This investigation examines the flow produced by a tandem cylinder system with the downstream cylinder yawed to the mean flow direction. The yaw angle was varied from $α=90deg$ (two parallel tandem cylinders) to $α=60deg$; this has the effect of varying the local spacing ratio between the cylinders. Fluctuating pressure and hot-wire measurements were used to determine the vortex-shedding frequencies and flow regimes produced by this previously uninvestigated flow. The results showed that the frequency and magnitude of the vortex shedding varies along the cylinder span depending on the local spacing ratio between the cylinders. In all cases the vortex-shedding frequency observed on the front cylinder had the same shedding frequency as the rear cylinder. In general, at small local spacing ratios the cylinders behaved as a single large body with the shear layers separating from the upstream cylinder and attaching on the downstream cylinder, this caused a correspondingly large, low frequency wake. At other positions where the local span of the tandem cylinder system was larger, small-scale vortices began to form in the gap between the cylinders, which in turn increased the vortex-shedding frequency. At the largest spacings, classical vortex shedding persisted in the gap formed between the cylinders, and both cylinders shed vortices as separate bodies with shedding frequencies typical of single cylinders. At certain local spacing ratios two distinct vortex-shedding frequencies occurred indicating that there was some overlap in these flow regimes.

## References

1.
Khorrami
,
M. R.
,
Choudhari
,
M. M.
,
Lockard
,
D. P.
,
Jenkins
,
L. N.
, and
McGinley
,
C. B.
,
2007
, “
Unsteady Flowfield Around Tandem Cylinders as Prototype Component Interaction in Airframe Noise
,”
AIAA J.
,
45
(
8
), pp.
1930
1941
.10.2514/1.23690
2.
Fitzpatrick
,
J.
,
2003
, “
Flow/Acoustic Interactions of Two Cylinders in Cross-Flow
,”
J. Fluids Struct.
,
17
, pp.
97
113
.10.1016/S0889-9746(02)00091-9
3.
Ramberg
,
S.
,
1983
, “
The Effects of Yaw Angle and Finite Length Upon the Vortex Wakes of Stationary and Vibrating Circular Cylinders
,”
J. Fluid Mech.
,
128
, pp.
81
107
.10.1017/S0022112083000397
4.
Snarski
,
S. R.
,
2003
, “
Flow Over Yawed Circular Cylinders: Wall Pressure Spectra and Flow Regimes
,”
Phys. Fluids
,
16
, pp.
344
359
.10.1063/1.1627764
5.
Marshall
,
J.
,
2003
, “
Wake Dynamics of a Yawed Cylinder
,”
ASME J. Fluids Eng.
,
125
, pp.
97
103
.10.1115/1.1523069
6.
Hogan
,
J. D.
, and
Hall
,
J. W.
,
2010
, “
The Spanwise Dependence of Vortex-Shedding From Yawed Circular Cylinders
,”
ASME J. Pressure Vessel Technol.
,
132
, p.
031301
.10.1115/1.4000732
7.
Hori
,
E.
,
1959
, “
Experiments on Flow Around a Pair of Parallel Circular Cylinders
,”
Proceedings of the 9th Japan National Congress for Applied Mechanics
, pp.
231
234
.
8.
Arie
,
M.
,
Kiya
,
M.
,
Moriya
,
M.
, and
Mori
,
H.
,
1983
, “
Pressure Fluctuations on the Surface of Two Circular Cylinders in Tandem Arrangement
,”
ASME J. Fluids Eng.
,
105
, pp.
161
167
.10.1115/1.3240956
9.
Zdravkovich
,
M. M.
,
1977
, “
Review of Flow Interference Between Two Circular Cylinders in Various Arrangements
,”
ASME J. Fluids Eng.
,
99
, pp.
618
633
.10.1115/1.3448871
10.
Zdravkovich
,
M. M.
,
1987
, “
The Effects of Interference Between Circular Cylinders in Cross Flow
,”
J. Fluids Struct.
,
1
, pp.
239
261
.10.1016/S0889-9746(87)90355-0
11.
Zdravkovich
,
M.
,
2003
,
Flow Around Circular Cylinders, Vol 2: Applications
.
Oxford Science
,
Oxford
.
12.
Hall
,
J. W.
,
,
S.
, and
Weaver
,
D.
,
2003
, “
Vortex-Shedding From Single and Tandem Cylinders in the Presence of Applied Sound
,”
J. Fluids Struct.
,
18
, pp.
741
758
.10.1016/j.jfluidstructs.2003.06.003
13.
Mohany
,
A.
, and
,
S.
,
2005
, “
Flow-Excited Acoustic Resonance of Two Tandem Cylinders in Cross-Flow
,”
J. Fluids Struct.
,
21
(
1
), pp. 103–119.10.1016/j.jfluidstructs.2005.05.018
14.
Xu
,
G.
, and
Zhou
,
Y.
,
2004
, “
Strouhal Numbers in the Wake of Two Inline Cylinders
,”
Exp. Fluids
,
37
(
2
), pp.
248
256
.10.1007/s00348-004-0808-0
15.
Igarashi
,
T.
,
1981
, “
Characteristics of the Flow Around Two Circular Cylinders Arranged in Tandem: 1st Report
,”
Bull. JSME
,
24
(
188
), pp.
323
331
.10.1299/jsme1958.24.323
16.
Igarashi
,
T.
,
1984
, “
Characteristics of the Flow Around Two Circular Cylinders Arranged in Tandem: 2nd Report, Unique Phenomenon at Small Spacing
,”
Bull. JSME
,
27
(
233
), pp.
2380
2387
.10.1299/jsme1958.27.2380
17.
Ljungkrona
,
L.
,
Norberg
,
C.
, and
Sunden
,
B.
,
1991
, “
Free-Stream Turbulence and Tube Spacing Effects on Surface Pressure Fluctuations for Two Tubes in an In-Line Arrangement
,”
J. Fluids Struct.
,
5
, pp.
701
727
.10.1016/0889-9746(91)90364-U
18.
Ljungkrona
,
L.
, and
Sunden
,
B.
,
1993
, “
Flow Visualization and Surface Pressure Measurement on Two Tubes in an Inline Arrangement
,”
Exp. Thermal Fluid Sci.
,
6
, pp.
15
27
.10.1016/0894-1777(93)90037-J
19.
Okajima
,
A.
,
1979
, “
Flows Around Two Tandem Circular Cylinders at Very High Reynolds Numbers
,”
Bull. JSME
,
22
, pp.
504
511
.10.1299/jsme1958.22.504
20.
Wu
,
J.
,
Welch
,
L.
,
Welsh
,
M.
,
Sheridan
,
J.
, and
Walker
,
G.
,
1994
, “
Spanwise Wake Structures of a Circular Cylinder and Two Circular Cylinders in Tandem
,”
Exp. Thermal Fluid Sci.
,
9
, pp.
299
308
.10.1016/0894-1777(94)90032-9
21.
Lam
,
K.
,
Lin
,
Y.
,
Zou
,
L.
, and
Liu
,
Y.
,
2012
, “
Numerical Simulation of Flows Around Two Unyawed and Yawed Wavy Cylinders in Tandem Arrangement
,”
J. Fluids Struct.
,
28
, pp.
135
151
.10.1016/j.jfluidstructs.2011.08.012
22.
Sumner
,
D.
,
2010
, “
Two Circular Cylinders in Cross-Flow: A Review
,”
J. Fluids Struct.
,
26
, pp.
849
899
.10.1016/j.jfluidstructs.2010.07.001
23.
Hogan
,
J. D.
, and
Hall
,
J. W.
,
2011
, “Experimental Study of Pressure Fluctuations from Yawed Circular Cylinders,”
AIAA J.
,
49
(
11
), pp. 2349–2356.
24.
Gerrard
,
J.
,
1955
, “
Measurements of the Sound From Circular Cylinders in an Airstream
,”
Proc. Phys. Soc.
,
7
, pp.
453
461
.