Computational Study of the Thermal Performance of an Unshrouded High Pressure Turbine Blade Tip

The tip leakage flow imposes large thermal loads on unshrouded high pressure turbine blades. Obtaining a good thermal performance of the blade tip represents a major challenge for the turbine designer. In this paper, numerical methods have been employed to study the thermal performance of a flat tip and a cavity tip at five tip gaps of 0.4%, 1%, 1.6% 2.2% and 2.8% of the chord. For the flat tip, the tip leakage flow separates from the sharp pressure side edge then reattaches on the blade tip. The reattachment region suffers from a high heat transfer coefficient. As the size of the tip gap increases, the average heat transfer coefficient on the flat tip first increases then decreases. For a cavity tip, areas of high local heat transfer coefficient on the tip were observed on the tip surfaces where the tip leakage flow reattaches. At tip gaps smaller than 1.6% chord, the average heat transfer coefficient on the cavity tip decreases significantly if the tip gap decreases. The cavity tip has a lower average heat transfer coefficient than the flat tip at tip gaps smaller than 2.5% chord. However, because the surface area of the cavity tip is 1.38 times that of the flat tip, the cavity tip has a higher thermal load than the flat tip at all of the tip gaps studied.