The Influence of Density Difference Between Hot and Coolant Gas on Film Cooling by a Row of Holes: Predictions and Experiments

Abstract

The two-dimensional boundary-layer procedure of Schönung and Rodi [1] for calculating film cooling by a row of holes was extended to account for density differences between hot gas and injected coolant gas. The extensions concern the injection model for leaping over the immediate blowing region in the boundary-layer calculation and also the dispersion model for taking into account three-dimensional effects. The extended model is tested for a density ratio of ρj /ρe ≈ 2 for both flat-plate situations and film cooling on a model turbine blade. The predicted laterally averaged film cooling effectiveness is compared with measurements for these cases. Results for the flat-plate experiments were taken from the literature, while experiments for a model turbine blade are also described in this paper. For a fixed injection angle of 32 deg, the film cooling effectiveness was measured for various spacings and velocity ratios Uj /Ue . The density ratio ρj /ρe ≈ 2 was achieved by adding Freon to the injection gas. The results are compared with those reported in [2] for negligible density difference. At the same blowing rate M = Uj /Ue , the film cooling effectiveness was found to increase with the density ratio ρj /ρe . In general, the influence of the density difference is well predicted by the model.