This study focuses on the detection and characterization of vortices in low Reynolds number separated flow over the elliptical leading edge of a low aspect ratio, flat plate wing. Velocity fields were obtained using the time-resolved particle image velocimetry. Experiments were performed on a wing with aspect ratio of 0.5 for velocities of 1.1 m/s, 2.0 m/s, and 5.0 m/s corresponding to chord length Reynolds numbers of $1.47×104$, $2.67×104$, and $6.67×104$, respectively, and angles of attack of 14 deg, 16 deg, 18 deg, and 20 deg. A local swirl calculation was used on proper orthogonal decomposition filtered data for vortex identification and corresponding vortex centers were tracked to determine convective velocities. The swirl function was also analyzed for its temporal frequency response at several discrete points in both the shear layer and in the separated recirculation region. A peak frequency was detected in the shear layer with a corresponding Strouhal number of approximately 3.4 based on the flow direction projected length scale. The Strouhal number increases with both angle of attack and Reynolds number. The shear layer convective length scale, based on the vortex convection velocity, is found to be consistent with the mean separation distance between vortices within the shear layer. This length scale decreases with increasing $Rec$.

1.
McCullough
,
G. B.
, and
Gault
,
D. E.
, 1951, “
Examples of Three Representative Types of Wing-Section Stall at Low Speeds
,” NACA Technical Note 2502.
2.
Carmichael
,
B. H.
, 1981, “
Low Reynolds Number Wing Survey, Volume 1
,”
NASA
Contractor Report No. CR-165803.
3.
Re
,
R. J.
,
Pendergraft
,
O. C.
, Jr.
, and
Campbell
,
R. L.
, 2006, “
Low Reynolds Number Aerodynamic Characteristics of Several Airplane Configurations Designed to Fly in the Mars Atmosphere at Subsonic Speeds
,”
NASA
Report No. 214312.
4.
Mueller
,
T. J.
, and
DeLaurier
,
J. D.
, 2003, “
Aerodynamics of Small Vehicles
,”
Annu. Rev. Fluid Mech.
0066-4189,
35
, pp.
89
111
.
5.
Torres
,
G. E.
, and
Mueller
,
T. J.
, 2001, “
Aerodynamic Characteristics of Low Aspect Ratio Wings at Low Reynolds Numbers
,”
Prog. Astronaut. Aeronaut.
0079-6050,
195
, pp.
115
142
.
6.
Broeren
,
A. P.
, and
Bragg
,
M. B.
, 2001, “
Unsteady Stalling Characteristics of Thin Wings at Low Reynolds Number
,”
Prog. Astronaut. Aeronaut.
0079-6050,
195
, pp.
191
213
.
7.
Bishop
,
R. E. D.
, and
Hassan
,
A. Y.
, 1964, “
The Lift and Drag Forces on a Circular Cylinder in a Flowing Fluid
,”
Proc. R. Soc. London, Ser. A
1364-5021,
277
, pp.
32
50
.
8.
Berger
,
E.
, and
Wille
,
R.
, 1972, “
Periodic Flow Phenomena
,”
Annu. Rev. Fluid Mech.
,
4
, pp.
313
40
. 0066-4189
9.
Mair
,
W. A.
, and
Maull
,
D. J.
, 1971, “
Bluff Bodies and Vortex Shedding—A Report on Euromech 17
,”
J. Fluid Mech.
0022-1120,
45
(
2
), pp.
209
224
.
10.
Yarusevych
,
S.
,
Sullivan
,
P. E.
, and
Kawall
,
J. G.
, 2005, “
Wing Boundary Layer Separation and Control at Low Reynolds Numbers
,”
Exp. Fluids
0723-4864,
38
, pp.
545
547
.
11.
Tinar
,
E.
, and
Cetiner
,
O.
, 2006, “
Acceleration Data Correlated With PIV Images for Self-Induced Vibrations of a Wing
,”
Exp. Fluids
0723-4864,
41
, pp.
201
212
.
12.
Cheng
,
M.
, and
Chen
,
B. K.
, 2007, “
A Numerical Study on Fluid Force Reduction of a Square Cylinder by Flow Control
,”
Fluids Engineering Conference
, San Diego, CA, Jul. 30–Aug. 2, Paper No. FEDSM2007-37025.
13.
Roshko
,
A
, 1954, “
On the Drag and Shedding Frequency of Two Dimensional Bluff Bodies
,” NACA Technical Note 3169.
14.
Abernathy
,
F. H.
, 1962, “
Flow Over an Inclined Plate
,”
ASME J. Basic Eng.
,
84
, pp.
380
388
. 0021-9223
15.
Burgmann
,
S.
,
Brücker
,
C.
, and
Schröder
,
W.
, 2006, “
Scanning PIV Measurements of a Laminar Separation Bubble
,”
Exp. Fluids
0723-4864,
41
, pp.
319
326
.
16.
Derksen
,
R. W.
, and
Rimmer
,
J.
, 2006, “
Aerodynamic Flow Simulation
,”
Int. Conference on Advances in Fluid Mechanics VI
, Skiathos, Greece, pp.
59
67
.
17.
Jeong
,
J.
, and
Hussain
,
F.
, 1995, “
On the Identification of a Vortex
,”
J. Fluid Mech.
0022-1120,
285
, pp.
69
94
.
18.
,
R. J.
,
Christiansen
,
K. T.
, and
Liu
,
Z. -C.
, 2000, “
Analysis and Interpretation of Instantaneous Velocity Fields
,”
Exp. Fluids
0723-4864,
29
, pp.
275
290
.
19.
Graftieaux
,
L.
,
Michard
,
M.
, and
Grosjean
,
N.
, 2001, “
Combining PIV, POD and Vortex Identification Algorithms for the Study of Unsteady Turbulent Swirling Flows
,”
Meas. Sci. Technol.
0957-0233,
12
, pp.
1422
1429
.
20.
Shinneeb
,
A. -M.
,
Balachandar
,
R.
, and
Bugg
,
J. D.
, 2008, “
Analysis of Coherent Structures in the Far-Field Region of an Axisymmetric Free Jet Identified Using Particle Image Velocimetry and Proper Orthogonal Decomposition
,”
ASME J. Fluids Eng.
0098-2202,
130
, p.
011202
.
21.
Agrawal
,
A.
, and
,
A. K.
, 2002, “
Properties of Vortices in the Self-Similar Turbulent Jet
,”
Exp. Fluids
,
33
(
4
), pp.
565
577
. 0723-4864
22.
Troolin
,
D. R.
,
Longmire
,
E. K.
, and
Lai
,
W. T.
, 2006, “
Time Resolved PIV Analysis of Flow Over a NACA 0015 Airfoil With Gurney Flap
,”
Exp. Fluids
,
41
, pp.
241
254
. 0723-4864
23.
Druault
,
P.
,
Guibert
,
P.
, and
Alizon
,
F.
, 2005, “
Use of Proper Orthogonal Decomposition for Time Interpolation From PIV Data
,”
Exp. Fluids
0723-4864,
39
, pp.
1009
1023
.
24.
Weiland
,
C.
, and
Vlachos
,
P.
, 2007, “
Analysis of the Parallel Blade Vortex Interaction With Leading Edge Blowing Flow Control Using the Proper Orthogonal Decomposition
,”
ASME Fluids Engineering Summer Conference
, San Diego, CA, Paper No. FEDSM2007-37275.
25.
Kurtulus
,
D. F.
,
Scarano
,
F.
, and
David
,
L.
, 2007, “
Unsteady Aerodynamic Forces Estimation on a Square Cylinder by TR-PIV
,”
Exp. Fluids
0723-4864,
42
, pp.
185
196
.
26.
Hinze
,
J. O.
, 1959,
Turbulence
,
McGraw-Hill
,
New York
.
27.
Dano
,
B. P. E.
, and
Liburdy
,
J. A.
, 2006, “
Vortical Structures of a 45° Inclined Pulsed Jet in Crossflow
,”
Fluid Dynamics Conference
, San Francisco, CA, AIAA Paper No. 2006-3543.
28.
Morse
,
D. R.
, and
Liburdy
,
J. A.
, 2007, “
Dynamic Characteristics of Flow Separation from a Low Reynolds Number Wing
,”
Fluids Engineering Conference
, San Diego, CA, Jul. 30–Aug. 2, Paper No. FEDSM20070-37083.
29.
Chen
,
G.
,
Lin
,
Z.
,
Morse
,
D.
,
Snider
,
S.
,
Apte
,
S.
,
Liburdy
,
J.
, and
Zhang
,
E.
, 2008, “
Multiscale Feature Detection in Unsteady Separated Flows
,”
IJNAM
1705-5105,
5
, pp.
17
35
.
30.
Chatterjee
,
A.
, 2000, “
An Introduction to the Proper Orthogonal Decomposition
,”
Curr. Sci.
0011-3891,
78
(
7
), pp.
808
817
.
31.
Sirovich
,
L.
, 1987, “
Turbulence and the Dynamics of Coherent Structures—Part I: Coherent Structures
,”
Q. Appl. Math.
0033-569X,
45
(
3
), pp.
561
571
.
32.
Berkooz
,
G.
,
Holmes
,
P.
, and
Lumley
,
J. L.
, 1993, “
The Proper Orthogonal Decomposition in the Analysis of Turbulent Flows
,”
Annu. Rev. Fluid Mech.
0066-4189,
25
, pp.
539
575
.
33.
Morse
,
D. R.
, and
Liburdy
,
J. A.
, 2008, “
Experimental Time Resolved Flow Features of Separation Over an Elliptic Leading Edge
,”
46th AIAA Aerospace Sciences Meeting and Exhibit
, Reno, NV, Jan. 7–10, AIAA Paper No. 2008-655.