Measurement and analysis of gas turbine blade tip heat transfer

To achieve higher thermal efficiency and thrust modern gas turbine engines operate at high combustor outlet temperatures of 1300–1500C. Turbine blades are exposed to these high temperature gases and undergo severe thermal stress and fatigue. Blade tips are the most critical regions, typically difficult to cool, and are subjected to potential damage due to this high thermal load. Therefore, accurate information of heat transfer coefficient on the blade tip and tip leakage flow is important. This study presents detailed heat transfer coefficient and static pressure distributions on a gas turbine blade tip in a five-bladed stationary linear cascade. Both plane and squealer tips are considered. The effect of tip clearance and turbulence intensity on leakage flow and heat transfer is experimentally investigated for both plane and squealer tips. The effect of squealer tip cavity recess and squealer tip geometry on leakage flow and tip heat transfer is also investigated. A transient liquid crystal technique is used to present detailed heat transfer coefficient distribution. The blade used here is a 2-dimensional model of a first stage gas turbine rotor blade with a blade tip profile of a GE-E3 aircraft gas turbine engine rotor blade. The flow condition in the test cascade corresponds to an overall pressure ratio of 1.32 and an exit Reynolds number based on axial chord of 1.1 × 106. Static pressures are measured in the mid-span and the near-tip regions as well as on the shroud surface, opposite the blade tip surface. Local heat transfer coefficients and shroud static pressure distributions are presented for both plane and squealer tips. Results show various regions of high and low heat transfer coefficient on the tip surface. A squealer tip provides a lower heat transfer coefficient on the cavity surface than a plane tip case. An increase in tip clearance increases the leakage flow and heat transfer coefficient. An increase in turbulence intensity increases the heat transfer coefficient along the leakage flow path. A separated or open squealer performs better than a regular enclosed squealer. A squealer on the suction side performs better than that on the pressure side of the blade.