Wake flow pattern modified by small control cylinders at low Reynolds number

• Published in: Journal of fluids and structures Vol. 23; no. 6; pp. 938 - 956
• Main Authors: Kuo, C.-H., Chiou, L.-C., Chen, C.-C.
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01.08.2007; Elsevier
• Subjects: Boundary layer and shear turbulence; Circular cylinder; Computational fluid dynamics; Cylinders; Delay; Drag; Drag reduction; Exact sciences and technology; Fluid dynamics; Fluid flow; Fundamental areas of phenomenology (including applications); General theory; Passive wake control; Physics; Reynolds number; Rotational flow and vorticity; Streams; Turbulent flows, convection, and heat transfer; Unsteady lift; Vortex street; Wakes; Circular cylinder; Unsteady lift; Drag reduction; Passive wake control; Vortex street; Forming processes; Flow separation; Reynolds number; Momentum; Symmetry groups; Passive system; Low Reynolds number; Internal flow; Near wake; Drag; Modelling; Turbulence structure
• ISSN: 0889-9746; 1095-8622
• DOI: 10.1016/j.jfluidstructs.2007.01.002

Passive wake control behind a circular cylinder in uniform flow is studied by numerical simulation for Re D ranging from 80 to 300. Two small control cylinders, with diameter d/D=1/8, are placed at x/D=0.5 and y/D=±0.6. Unlike the 1990 results of Strykowski and Sreenivasan, in the present study, the vortex street behind the main cylinder still exists but the fluctuating lift and the form drag on the main cylinder reduces significantly and monotonously as the Reynolds number increases from 80 to 300. Obstruction of the control cylinders to the incoming flow deflects part of the fluid to pass through the gap between the main and control cylinders, forming two symmetric streams. These streams not only eliminate the flow separation along the rear surface of the main cylinder, they also merge toward the wake centerline to create an advancing momentum in the immediate near-wake region. These two effects significantly reduce the wake width behind the main cylinder and lead to monotonous decrease of the form drag as the Reynolds number increases. As the Reynolds number gets higher, a large amount of the downstream advancing momentum significantly delays the vortex formation farther downstream, leading to a more symmetric flow structure in the near-wake region of the main cylinder. As the Reynolds number increases from 80 to 300, both increasing symmetry of the flow structure in the near-wake and significant delay of the vortex formation are the main reasons for the fluctuating lift to decrease monotonously.