Turbulent Transport in Film Cooling Flows

Abstract

This experimental study was performed on a single row of round holes with a 35° surface angle, representing film cooling geometry commonly used in turbine engines. Simultaneous velocity and temperature measurements were made using a cold-wire in conjunction with a LDV. The experimentally determined cross correlations provide a direct indication of the extent of turbulent transport of heat and momentum in the flow, which in turn governs dispersion of the film cooling jet. Actual engine environments have elevated mainstream turbulence levels that can severely reduce the cooling capability of film cooling jets. Clearly, the turbulent transport for very high mainstream turbulence is expected to be markedly different than that with low mainstream turbulence, and would improve our understanding of the mechanisms involved in the dispersion of film cooling jets. Experimental cross-correlation data was obtained for two vastly different freestream turbulence levels (0.6% and 20%) in this study. For this purpose, eddy diffusivities for momentum and heat transport were estimated from the measured data. These results will help develop new turbulence models and also explain why gradient diffusion based models do not give good predictions relative to experimental results.