Large-Eddy Simulation of Film Cooling Performance Enhancement Using Vortex Generator and Semi-Sphere

Film cooling is an essential cooling method to prevent high-pressure turbine blade from melting down due to the high inlet temperature. In order to improve the film cooling efficiency, several flow control methods have been proposed. In this paper, large-eddy simulations (LES) are performed to study the effectiveness of a vortex generator (VG) and a semi-sphere installed downstream of the cooling jet. Before the detailed analyses, the numerical framework is validated against the available experimental data. Both laminar and turbulent boundary layers at the inlet are considered. The turbulent boundary layer is generated using a numerical plasma actuator immediately downstream of the inlet. The effects of VG and semi-sphere on the film cooling efficiency at various blowing ratios are analyzed. It is found that a counter-rotating vortex pair (CVP) is formed downstream of the cooling jet and its strength increases with the blowing ratio in the configuration with no VG/semi-sphere. When the VG is installed, it produces another vortex pair that rotates in the reverse direction of the counter-rotating vortex pair, which reduces the strength of the CVP and increases the lateral diffusion of the coolant. As a result, the film cooling efficiency is greatly improved, especially at a higher blowing ratio. For the case with a semi-sphere installed at the same location as the VG, the film cooling efficiency is also be improved, especially at low–medium blowing ratios. However, it is not as effective as the VG in terms of enhancing cooling efficiency. To examine the aerodynamic penalty associated the vortex generator and semi-sphere, the total pressure loss is calculated. It is found that the total pressure loss increased by only 1% due to the VG or semi-sphere, within the range of the blowing ratio investigated in the current study. Considering the overall performance and the feasibility of being applied in practice, a semi-sphere installed downstream of the cooling hole is a promising method to improve the cooling efficiency.