| The internal flow field in an abrupt entrance supersonic diffuser has been investigated by use of pitot and wall static pressure measurements, Schlieren photography and an invisicid method of characteristics (MOC) code. The model used was a constant area duct with rectangular cross-section fed by a sonic orifice. Pressure measurements show good agreement with the MOC results which indicate a significant loss in total pressure resulting from the strong shocks generated by the area change. Mach number and pressure oscillations are attenuated by the fourth shock reflection. Boundary layer growth is more rapid than in diffusers with smooth entrances owing to the shock-boundary layer interactions. Measured wall pressures are about double the isentropic expansion values. The turbulent boundary layer separates and reattaches at the first and second shock reflection as a result of the pressure increase. Recovery of pressure and subsonic flow is similar to constant area diffusers with smooth entrance conditions, but slightly less efficient. Pressure recovery begins at a wall pressure of about 1/5 the ambient pressure in short diffusers operating below ambient. Schlieren photographs provide a visual description of the flow field as well as quantitative details for use in analysis of the shock effects. The results of this study are applicable to solid rocket motor thrust reverser ports and laser screen nozzles and other similar geometries. |
