Experiment study of aerodynamic performance for the suction-side and pressure-side winglet-cavity tips in a turbine blade cascade

Abstract

The influences of suction-side and pressure-side winglet-cavity tips on the flow field and aerodynamic performance of a turbine blade with tip clearance have been investigated in a low-speed cascade wind tunnel. The flow field of the cascade outlet is measured by a calibrated five-hole probe. The oil flow visualizations and static pressure of the endwall provide insight into the endwall flow structure of these blade tips. Compared with the results of flat tips at the ratio of tip clearance to blade height of τ/H=1.0%, the results show that the pressure-side winglet-cavity tip reduces the region and loss of tip leakage flow and enhances the passage vortex. Moreover, the suction-side winglet-cavity tip weakens the tip leakage vortex and passage vortex simultaneously with an 11.4% reduction of total pressure losses and a more uniform flow angle than the flat tip. Thus, the suction-side winglet-cavity tip provides better aerodynamic performance. The pressure-side winglet-cavity tip, with a smaller distance between the tip leakage separation line and the suction side in the flow passage, tends to obtain a smaller tip leakage loss, as shown in the endwall oil flow visualization. The reduction of the range of the buffer zone indicates that the interaction between the tip leakage flow and passage flow decreases and the loss of passage vortex increases. A portion of the fluid in the passage enters the cavity from the front of the suction side. These factors weaken the loss of the passage vortex. Although the suction-side winglet-cavity tip shows a larger distance between the tip leakage separation line and the suction side, the reduction of range along the blade height decreases the loss of tip leakage flow. The effects of tip clearance on the aerodynamic performance indicate that the ratio of change in losses to tip clearance for the pressure side winglet-cavity tip is almost equal to the results for the flat tip owing to the change in the losses of tip leakage vortex and passage vortex with various tip clearances. With a 23.4% reduction in the ratio of change in losses to tip clearance, the influences of tip clearance on the outlet flow field of the suction side winglet-cavity tip are smaller than with other blade tip geometries. Overall, the winglet-cavity tip can be used to reduce the loss of tip leakage flow, while the suction side winglet-cavity tip achieves a better aerodynamic performance among the tested winglet cavity tips.