Experimental study on the wake control of a square cylinder mounted with dual rigid/flexible splitter plates in the subcritical regime

Abstract

The wake control of a bluff body is vital to the safety of structures in the field of coastal and ocean engineering. The quantitative statistics wake control and flow field in the subcritical regime are relatively unexplored. The purpose of this research is to find an optimum arrangement for the wake control of a square cylinder mounted by dual flexible/rigid splitter plates and uncover the physical mechanisms. The Reynolds number based on the side length of the square cylinder is 4.2×103≤Re≤1.0×104. Splitter plates with two thicknesses were adopted, which represents the flexible and rigid splitters, respectively. The splitter length was considered over the range l/L=1∼2 with an increment of Δl/L=0.25. The force exerting on the bluff body and the instantaneous velocity field were measured by the triaxial load cell and particle image velocimetry techniques. The results indicate the modulation of the flapping splitter as well as the splitting effect of the tip vortices determine the lift suppression and the gap flow and streamlined trailing play a vital role in drag reduction. The maximum drag reduction and lift suppression reach ηmax=58.3% and 90.6%, respectively. The flexible splitter outperforms its rigid counterpart, especially at high Reynolds numbers, which is beneficial for those structures in marine engineering. Given the hydrodynamic characteristics and sensitivity to incoming flow conditions, the optimum arrangement is the flexible splitter configuration with splitter length of l/L=1.25∼1.5.