Paper 27.1
Near-wall investigation of a streamwise vortex pair
by
D.D. Kuhl and R.L. Simpson2
Department of Aerospace and Ocean Engineering
Virginia Polytechnic Institute and State University
Blacksburg, Virginia 24061; USA
1
ABSTRACT
Simultaneous three-orthogonal component LDV measurements with a measurement volume on the order of 50 µm in
size were made in a turbulent boundary layer downstream of a pair of half delta-wing vortex generators. Coincident
instantaneous U, V, W components of the velocity were used to determine the mean flow, Reynolds stresses, and triple
products. Measurements below y+ = 5 were made and used to deduce the wall skin friction. Careful considerations were
given to the evaluation of bias and broadening effects on the data. Data for a 2-D turbulent boundary layer closely agree
with direct numerical simulation (DNS) results. All turbulence data satisfy the realizability conditions. This is the first
time that detailed near-wall measurements have been made in this type of flow. While large streamwise vorticity is
generated away from the wall, significant opposite sign vorticity is generated by the viscous interaction of the vortex and
the wall. Further analysis of this data set is found in Kuhl (2000).
T
y
v.g.
x
z
S
Figure 2: Experimental test set-up
showing suction slot S; boundary layer
trip T and vortex generator pair v.g.
Figure 1: 3-orthogonal-velocity-component
fiber-optic LDV head
Y
Y
v.g
Z
X
10
x (cm
)
15
20
[d is ta
nc e fro
m v.g
.]
25
30
4
2
-2
0
z (c m
-4
)
Figure 3: VW mean secondary flow vectors in 2
measurement planes
1
2
Graduate Assistant
Jack E. Cowling Professor
Z
2
4
6
8 10
12
x (c m 14 16
)
18 20
2 2 24
26 2 8
30
X
log (y+ )
5
4
3
2
1
0
-6
y (cm)
0
(Ωx x h)/Ue
0 .5
0 .4
0 .3
0 .2
0 .1
0
-0 .1
0
-0 .2
-0 .3
-0 .4
-0 .5
0
-2
-4
z (c m)
Figure 4: Mean streamwise vorticity for a
semi-span in log(y+) and z planes
-6