Numerical investigation of mist-assisted film cooling characteristics for sister holes under various side-hole inclination angles and droplet diameters

Increasing the turbine inlet temperature improves the thermal efficiency of gas turbines while simultaneously increasing the thermal load on internal high-temperature components. Therefore, cooling technologies that enhance cooling performance without requiring additional cooling air need further investigation. This study employed numerical methods to investigate the application effects of combining mist injection with sister holes. The Euler-Lagrange method was used to couple the continuous gas-water-vapor phases with discrete droplets. The SIMPLEC pressure-velocity coupled solver based on the realizable k-ε turbulence model with enhanced wall treatment, combined with a second-order upwind discretization scheme was adopted. The prediction results were validated against published experimental data on sister holes and mist cooling experiments. The flow characteristics and the film cooling effectiveness of sister holes were investigated under four side-hole inclination angles ( β = 30°, 60°, 90°, 120°), three droplet diameters ( d p = 10 μm, 20 μm, 30 μm), and three blowing ratios ( M = 0.5, 1.0, 1.5). The results show that when M = 0.5, mist-assisted film cooling increases the average surface film cooling effectiveness by 17.7%–30.6% compared to pure air cooling. Droplets with a diameter of 10 μm flow with the coolant and remain close to the wall, whereas larger droplets are lifted upward, thereby reducing the wall cooling effectiveness. As the blowing ratio increases, a sister hole configuration with β = 30° provides more persistent downstream protection. Side-hole inclination angles of 60° and 90° enhance resistance to counter-rotating vortex pair (CRVP) and improve coverage near the holes and the spanwise direction. However, the reverse jet with β = 120° intensifies mixing, leading to a rapid deterioration in downstream cooling effectiveness. The results of this study provide a reference for selecting the sister hole configuration, droplet diameter, and blowing ratio in the design of gas turbine film cooling technology.