Hydrodynamic characteristics and wake structure of flow over a round-ended cylinder at a low Reynolds number

Abstract

Hydrodynamic characteristics and wake structures of the flow over a round-ended cylinder are invaluable for the design of associated cylindrical structures such as bridge piers and submerged floating tunnels. This paper reports the results of a numerical investigation into the flow past a round-ended cylinder and the associated hydrodynamic forces as well as the evolution of vortex structure and boundary layer separation. The effect of incidence angle α, ranging from 0° to 90°, is examined at a low Reynolds number of 100 based on the projected length. Both the drag and lift forces are sensitive to the incidence angle. When 0° < α < 90°, boundary layers asymmetrically separate from two sides of the cylinder, giving rise to a time-mean pressure difference that is not perpendicular to the incoming flow direction. There are two directly related results, one is the non-zero time-mean lift coefficient, and the other is the occurrence of a secondary frequency of drag coefficient, the same as that of lift coefficient. The most forward separation point of the upper boundary layer and the maximum size difference of vortices generated from two sides contribute to the maximum time-mean lift coefficient occurring at α = 45°. The vortex formation length is shortened with increasing α, resulting in the augment of the fluctuation amplitudes of fluid forces. The enlargement of drag force is mainly attributed to the broadened wake width with the increase in α.