Parametric study on a cylinder drag reduction using downstream undulating foil

The motivation of this paper stems from our recent study [Q. Xiao, K. Sun, H. Liu, J.X. Hu, Computational study on near wake interaction between undulation body and a D-section cylinder, Ocean Eng. 38 (2011) 673-683] which shows that, for a flow system with a D-sectional cylinder combined with an undulating NACA0012 foil in the wake of a cylinder, cylinder drag force could be considerably reduced if the foil is properly placed in the cylinder wake. In this study, a further detailed parametric study on this coupled cylinder-undulating foil system is carried out by a numerical simulation. Particular interest is focused on how Reynolds number, the relative size of the foil to the cylinder, the foil undulating frequency, the wavelength and the gap between the cylinder and the 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 the lift coefficient can be reduced as much as 57.4% and 63.3% as compared to the cylinder without the undulating foil. Foil thrust coefficient increases up to 4 times as compared to a single foil. Distinguishing itself from the conventional cylinder vortex control method, the coupled cylinder-undulating foil system provides new insights on the vortex control and suppression mechanism.