Effect of tip geometry on blade tip flow and heat transfer

Abstract

In an attempt to increase thrust to weight ratio and efficiency of modern gas turbines, engine designers are always interested in increasing turbine operating temperatures. The benefits are attributed to the fact that higher temperature gases yield a higher energy potential. However, the detrimental effects on the components along the hot gas path can offset the benefits of increasing the operating temperature. The High Pressure Turbine (HPT) first stage blade is one component that is extremely vulnerable to the hot gas. The present study explores the effects of gap height and tip geometry on heat transfer distribution. This investigation differs from those in the past because the tip profile from an in-service High Pressure Turbine of an aircraft engine was used. Other experiments have used the E3 test blade or a power generation blade that have different characteristics. The pressure ratio (inlet total pressure to exit static pressure) used was 1.2 which is lower than the actual pressure ratio this blade sees in service (PR = 1.7). A transient liquid crystal technique was used to obtain the tip heat transfer distributions similar to that used by Azad et al. (2000). Pressure measurements were made on the blade surface and on the shroud for different tip geometries and tip gaps to characterize the leakage flow and understand the heat transfer distributions.