Abstract

Experimental and numerical methods were used to investigate the aerodynamic effects of a near-casing streamwise incoming vortex flow on the tip leakage flow of different tip geometries in an unshrouded high pressure turbine. A flat tip, a cavity tip and a suction-side winglet tip were investigated with quasi-steady method first. A swirl generator was used to produce the incoming vortex in a linear cascade. In the flat tip case, the incoming vortex interacts with the tip leakage flow and the two vortices gradually mix together. The tip leakage loss is reduced due to the streamwise momentum supplement within the tip leakage vortex core. For the cavity tip, the tip leakage vortex appears at a location relatively downstream in the blade passage compared to the flat tip and no evident vortex interaction is observed. The incoming vortex causes extra viscous dissipation within the blade passage and increases the aerodynamic loss for the cavity tip. For the winglet tip, the extension of the suction side winglet tends to push the incoming vortex and the tip leakage vortex move and mix together, thus reducing the loss. Then the effects of periodic unsteady vortex transportations were investigated by conducting unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations. The incoming vortex is stretched as it transports downstream. The unsteady incoming vortex is easier to interact with the tip leakage vortex for the winglet tip. As a result, the winglet tip is the most efficient tip design with unsteady incoming flow among the three tips, and achieves 3.7% reduction of mixed-out loss coefficient compared to the flat tip, larger than 2.8% reduction in the uniform inlet condition. The detailed loss mechanism is discussed in the paper.

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