Aerothermal Performance of Axially Varying Winglet-Squealer Blade Tips

Abstract

High-pressure turbine blades are usually susceptible to secondary flow losses due to fluid flow between the casing and the blade tip. In this study, we have evaluated the performance of several blade tip designs for different combinations of winglets and squealer geometries toward mitigating tip leakage losses. The effects of considering relative casing motion (RCM) on the aerothermal performance are also brought out. In particular, we have considered three different blade tip designs, which include winglets, top winglet bottom squealer (TWBS), and top squealer bottom winglet (TSBW). Inspired by the partial winglet configurations studied in the literature, we have also examined designs with partial squealers and winglets. The performance of all the designs and the dynamics within the tip gap is discussed through the distributions of total pressure loss within the tip gap and Nusselt number over the blade tips. Of all the blade tip designs, the aerothermal performance of a 100% TWBS design is demonstrated to be superior, both with and without relative casing motion. When compared to a flat tip design, a 100% TWBS design showed a 15% reduction in total pressure loss and a 22% reduction in the average Nusselt number over the blade tip. For this design, accounting for the relative casing motion showed a marked reduction in the total pressure loss and the heat transferred to the blade tip. In particular, RCM is shown to suppress the “hot spot” associated with a cavity vortex within the squealer cavity.