Supersonic Compressor Cascades—An Analysis of the Entrance Region Flow Field Containing Detached Shock Waves

Abstract

When the incoming air flow to a supersonic compressor rotor or cascade has a subsonic axial velocity component, a system of shock and Mach waves originates in the blade leading-edge region, propagates upstream of successive blades, and alters the incident flow conditions. The continuity constraint establishes a unique relationship between the incident Mach number and air flow angle. The shocks are detached and curved with blunt leading edged blades thereby violating the assumptions inherent in the classical simple wave analysis of this flow induction process. The current work employs detached shock models and a rotational flow analysis by the method of characteristics to investigate the effects of airfoil leading edge radius and cascade solidity on the unique incidence values and entrance region total pressure losses. The calculated results are compared to simple wave theory for the entrance region and it is shown that the simple wave assumptions lead to appreciable errors when detached shocks are present in the flow field.