A novel design for film-cooling: Cooling holes with inlet groove

A novel film-cooling configuration, wherein a groove is integrated into the inlet of a film-cooling hole, is proposed herein, and its influences are investigated. 3D RANS simulations are conducted to compare the performance of the film-cooling hole with an inlet groove with that without a groove for three different hole shapes at a wide range of blowing ratios. The inlet groove enhances film-cooling in all cases except for the fan-shaped hole with a triangular groove at high blowing ratios and significantly affects the flow structure inside the holes. In the case of the cylindrical hole, the application of the triangular groove yields the most substantial performance enhancement. At M = 1.5, the spatially averaged film-cooling effectiveness experiences an approximate 100% improvement. For the fan-shaped hole and the laidback fan-shaped hole, the rectangular groove leads to the most pronounced improvement in performance. At M = 3.0, the spatially averaged film-cooling effectiveness experiences enhancements of around 8% and 30%, respectively. The reversal and strengthening of the in-hole counter-rotating vortex pair induced by the inlet groove promotes momentum mixing, reduces velocity imbalance, and decreases the coolant permeability. In some cases, the reversal of the jetting effect through the grooves may adversely affect the film-cooling effectiveness. Furthermore, the grooved inlet is shown to affect the film- cooling performance through multiple factors instead of a single factor.