Numerical Simulation of Continuous and Pulsed Film Cooling on a Turbine-Blade Leading-Edge Model, including Surface Conductance

Abstract

This study is a three-dimensional numerical investigation of the effectiveness of film cooling for a turbine blade leading-edge model with both a single and a three-hole cooling configuration. The model consists of a half cylinder with a flat after-body, and has the same dimensions as those in the experimental investigation of Ou and Rivir (2006). The single coolant hole is situated approximately at the span wise center of the cylindrical segment, and makes an angle of 21.5 degrees to the leading edge and 20 degrees to the span wise direction. For the three-hole configuration, the center hole is positioned the same as the single hole in the single-hole configuration, with the adjacent holes located at a span wise distance of 37.4 mm on either side of the center hole. Multi-block grids were generated using GridGen, and the flows were simulated using the flow solver Fluent. Simulations were carried out for blowing ratios, M, ranging from 0.75 to 2.0. Turbulence was represented using the k-ω shear-stress transport (SST) model. Results are obtained for two types of wall-boundary conditions: an adiabatic wall, and a conductive wall. The adiabatic-wall results overpredicted the film-cooling effectiveness in the far downstream region for low blowing ratios. Also, in the vicinity of the cooling hole, an increase in blowing ratio resulted in higher film cooling effectiveness than observed in the experiments. The conductive-wall results show a much closer agreement with experimental data for film effectiveness as compared to the adiabatic-wall predictions. Finally, a novel concept of pulsing the coolant flow was implemented so as to achieve film-cooling effectiveness equivalent to that with constant cooling, but with reduced overall coolant air, thereby enhancing turbine efficiency. Pulsed cooling with pulsing frequency PF = 5 and 10Hz, and duty cycle DC = 50%, shows the greatest cooling effects. The three-hole cooling results indicate that the 49mm span wise distance used for computing the span wise-averaged values for film-cooling effectiveness accounts for all of the film-coolant spreading provided by the single hole. span wiseThe most significant new finding in this work is that the inclusion of wall conductance is critical for reproducing the experimental data.