Turbulence Measurements in Turbine Blade Passages and Implications for Heat Transfer

This paper describes a program of research in which, by using laser-Doppler anemometry, the variations of artificially induced flow perturbations to represent turbulence in an engine have been measured through the passages of a cascade of modern turbine blades. Although based upon commercially available laser-Doppler equipment, the special problems of making reliable and reproducible measurements in the demanding flow conditions of highly loaded turbine blades required special facilities in the apparatus and these are briefly described in the paper. The results themselves provide some confirmation of the common—but hitherto unjustifiable—assumption that the absolute level of velocity fluctuation remains essentially constant as the time-mean velocities change significantly. The results also show significant departures from this assumption, especially on the forward suction surface and near the leading edge. These observations throw some light upon the observed variation in the distribution of convective heat transfer rates to blades in the highly unsteady conditions which characterize the flows in the real turbine, compared with the idealizations of many experimental and theoretical simulations.