Investigation of separate flow around a prolate spheroid in laminar and turbulent flow by an improved oil-flow visualization technique

Structures of the skin friction lines (SFL) appearing on a prolate spheroid in laminar and turbulent flows were investigated and compared by using an improved oil-flow visualization technique. Different topological structures of SFL were observed in laminar and turbulent flows. At 30° and 20° incidences, there are three separation lines on each side beside the symmetry plane when the flow is laminar and Re=1.4×10⁶. In turbulent flow, two separation lines with positions shifted downstream were observed in experiments under the same conditions. Meanwhile, the secondary separation line is shortened. The effects of small grains set on the surface of prolate spheroid on SFL were also observed arid analyzed. In laminar flow, Re=1.4×10⁶, the shape of separation line is affected prominently by the nearby grains. However by decreasing Reynolds number to 0.9×10⁶, the influence of grains becomes slight. The effects observed in our experiments occur only at places adjacent to the wall and are interpreted in this paper by vortices interaction.