The hemisphere-cylinder at an angle of attack

Abstract

An experimental investigation was carried out of the flow over a hemisphere-cylinder at angles of attack (α = 0° to 90°, Visualizations of skin-friction lines were conducted and were focused mainly on the development of the laminar separation bubble as a function of angle of attack, the conditions under which open and closed separation exist and the interaction between the separation bubble and the leeward vortices. A digital processing method was developed to convert flow visualizations to numerical data. Static pressure measurements over a large range of Reynolds numbers were obtained for two models with different sizes and the same length-to-diameter ratios. Detailed velocity fields, mapped out by a seven hole probe and a laser-Doppler velocimeter (LDV) probe, were carefully examined to provide information on the development of vortical structures on the surface of the model. Comparisons were made of the results obtained using these two instruments. The flowfield in the wake of the hemispherecylinder was also examined at an angle of attack α = 30°. A small bead was strategically placed near the nose to force vortex asymmetry. Difference sizes of bead were also tested to investigate the effectiveness on the asymmetric pattern. Hot-wire anemometers and a dynamic signal analyzer were employed to study the unsteady motion of leeward vortices.