A fundamental study of high pressure turbine blade trailing edge cooling: an experimental and numerical approach.

Abstract

Experimental and computational results regarding turbulent mixing of passage flow and the coolant from a high-pressure turbine blade trailing edge cooling scheme are documented. Special interest is devoted to gaining a fundamental understanding of the thermal protection provided by the cooling scheme. The trailing edge cooling scheme is a scaled version of a generic scheme, tested in a suction type wind tunnel. The scaled model is three-dimensional with rectangular ribs. Three different lip geometries (square, single round, and double round) are tested. The freestream Reynolds number, based upon the lip thickness, is fixed at 10,200. Primarily, three blowing ratios, M=1.5, M=1.0, and M=0.5 are documented. A hot-wire sensor and a thermocouple are placed inside the slot and detailed measurements of velocities, turbulence intensities, and temperatures are acquired. Values of adiabatic effectiveness obtained on the model surface quantify thermal protection. Spectral analysis of the hot-wire signal is performed at various locations in the flow field. Spectra indicate a coherent mechanism of mixing. This clear unsteadiness is attributed to vortex shedding from the lip. It is shown that effectiveness increases as the blowing ratio increases. This document suggests also that lip geometry is an influential parameter for this cooling scheme. Effectiveness is greatly increased when a rounded lip is utilized. In one case, additional blowing ratios (M=0.75 and M=1.25) were tested. Experiments concluded that above M=1.25, effectiveness is insensitive to blowing ratio. Two-dimensional simulations are presented for M=1.5, M=1.0 and M=0.5. They use various Reynolds Averaged Navier Stokes turbulence closure models. The frequencies of unsteadiness are well modeled but, in general, effectiveness is over-predicted. Furthermore, general features of the flow and thermal fields are modeled well, but surface heat transfer characteristics are not.