Aspect ratio and end wall effects on the surface pressure coefficient of a circular cylinder

Abstract

The effects of end wall conditions and aspect ratios on the surface pressure and the local drag coefficients of a circular cylinder were examined experimentally at a blockage ratio of 3.0% and a Reynolds number of 8000. Both end walls supporting the cylinder were flat plates with different tip conditions on which transitional boundary layers were formed. The ratio of the boundary layer thickness to cylinder diameter at the cylinder position was 0.60 and 0.83, and the aspect ratio was varied from 8 to 32. Regarding the thick wall boundary layer, the base pressure coefficient along the cylinder axis was mostly constant for all aspect ratios, with the exclusion of the end wall vicinity, but rapidly rose as the aspect ratio decreased. In the case of the thin wall boundary layer, the base pressure coefficient was very little constant along the cylinder axis, but the difference for various aspect ratios was relatively small. The local pressure drag coefficient at the mid-span increased in the case of the high aspect ratio and the thin boundary layer.