Simulation of film cooling heat transfer and simulation improvement with a modified DES turbulence model

Modeling the heat transfer characteristics of the highly turbulent flow in gas turbine film cooling is important for better engineering solutions to the film cooling system design. URANS, LES, DES and modified DES models capability in simulating film cooling with a density ratio of 2.0 and blowing ratio of 1.0 are studied in this work. Detailed comparisons of simulation results with experimental data regarding the near-field and far-fields are made. For near field predictions, DES gives decent prediction with a 21.4 % deviation of centerline effectiveness, while LES and URANS have deviation of 33.6% and 51.2% compared to the experimental data. Despite good predictions for near field, DES under predicts the spanwise spreading of counter rotating vortex pair and temperature field, therefore it over predicts the centerline effectiveness in the far field. To compensate for this shortcoming of DES, the eddy viscosity in the spanwise direction is increased to enhance spanwise-diffusion of the cooling jets. The modified DES prediction of overall centerline effectiveness deviates 12.4% from experimental data, while LES, unmodified DES and URANS predictions deviate 10.8%, 31.9% and 46.9%. The modified DES model has adequate predictions of vortices evolutions which URANS modeling lacks and consumes significant less computational time than LES. It can be said that the modified DES model results in satisfactory film cooling modeling with a moderate computational cost and time.