Velocity shear flow over rectangular cylinders with different side ratios

Abstract

Large Eddy Simulation (LES) is carried out to investigate the velocity shear flow over rectangular cylinders with different side ratios of B/D=1, 5 and 8 (B: breadth of the cylinder, D: depth of the cylinder). The shear rate is expressed by a dimensionless shear parameter, defined by the oncoming velocity gradient, the cylinder thickness and the upstream velocity at the center plane of the cylinder. The Reynolds number based on the cylinder depth and the upstream velocity at the center plane of the cylinder is 22,000. Particular attention is devoted to variations with side ratio of shear flow and aerodynamic forces acting on the rectangular cylinders. It is shown that the side-ratio-dependent Strouhal number remains almost unchanged with shear parameter. The shear flow patterns around the rectangular cylinders vary with side ratio, resulting in a side-ratio-dependent aerodynamic force. An interesting finding is that the lift forces on the rectangular cylinders with B/D=5 and 8 act from the high-velocity side to the low-velocity side, while for B/D=1 they act from the low-velocity side to the high-velocity side. The stagnation point moves to the high-velocity side almost linearly with shear parameter for all investigated side ratios, implying that the movement of stagnation point to the high-velocity side is an inherent behavior in shear flow. In addition, the unsteady flow structures and the mechanism for the change of aerodynamic force with side ratio in shear flows are investigated.