Investigation of upstream wake effect on the endwall flow of a highly loaded compressor cascade at low Reynolds number

Abstract

Compressor flow loss is largely contributed by the blade endwall flow deterioration, especially for advanced jet engines operating at high altitudes and low Reynolds number (Re) conditions. To reduce the significant losses in the compressor blade endwall regions under low Re, this paper numerically investigates the potential control effect of the inherent upstream wakes - manifesting themselves as periodic flow disturbances within the downstream blade passage - on the aerodynamic performance of a highly loaded compressor cascade at a low Re condition induced via low-speed inflow, and particular emphasis is placed on the upstream wake effect on the endwall flow separation and mechanism. Firstly, the impact of Re on compressor cascade performance is clarified; Then, the optimal upstream wake parameters of sweep frequency (f) and flow coefficient (Ø) are developed at a relative low Re condition, where a 20.1% reduction in compressor cascade total pressure loss is achieved. Subsequently, the underlying flow mechanism of upstream wake effect on the compressor cascade performance improvement are explored in depth from the perspectives of vortex, separation and secondary flow, where the positive radial vorticity and streamwise vorticity of upstream wakes are proved to play critical roles on the suppression of suction surface laminar separation bubble and endwall, respectively. Furthermore, typical flow structure models of the highly loaded compressor cascade at low Re are developed based on the detailed flow mechanism investigation. All the analyses provide theoretical references for the design of advanced jet engines operating at high altitudes and low Re.