Heat transfer measurements in turbines

Abstract

A blowdown turbine facility and an experimental program for the study of heat transfer in cooled turbines are described. The blowdown facility introduces the concept of using short duration experiments to test turbines by scaling the metal surface temperatures down to room temperature, and consequently scaling pressures and mass flow rates so that Reynolds, Mach and Prandtl numbers are kept unchanged. Hence, the Nusselt number is also unchanged. The short operating time assures that the surfaces remain nearly isothermal and that fast instrumentation, pressure transducers and thin film gauges can be used to record average and unsteady pressures and heat transfer. For example, the instrumentation is able to resolve heat transfer and pressure fluctuation induced by rotating blades passing over the stationary shrouds. Both the operation and demonstration runs of the blowdown facility are described. Finally, a two dimensional steady flow film cooling experiment yields heat transfer coefficients under conditions which model the average tangential flow over the stationary shrouds of the turbine under test in the blowdown facility. The results indicate that the curvature of the shroud leads to an increase of heat transfer by 15% and the separation of the coolant flow at the injection edge reduces the cooling effectiveness just downstream of the injection slot.