Film cooling performance evaluation of bi-directional diffusion hole with compound-angle on turbine blade: Study on spanwise width

A bi-directional diffusion hole configuration, which expands along the flow direction and blade tip with a compound-angle, is proposed based on an actual turbine blade in the present study. The turbulence model was adjusted to enhance simulation accuracy by correcting the turbulent viscosity coefficient, significantly improving the prediction of jet diffusion in mixing areas. The film cooling effectiveness distribution was studied through pressure-sensitive paint (PSP) experimental measurements. The effect of the hole outlet spanwise width on the bi-directional diffusion hole film cooling performance is characterized by a significant influence, non-monotonicity and weak coupling. The optimal hole outlet spanwise width of bi-directional diffusion holes is explored. The dimensionless temperature distribution and vortex structure of the fluid in the hole outlet section reveal the intrinsic mechanism of the effect of the hole outlet spanwise width on the film cooling characteristics. The numerical simulation results and experimental validation results show that the optimal hole outlet spanwise width of the bi-directional diffusion hole is approximately 4.3D with the goal of achieving the optimal level of film cooling effectiveness. Considering the flow blending situation, the optimal hole outlet spanwise width is determined by balancing the increase in film cooling effectiveness caused by the coolant film spreading covering mode and the decrease in film cooling effectiveness caused by mainstream intrusion. Therefore, the engineering applicability of the optimal hole outlet spanwise width as a design criterion for bi-directional diffusion holes of the turbine blade is demonstrated.