Cooling the Tip of a Turbine Blade Using Pressure Side Holes—Part I: Adiabatic Effectiveness Measurements

Abstract

Durability of turbine blade tips has been and continues to be challenging, particularly since increasing turbine inlet temperatures is the driver for improving turbine engine performance. As a result, cooling methods along the blade tip are crucial. Film-cooling is one typically used cooling method whereby coolant is supplied through holes placed along the pressure side of a blade. The subject of this paper is to evaluate the adiabatic effectiveness levels that occur on the blade tip through blowing coolant from holes placed near the tip of a blade along the pressure side. A range of blowing ratios was studied whereby coolant was injected from holes placed along the pressure side tip of a large-scale blade model. Also present were dirt purge holes on the blade tip, which is part of a commonly used blade design to expel any large particles present in the coolant stream. Experiments were conducted in a linear cascade with a scaled-up turbine blade whereby the Reynolds number of the engine was matched. 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 much 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.