Tip leakage vortex and its breakdown mechanism in aspirated compressor cascades designed with conventional method and curvature induced pressure recovery concept

Boundary layer suction (BLS), or aspiration, is an effective methodology to eliminate flow separation and improve blade loading in axial compressors. The objective of this study is to reveal the flow physics and loss mechanism of tip leakage vortex in aspirated compressor cascades with multiple loading levels under diffusion factor ranging from 0.42 to 0.71. The effect of blade pressure distribution on tip leakage flows was investigated numerically based on three aspirated blades, including the one designed with conventional method and the other two designed with curvature induced pressure recovery. The influences of tip clearance dimension and BLS schemes (BLS location, BLS height and BLS mass flow rate) on tip leakage vortex as well as its breakdown mechanism were investigated. Results show that a pseudo-shock was found in aspirated compressor cascades designed with conventional method and curvature induce pressure recovery concept. Compared with conventional compressor blades, the main flow phenomenon of tip leakage flow of aspirated compressor blades is the tip leakage vortex breakdown (TLVB) caused by strong adverse pressure gradient introduced by BLS. The TLVB phenomenon occurred both in conventionally loaded compressor cascade and highly loaded compressor cascade. For conventionally loaded blade, TLVB phenomenon occurred under low tip clearance condition but disappeared under high tip clearance condition due to increased strength of tip leakage vortex. Lower BLS mass flow resulted in weaker pseudo-shock, which reduced the swirl number of tip leakage vortex and improved the vortex breakdown phenomenon as a consequence. The vortex breakdown of highly loaded cascades was resulted from the joint action of high blade loading and pseudo-shock. Pseudo-shock designed near blade trailing edge resulted in higher leakage mass flow but promised superior tip leakage flow field. For all the aspirated cascades studied, the tip leakage loss decreased as tip clearance dimension increased, which was opposite to the results of conventional compressor cascade.