The Effect of Gap Size and Reynolds Number on Turbine Blade Flat and Suction-Side Squealer Tip Flowfields

In order to further the understanding of turbine tip leakage and passage flow mechanisms for undesirable entropy production, an experiment was conducted in a linear cascade at the Hessert Laboratory. Blade surface and tip endwall static pressure, total pressure loss, and wake vorticity measurements were taken to document the effects of upstream axial Reynolds number, 100000 < Re₂ < 500000, and tip gap height, 0.015 < g/c_x < 0.05 for flat and partial, suction-side squealer tip geometries. Interaction of tip leakage and passage vortices proved critical, and an inverse relationship was observed between the two structures in terms of streamwise vorticity, core total pressure loss, and the vortex size denoted by the -Ì_åÈ₂ criterion. Highlighting a considerable limitation of the passive control strategy, the squealer tip more effectively reduced total pressure loss under a 'thick' blade model, defined by a blade thickness to gap height ratio, t/g = 3.5, than at a slightly larger clearance.