This paper presents data showing the three-dimensional vortical structures in the near wake region of circular cylinders. The in-plane velocity field was measured using a digital Particle Image Velocimetry (PIV) technique. The vortical structures are found to include inclined counter-rotating longitudinal vortices in the braids joining consecutive Ka´rma´n vortices. A simple vortex-pair model is proposed to estimate velocity perturbation induced by the longitudinal vortices in the near wake region. The perturbation resulting from the longitudinal vortices is shown to induce spanwise velocity modulation and a velocity spike of a nominally two-dimensional vortex street.

1.
Adrian
R. J.
,
1991
, “
Particle Imaging Techniques for Experimental Fluid Mechanics
,”
Annual Review of Fluid Mechanics
, Vol.
23
, pp.
261
304
.
2.
Barker
D. B.
, and
Fourney
M. E.
,
1977
, “
Measuring Fluid Velocities with Speckle Patterns
,”
Optics Letters
, Vol.
1
, No.
4
, pp.
135
137
.
3.
Bays-Muchmore
B.
, and
Ahmed
A.
,
1993
, “
On Streamwise Vortices in Turbulent Wakes of Cylinders
,”
Physics of Fluids A
, Vol.
5
, No.
2
, pp.
387
392
.
4.
Bernal
L. P.
, and
Roshko
A.
,
1986
, “
Streamwise Vortex Structure in Plane Mixing Layers
,”
Journal of Fluid Mechanics
, Vol.
170
, pp.
499
525
.
5.
Buchhave
P.
,
1992
, “
Particle Image Velocimetry—Status and Trends
,”
Experimental Thermal and Fluid Science
, Vol.
5
, pp.
586
604
.
6.
Ferre
J. A.
,
Mumford
J. C.
,
Savill
A. M.
, and
Ciralt
F.
,
1990
, “
Three-dimensional Large-eddy Motions and Fine-scale Activity in a Plane Wake
,”
Journal of Fluid Mechanics
, Vol.
210
, pp.
371
414
.
7.
Huang
Lein-Saing
, and
Ho
Chih-Ming
,
1990
, “
Small-scale Transition in a Plane Mixing Layer
,”
Journal of Fluid Mechanics
, Vol.
210
, pp.
475
500
.
8.
Hussain
A. K. M. Fazle
,
1986
, “
Coherent Structures and Turbulenc
,”
Journal of Fluid Mechanics
, Vol.
173
, pp.
303
356
.
9.
Meiburg
E.
, and
Lasheras
J. C.
,
1988
, “
Experimental and Numerical Investigation of the Three-dimensional Transition in Plane Wakes
,”
Journal of Fluid Mechanics
, Vol.
190
, pp.
1
37
.
10.
Wei
T.
, and
Smith
C. R.
,
1986
, “
Secondary Vortices in the Wake of Circular Cylinders
,”
Journal of Fluid Mechanics
, Vol.
169
, pp.
513
533
.
11.
Welsh, M. C., Soria, J., Sheridan, J., Wu, J., Hourigan, K., and Hamilton, N., 1992, “Three-dimensional Flows in the Wake of a Circular Cylinder,” Album of Visualization, The Visualization Society of Japan, Vol. 9, pp. 17–18.
12.
Williamson
C. H. K.
,
1988
, “
The Existence of Two Stages in the Transition to Three-dimensionality of a Cylinder Wake
,”
Physics of Fluids
, Vol.
31
, No.
11
, pp.
3165
3168
.
13.
Williamson
C. H. K.
,
Wu
J.
, and
Sheridan
J.
,
1995
, “
Scaling of streamwise vortices in wakes
,”
Physics of Fluids
, Vol.
7
, No. 10, pp.
2307
2309
.
14.
Wu
J.
,
Sheridan
J.
,
Soria
J.
, and
Welsh
M. C.
,
1994
a, “
An Experimental Investigation of Streamwise Vortices in the Wake of A Bluff Body
,”
Journal of Fluids & Structures
, Vol.
8
, pp.
621
635
.
15.
Wu
J.
,
Sheridan
J.
,
Welsh
M. C.
,
Hourigan
K.
, and
Thompson
M.
,
1994
b, “
Longitudinal Vortex Structures In a Cylinder Wake
,”
Physics of Fluids
, Vol.
6
, No.
9
, pp.
2883
2885
.
16.
Wu
J.
,
Sheridan
J.
,
Welsh
M. C.
, and
Hourigan
K.
,
1996
, “
Three-dimensional Vortex Structures in a Cylinder Wake
,”
Journal of Fluid Mechanics
, Vol.
312
, pp.
201
222
.
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