An Experimental study for flow characteristics of a Square Cylinder with Moving Ground System

The objective of present study is comparing the moving ground and fixed ground on the flow characteristics of a square cylinder. It is investigated the influence of the gap height and ground conditions on the vortex formation as well as the dynamic behavior of the wake flow around the square cylinder near a ground. The experiments were carried out in an open circuit low turbulence subsonic wind tunnel at the Institute of Fluid Science in Tohoku University. The wind tunnel is equipped by moving belt system to simulate the ground effect. The average inflow velocity was set to be u∞=10m/s, Re=20,000 (based on the on-coming velocity, u∞, and the cylinder height, D). The inflow velocity was measured by Pitot-static tube mounted in test section. The mean velocity and the turbulent field around a square cylinder were measured using a twocomponent Particle Image Velocimetry (PIV, hereafter). A hot-wire Anemometry (HWA, hereafter) was used to capture the shedding frequency though a continuous signal of velocity fluctuation. For flow visualization, a laser light-sheet visualization technique with a smoke-tracer was employed to observe the dynamic behavior of the flow. From these results, Strouhal number can be found, where the transition region of the Strouhal number is at G/D=0.5~0.7 above the critical gap height. And as the boundary layer on the ground increases, the critical gap height increases due to the interference from the ground. It is also observed that the position (y/G) and the magnitude of maximum average velocity (u/u∞) in the gap region affect the regular vortex shedding as the gap height increases.