Experimental study of endwall flow in a low-speed linear compressor cascade: effect of over-tip leakage

This paper describes the study of endwall flow modification due to over-tip leakage flow in axial compressor blades. Un-shrouded axial compressor stator and rotor blades in aero-engines and land based gas turbines are subjected to over-tip leakage flow to allow for the relative motion between the unsupported end of the aerofoil and the near endwall surface that moves relative to it. The leakage flow that results is unturned by the blade and this causes non-uniform flow downstream of the blade-row that mixes out to produce a total pressure loss. The leakage flow also causes the formation of a ‘leakage-vortex’ which causes further losses within and downstream of the blade-row through its own viscous mixing with the fluid around it. In many compressors the blockage created by these effects is known to dictate the point of stall inception and hence the stability of the compressor and its useful operating range. In this paper an experimental study into the effects of the leakage flow, namely, the formation of the leakage vortex and the generation of the losses under a low Reynolds number condition is discussed. It has been shown that the endwall flow is signifi-cantly altered by the presence of the leakage vortex as it weakens the classical secondary flow.