Control of Boundary Layer Separation in Supersonic Flow Using Injection Through Microramps

摘要

This study investigated efficacy of injection through MVGs to reduce separation behind a normal shock in a supersonic flow. Three cases, (A) baseline case-plain wall, (B) three numbers of conventional MVGs, and (C) same MVGs with injection of air through them, were investigated using schlieren images, oil flow images, and wall pressure distribution. Oil flow patterns show that, compared to case A, the conventional MVGs decreased both separation bubble and upstream influence through corner separation. Case C decreased the separation bubble to a large extent and also caused flow all along the tunnel floor in between the separation bubbles. Distributed wall jet injection through multiple MVGs causes a uniform increase of energy in the boundary layer across the span of the test section, suppressing separation to a large extent across the span. Schlieren images show that the case B has an oblique shock at the trailing edge and a growing low momentum region behind the MVGs. Case C, on the other hand, shows weak compression waves at the trailing edge of the MVGs and no growing low momentum regions. Case C had the most stable shock of all the three cases. Pressure data shows that the upstream influence due to the corner separation for case C is similar to case A, while the case B has lesser upstream influence. However, the pressure rise just downstream of shock is highest for case C due to the absence of large separation bubbles. Injection through MVGs is an effective method to suppress boundary layer separation behind normal shocks and to decrease shock oscillations. While corner separation increases by a small amount, advantage to intake flows due to very small centerline separation is high.