Current Research | Biomimetics

Parametric Study on a Cylinder Drag Reduction Using Downstream Undulating Foil

By Wendi Liu, Dr Qing Xiao

This study is a flow system with a D-sectional cylinder combined with an undulating NACA0012 foil in the wake of cylinder. Cylinder drag force could be considerably reduced if the foil is properly placed in the cylinder wake. In this study, a detailed parametric study on this coupled cylinder-undulating-foil system is carried out by numerical simulation. Particular interest is focused on how Reynolds number, relative size of foil and cylinder, foil undulating frequency, wavelength and gap between cylinder and foil affect the cylinder drag, lift force as well as foil thrust. For a range of flow and geometry parameters studied here, our results show that the maximum cylinder drag and lift coefficient can reduce as 57.4% and 63.3% relative to the cylinder without undulating foil, respectively. Foil thrust coefficient increases to 4 times as compared to single foil. Distinguished from conventional cylinder vortex control method, coupled cylinder-undulating foil system provides some new insights on the vortex control and suppression mechanism.

This numerical study examines the potential of cylinder wake vortex control using a downstream undulating foil. It distinguishes itself considerably from our recent research, which focuses on the propulsion performance enhancement of undulating foil by extracting energy from the upstream cylinder wake. The present investigation covers a much wider range of kinematic and geometric parameters of this coupled cylinder�Cfoil system, such as the foil undulating frequency Stf, wavelength (λf) and the gap ratio (L/c) and cylinder-foil relative size (D/c). It aims for obtaining an optimal parametric range to achieve a significant cylinder drag reduction, which is impossible to be accomplished by our earlier study on the limited parameters. Our results show that the proper placement of foil, with its chord length equal to the upstream cylinder diameter, can result in a suppression of cylinder vortex shedding and an improvement in downstream foil propulsion. The detailed flow field analysis reveals that, such benefit is strongly linked to the interaction between the cylinder wake vortex and the reversed Karman vortex street, which is shedding continuously at the foil leading edge associated with foil undulation locomotion. This new finding undetected by preceding investigations prompts further study in the near future.

Please refer to:

Qing Xiao, Wendi Liu and Jianxin Hu. "Parametric study on a cylinder drag reduction using downstream undulating foil." European Journal of Mechanics-B/Fluids 36 (2012): pp 48-62.

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