Abstract
The flow around hemispherical bodies was investigated by undertaking wind tunnel measurements using a range of hemisphere and hemisphere-cylinder models immersed in three different turbulent boundary layers. The effects, both on the model surface pressures and on the near wake flow regime, of changes in model geometry and upstream conditions was assessed, whilst the pressure distributions were examined further in order to determine their dependency on Reynolds number and surface roughness. It was found that the critical Reynolds number could be reduced by applying sufficient surface roughness, thus producing a simulation of high Reynolds number flow at lower Reynolds numbers similar to those developed by previous workers on cylinders and spheres in uniform flow. The near wake mean flow patterns and turbulence distributions were ascertained from comprehensive pulsed-wire anemometer measurements, supplemented by visual observations using models in a water channel. The results showed that the shear layer separating from the models comprised strong vorticity, curved such that the lateral component dominated on the wake centre-line whilst the vertical component was the greatest near the ground plane. In addition, the thickness and rate of growth of the shear layer were strongly related to the upstream boundary conditions as were the size of the mean recirculation region and the volume of recirculating fluid. Furthermore, the longitudinal vorticity component was comparatively weak and the main feature of the distributions was a pair of contrarotating vortices - one associated with the shear layer and the other originating upstream of the model in the horseshoe vortex. Two new devices were developed for use in wind tunnel investigations. These were a pressure probe incorporating a light emitting diode, for visualising bluff body wakes, and a heated element probe for locating separation and reattachment points.