Experimental and unsteady numerical investigations on cooling characteristics of trailing-edge cutback with effect of upstream film holes

This paper investigates the influence of film cooling characteristics of pressure-side film hole on trailing-edge cutback in the high-pressure vane of gas turbines. This paper employs the Pressure Sensitive Paint (PSP) technique and Particle Image Velocimetry (PIV) technique to obtain the time-averaged adiabatic film cooling effectiveness and details of the mixing region, respectively. Numerical simulations with the DDES turbulence model are also used to predict the flowfields. Two configurations are examined: one with a cutback without pressure-side film holes (Config A) and another with a cutback that includes pressure-side film holes (Config B). This paper investigates eight blowing ratios (Mslot = 0.3-1.2) of slot coolant in cutback for Config A and a suitable blowing ratio (Mhole = 0.4) of film holes for Config B, using both experimental and numerical methods. The results of both experiments and simulations for Config A and B show good agreement and reveal a non monotonic trend of film cooling effectiveness with increasing blowing ratio. The non-monotonic trend observed in Config A is attributed to an increase in the velocity gradient in the boundary layer on the coolant side with increasing blowing ratio, which leads to a different shedding vortex structure. The results for Config B show that the coolant from the pressure-side film holes changes the mixing structure downstream of the lip by rebuilding the mainstream's shear layer on the mainstream side. Adiabatic film cooling effectiveness increases significantly under low and moderate slot blowing ratios, but non-monotonicity is maintained. The Fast Fourier Transform method is used to investigate the impact of the jet stream, which affects only the area downstream of the film holes, while other regions along the pitch-wise direction are less affected. This paper also attempts to combine the effectiveness empirical correlations of 2D slot and film holes using the superposition model to quantitatively analyze the deterioration of cooling effectiveness resulting from the mixing of coolant and mainstream.