Control of shock-induced boundary layer separation at supersonic speeds

Abstract

The results of a systematic experimental investigation into the effects that Sub- Boundary Layer Vortex Generators (SBVGs) have on reducing normal shock-induced turbulent boundary layer separation are presented. The freestream Mach number and Reynolds number were M. = 1.45 and Re= 15-9xlO6/m, respectively. All measurement instruments and modifications to the wind tunnel were designed and manufactured as part of the project, specifically for these experiments. Boundary layer, wall pressure measurements and flow visualisation were used in the results analysis. The effects of SBVG height, lateral spacing and location upstream of the shock were investigated. A novel, curved shape SBVG was also evaluated and comparisons against the flat vane SBVG were made. The results show that in all but two cases, separation was completely eliminated. As expected, the largest SBVGs with height, h= 55%5, provided the greatest pressure recovery and maximum mixing. However, the shock pressure rise was highest for this case. Reducing the distance to shock to 108 upstream showed an improvement in the flow quality in the interaction region only. The distortion created by the vortices was also found to be closer to the wall in this case. Increasing the spacing of the SBVG pair to n-- 3 provided the greatest improvement in downstream boundary layer flow quality although this resulted in a small separated region at the foot of the shock. In order to achieve an overall improvement in flow quality, it was suggested that a compromise is required between an increase in wave drag and the extent of reduction of boundary layer separation. The effect of curving the SBVGs provided an improved near wall mixing with an improved static and surface total pressure recovery downstream of the separation region. However, an increased viscous drag resulted from these devices.