Very Large Eddy Simulation of Film Cooling Effectiveness on Trailing Edge Cutback

The trailing edge of gas turbine blade in aero-engine is usually designed as thin as possible to achieve higher aerodynamic efficiency. As the modern gas turbine inlet temperature is continuous increasing, thermal stress in blade trailing edge region becomes much significant, resulting in possibilities of high temperature erosion and creep problems. Due to superior film cooling and excellent aerodynamic performance, trailing edge cutback is widely applied in high pressure gas turbine of aero-engine. However, film cooling effect on trailing edge cutback is significantly affected by the mixing process between mainstream and cooling flow. In order to reveal the unsteady flow structures and film cooling mechanisms in trailing edge cutback region, the present paper utilizes a Very Large Eddy Simulation (VLES) method to investigate the film cooling effect and coherent unsteadiness in trailing edge cutback region. Firstly, computational models of trailing edge cutback are built, and the VLES strategies for predicting the film cooling effect in trailing edge cutback region are proposed. The grid independent analysis and numerical method validations are carried out with the existing experimental data. At three blowing rations, the film cooling effectiveness distributions on cutback are computed and compared with the experimental data. The numerical accuracies between different steady and unsteady prediction methods are compared. The coherent unsteadiness in trailing edge cutback region is visualized and the resolution abilities between different methods are analyzed. The results show that the VLES method is able to capture the mixing process of trailing edge coolant flow. Compared with the DDES (Delayed Detached Eddy Simulation) method, VLES method filters most of the small vortices but still has a good accuracy in resolving the film cooling effect on trailing edge cutback. The periodic vortex shedding formed by the interactions between mainstream and coolant is the main factor that affecting the cooling performance on cutback. Film cooling effectiveness predicted by RANS (Reynolds-Averaged Navier-Stokes) equations combined with four turbulence models (standard k-ε turbulence model, standard k-ω turbulence model, SST k-ω turbulence model, and SSG Reynolds stress model) are particularly higher than the measurements. Compared with URANS (Unsteady Reynolds-Averaged Navier-Stokes) and SAS (Scale-Adaptive Simulation) methods, the VLES method has a higher accuracy in resolving the periodic vortex shedding and film cooling effectiveness predictions. Compared with three DES (Detached Eddy Simulation) methods, i.e. conventional DES, DDES and SBES (Stress-Blended Eddy Simulation), VLES method has a comparable accuracy in capturing the vortex developments and mixing process in trailing-edge cutback region.