Assessment of the 5-hole probe intrusive character by S-PIV
measurement
One of the objectives of the combined probe / S-PIV measurement campaign in
DNW-LST was to measure the 5-hole probe intrusive effects by means of S-PIV.
78 Session 1
In order to accomplish this the 5-hole probe rake was inserted into the flow at a
well-defined position. First, the 5-hole probe rake was positioned out of view with
respect to the S-PIV area (see Table 1). In this way the influence of the horizontal
strut of the probe could be assessed. Second, the 5-hole probe was positioned 5 cm
to the left of the vortex core position (looking backward), at the vortex centre and
finally 5 cm to the right. Those three rake positions were intended to find the
probe-induced effects at three different positions relative to the vortex. It was important to have the probe heads as close to the laser light sheet as possible, but not
too close in order not to catch too much stray light.
Fig. 10 Time averaged 3C velocity field by S-PIV of Test 4.1. The probe rake was inserted
into the flow, vertically at Y= -0.44 position, resulting in 10 disturbed areas close to the
probe heads. (Greyscales indicate out-of-plane component, white spots are caused by removal of false vectors.)
For configuration 4.0 (moved-aside probe rake) an interesting result was obtained. The time averaged vortex core centre was displaced downward by 18 mm,
well beyond the S-PIV position accuracy and resolution, which is in the order of 5
mm. It seems that the (Ø 70 mm) horizontal strut of the probe locally pushes aside
the flow in the downward direction.
Processing of the PIV images with the 5-hole probe rake in the PIV measurement area was much more cumbersome. The most interesting areas suffered from
pixel areas saturated by reflections. To enhance the result the PIV interrogation
areas were enlarged to 64x64 pixel to get as much information as possible, while
also various correlation techniques were tried for the optimal result. In configuration 4.1 (see Figure 10) ten areas were visible, vertically aligned at the expected
locations (close to the probe heads), where the flow was slowed down locally in
the order of 1 m/s.
Both effects show that there is evidence that the 5-hole probe introduces flow
distortions and measures its self-induced flow field, resulting into deteriorated
measurement accuracy.
Aeronautics 79
5.3 Comparison of steady S-PIV vs. 5-hole probe obtained velocity
fields
Although from a global perspective the steady velocity fields as obtained by SPIV and 5-hole probe are comparable, it is to be investigated whether this holds
also regarding the details of the measured flow fields.
Since the 5-hole probe measures only steady flow fields, time averaged velocity
fields obtained by a large set of S- PIV recordings are compared with 5-hole probe
obtained fields. Because of the dynamic character of the flow field two kinds of
time averaged S-PIV velocity fields are taken into account. The time averaged
fields where the mean value is calculated for the absolute positions in space are
called ‘mean’ fields, while those fields, where the average velocity value is calculated relative to the position of the vortex core are called ‘core-position aligned’.
So in the latter situation a (small) correction is made for the actual instantaneous
vortex core position relative to the average vortex core position. On beforehand, it
is expected that the ‘mean’ S-PIV field is more comparable with the 5-hole probe
field than the core-position aligned steady field. On the other hand, since fine
structures can be smeared out in the mean fields, the core-aligned S-PIV field is
expected to show more distinct details of the flow, if present.
5.3.1 Comparison of the out-of-plane velocity component
As is visible in Figure 11 and 12 the out-of-plane velocity component as obtained
by S-PIV shows a more smooth appearance than the 5-hole probe U velocity component. In the 5-hole probe field probe-geometry related artifacts are visible that
do not show up in the S-PIV obtained fields.
Fig. 11 Surface plot of the out-of-plane velocity component at Xb = 2.4, α = 7o for configuration 3, measured by 5-hole probe.
In the mean S-PIV U-component field already a peak broadening normal to the
direction of the wing tip vortex shows up. In the core position aligned Ucomponent field this broadening turns into two distinct peaks normal to the direction of the wing-tip vortex. It may be concluded that for the out-of-plane compo-
80 Session 1
nent, there are strong indications that S-PIV provides more accurate results when
investigating the small-scale structures.
Fig. 12 Surface plot of the out-of-plane velocity component for configuration 5, measured
by S-PIV, time-averaged (left) and core position aligned (right).
5.3.2 Comparison of the in-plane velocity components
The most straightforward way of comparing the in-plane velocity components for
S-PIV and 5-hole probe for a vortical structure is by comparing both in-plane vorticity fields. When investigating the vorticity fields, the S-PIV mean and coreposition aligned fields are smoother, less noisy than the vorticity field as obtained
with the 5-hole probe, as is shown in Figs. 13 and 14. It seems that especially in
high gradient environments probe-geometry related distortions of the vorticity
field, which are more pronounced in the direction parallel to the rake than normal
to the rake, show up clearly. Therefore again, there are indications that S-PIV provides for more accurate results when investigating small-scale flow structures,
than the 5-hole probe sensor does.
Fig. 13 Vorticity at Xb = 2.4, α = 7° for configuration 3 (5-hole probe).
Aeronautics 81
The double peak that was visible in the out-of-plane velocity field is not found
(as double peak) in the in-plane S-PIV vorticity field (see Figure 14), whereas the
5-hole probe in-plane vorticity field is too disturbed by probe-geometry related
artifacts to enable study of fine structures.
When comparing the mean S-PIV vorticity field with the core-position corrected
vorticity field it appears that the mean vorticity field is somewhat extended into
the direction of the preferred vortex dynamics (see Figure 14), whereas the vorticity field of the vortex that is corrected for its dynamic behavior, shows an almost
perfect circular shape.
Fig. 14 Vorticity at Xb = 2.4, α = 7° for configuration 5 measured by S-PIV, time-averaged
(left) and core position aligned (right).
6 Conclusions and Final Remarks
This experiment shows that both completely different measurement techniques SPIV and 5-hole probe give comparable results for the steady flow field. Getting
into details, there was evidence that S-PIV provides more accurate and smoother
results than 5-hole probe, which show rake-related artefacts. Applying S-PIV it
was feasible to measure the intrusive effects of the 5-hole probe: clear evidence
was found for the introduction of a vertical offset in the flow field introduced by
the downstream horizontal strut of the 5-hole probe system. Also all 10 visible
probe heads could be identified in the S-PIV measured flow field, although evidence was not as strong as for the ‘strut effect’, caused by the difficult PIV measurement conditions. Taking into account the fact that the 5-hole probe measures
self-induced flow phenomena, it is not surprising that S-PIV provides for more accurate results relative to 5-hole probe.
Concerning the unsteady characteristics of the flow field, interesting dynamic
features of the wake vortex were found, such as a direction of preference for the
vortex core vibration and a double peak in the flow lag of the vortex core perpendicular to the vortex core vibration.
As a final remark, although not being as accurate as S-PIV, the 5-hole probe
has the advantages that the set-up and also the processing is performed more
quickly, while a large flow field can be measured in a single run. Contrary, S-PIV
82 Session 1
is limited to smaller flow fields. So both measurement techniques can be considered complementary in usage: first, one measures the complete field by 5-hole
probe rake, to find the most interesting areas, after which those areas of highest
interest can be investigated in more detail and more accurately by (stereoscopic)
PIV.
Acknowledgement
This work has been performed under the EUROPIV 2 project: EUROPIV 2 (A
Joint Program to Improve PIV Performance for Industry and Research) is a collaboration between LML URA CNRS 1441, Dassault Aviation, DASA, ITAP,
CIRA, DLR, ISL, NLR, ONERA, DNW and the universities of Delft, Madrid,
Oldenburg, Rome, Rouen (CORIA URA CNRS 230), St Etienne (TSI URA
CNRS 842) and Zaragoza. The project is managed by LML URA CNRS 1441
and is funded by the CEC under the IMT initiative (contract no: GRD1-199910835).
References
[1] Flow Field Survey in trailing vortex system behind a civil aircraft model at high lift,
Anton C. de Bruin, et al., presented at AGARD Symposium ‘The characterisation and
modification of wakes from lifting vehicles in fluids’, Trondheim, 20-23 May 1996.
[2] Calibration of a Rake Equipped with 18 Five Hole Probes in the LST Test Number:
5632, NLR TR 96235, G.H. Hegen, NLR, 1996.
[3] Particle Image Velocimetry – A Practical Guide, M. Raffel, C. Willert, J. Kompenhans, Springer-Verlag, ISBN 3-540-63683-8, 1998
[4] Final Report on the stereoscopic PIV vs. 5-hole probe test in DNW-LST, H.P.J. Veerman, K. Pengel, F.L.A. Ganzevles, Europiv_2 _ TR_NLR_171002, 2002.