Experimental Study on Hydrodynamic Vicous Force Acting on Oscillating Bluff Body

Abstract

The viscous forces acting on various oscillating bluff cylinders are measured by using a forced oscillation mechanism in order to clarify the influences of Reynolds number, KC number, the cross sectional aspect-ratio and the round edge on the drag and the added-mass coefficients. From the experimental results, it is found that the characteristics of the drag coefficients of rectangular cylinders with small sectional aspect-ratio at low KC number (KC<4) vary significantly with a slight change of the sectional aspect-ratio. The flow visualization results indicate that the change of the drag coefficients is highly related to the existence of the reattachment of the front-edge separation flow at the body side. The effect of the round edge on the drag is greater for the shape like a square than for the cylinder with small sectional aspect-ratio like a flat plate. In the region of KC number under 6, the added-mass coefficients of rectangular cylinders increase with KC number due to the created vorticies, while their values at KC number above 6 become different depending on their sectional aspect-ratios. For round-edge cylinders the added-mass coefficients are almost constant at KC number under 6, and have the same tendency as the rectangular cylinders at KC number above 6.