Interference drag and flow structure around cylinder-sphere junction

Abstract

Wind tunnel experiments and numerical simulations have been conducted on composite bodies consisting of a sphere connected atop a cylinder as well as the individual component shapes. Drag forces were measured in order to determine the interference drag caused by the junction between the two shapes at varying diameter ratios and Reynolds numbers. Increasing the sphere/cylinder diameter ratio was found to increase the interference drag. A dimensional analysis of these results allows the data to collapse to a single trend line useful for calculating interference drag or, in combination with historical sphere and cylinder data, total drag on such composite shapes. Simulation results reveal that the drag on the sphere component of the composite body increases substantially in comparison to the drag on an individual sphere, largely due to decreases in the pressure on the downstream side. For the composite body, in comparison to the individual shapes, an increasing sphere diameter results in wake modifications including increased vorticity, turbulence intensity and regions of low velocity downstream of the cylinder/sphere junction.