Three dimensional shock induced separated flow

Abstract

Supersonic flow over 3-dimensional bodies protruding out of the turbulent boundary layer was investigated by performing experiments and numerical computations. A parametric study was undertaken varying shapes, heights, and diameters of the protuberance. To study the Mach number effects on the shock boundary layer interactions due to protuberances flows with varying Mach numbers (1.5, 2, 2.5, 3, 3.5) were also examined. Surface oil flow technique, surface pressure measurements and schlieren flow visualization using a high-speed camera were employed along with 3-dimensional RANS computations to elicit flow features such as core of the horseshoe vortex, which greatly influences the flow in recirculation bubble. Though some of the parameters involved in such interactions are individually investigated in the literature, a comprehensive study is still lacking. It was observed that the viscous interaction was strongly related to the inviscid phenomenon happening close to the surface of the protuberance. Radius of curvature of the inviscid shock at the nose was found to be a determining parameter incorporating information on adverse pressure gradient experienced by local boundary layer, geometrical parameters of the protuberances, and Mach number of the incoming flow. Based on this, a scaling law is presented to relate the separation length involved in such interaction with various geometrical and incoming flow parameters. The scaled separation length was predicted remarkably well by the proposed correlation. As a comprehensive correlation, it was also tested with data from a 2-dimensional forward facing step study in the literature, and a good agreement was found. It was also observed that the location of the horseshoe vortex core was also dependent on the inviscid shock in the same way as is separation length.