Film-Cooling Performance with Various Hole Length to Diameter Ratios for Cylindrical and Laidback Fan-Shaped Holes with an Inlet Groove

The influence of the hole length-to-diameter ratio on film-cooling performance is numerically investigated for a cylindrical hole and laidback fan-shaped hole with an inlet groove. Numerical analysis of film-cooling is conducted by solving three-dimensional Reynolds-averaged Navier-Stokes equations (RANS) with a Realizable k-ε turbulence model. Rectangular and triangular grooves are applied to the inlet of cylindrical and laidback fan-shaped holes. The ratio of the hole length (L) to the diameter (D), i.e., L/D, is varied between 6–12 at blowing ratios (M) of 0.5 to 1.5 for the cylindrical hole and 0.5 to 3.0 for the laidback fan-shaped hole. For cylindrical holes with an inlet groove, the film-cooling effectiveness decreases as the L/D increases, regardless of the blowing ratio. However, in the case of laidback fan-shaped holes, the cooling performance with the length-to-diameter ratios shows different tendencies for each blowing ratio. At low blowing ratios (M=1.0), relatively high effects were observed with more than 5% increases in the effectiveness at L/D=10 and 12 compared to that of L/D=6. However, the performance is maximized at L/D=8 under high-blowing-ratio conditions (M=3.0). The cooling efficiency is enhanced up to 148% for square grooves and 124% for triangle grooves compared to those of L/D=6.