Curvature-Driven Favorable Pressure Gradient Effects on Shock Boundary Layer Interactions

Abstract

Efficient high-speed air breathing propulsion is a key enabling technology for robust long distance hypersonic flight. However, the physics that drive the design of these propulsion systems was extremely complex with a wide range of aerodynamic and chemistry scales, complex multi-phase interactions, and high sensitivity to vehicle trajectory. In a scramjet engine, shockwaves generated from the inlet cowl lip typically interact with a growing boundary layer along the internal surface of the isolator. The resulting shock boundary layer interaction (SBLI) can induce flow separation and oscillatory disturbances that reduce combustion efficiency. Furthermore, these complex interactions can lead to unstart of a scramjet engine. The objective of the current study was to utilize computational fluid dynamics (CFD) of a high Reynolds number flow at Mach 2.2 to study the effect that a curvature driven favorable pressure gradient (FPG) had on a SBLI separation size. It was found that through slight wall curvature, an FPG significantly reduced the separation region of an SBLI. For the 12-degree wedge, compared to the zero pressure gradient (ZPG) case, the separation size reduction was 30.7% and 64.8% for the weak pressure gradient (WPG) and strong pressure gradient (SPG) respectively. Experimentally, through particle image velocimetry (PIV), similar results were found. The 14-degree wedge shockwave impingement on the WPG achieved a separation size reduction of 54.4% compared to the ZPG. The 16-degree wedge shockwave impingement on the SPG achieved a separation size reduction of 74.2% compared to the ZPG. These findings showed that slight wall curvature could be used for reduction of a shockwave induced separation in a high-speed inlet. Implementation of these findings could increase the operational range of scramjet engines and allow for more robust high-speed flight.