Cooling the tip of a turbine blade using pressure side holes - Part 1: Adiabatic effectiveness measurements

Sealing and durability for turbine blade tips have been challenging problems since the development of gas turbine engines. Blade tip designs are extremely important in terms of sealing and engine performance. In general, overall engine performance can be improved by increasing turbine inlet temperatures. As a result, cooling methods along the blade tip need to be devised and applied effectively. Film-cooling is typically used as a blade tip cooling method, whereby coolant is supplied through holes placed along the pressure side of a blade. Experiments were conducted in a linear cascade with a scaled-up turbine blade whereby the Reynolds number of the engine was matched. A range of blowing ratios was studied whereby coolant was injected from holes placed along the pressure side tip of the blade as well as from dirt purge holes placed on the blade tip. This paper, which is Part 1 of a two part series, compares adiabatic effectiveness levels measured along a blade tip, while Part 2 combines measured heat transfer coefficients with the adiabatic effectiveness levels to assess the overall cooling benefit of pressure side blowing near a blade tip. The results show better cooling can be achieved for a small tip gap compared with a large tip gap with different flow phenomena occurring for each tip gap setting.