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Journal of Flow Visualization and Image Processing
SJR: 0.11 SNIP: 0.312 CiteScore™: 0.1

ISSN Print: 1065-3090
ISSN Online: 1940-4336

Journal of Flow Visualization and Image Processing

DOI: 10.1615/JFlowVisImageProc.v9.i2-3.30
16 pages


Zhiwen WANG
Cognitive Science Department of Xiamen University
Yu Zhou
Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong; Institute for Turbulence-Noise-Vibration Interaction and Control Shenzhen Graduate School, Harbin Institute of Technology Shenzhen, 518055, China
Hui Li
Department of Mechanical Engineering, Kagoshima University, Korimoto, Kagoshima, Japan


The near-wake of two side-by-side circular cylinders was studied using the laser-illuminated flow-visualization technique. Three T/d values, i.e., 3.00, 1.70, and 1.13, were investigated, where T is the centre-to-centre cylinder spacing and d is the cylinder diameter; they represent three typical flow regimes. The vortex formation, topology and downstream evolution are discussed in detail. At T/d = 3.00, two vortex streets are observed behind the cylinders. The two streets are predominantly symmetrical about the flow centreline. As T/d reduces to 1.70, the gap flow between the cylinders is deflected, forming one narrow and one wide wake behind the cylinders. The deflected gap flow is bi-stable, as previously reported. One interesting observation was made, that is, an exceptionally large gap vortex occurred and subsequently triggered the changeover of the gap flow deflection from one side to another. A new explanation is therefore proposed for the bi-stable gap flow deflection. At T/d = 1.13, the two cylinders acted like a single bluff body, resulting in one single Karman vortex street. Nevertheless, they are different from a single structure. The gap bleeding is unequivocally identifiable and could play a role in determining the vortex pattern. The bleeding is mostly biased towards one cylinder. This is associated with vortices shed alternately from the outer side of the two cylinders. On the other hand, the symmetric vortex shedding occurs when the bleeding was unbiased.