Film cooling and aerodynamic performances of a turbine nozzle guide vane with trenched cooling holes

Highlights: • The practicability of segmented trench film cooling is thoroughly studied. • Offset of coolant density and vortex cores benefits the novel trench cooling. • The novel trench cooling fits for low curvature surface on vanes. • Trenched film holes generate lower flow resistance than cylindrical holes. -- Abstract: The numerical investigation on shaped trench film cooling was carried out using Reynolds averaged Navier-Stokes simulation to test its practical utility. The cooling performance of three kinds of film holes (standard cylindrical film holes, transverse trenched and segmented trenched film holes) on a flat plate was studied firstly to verify the numerical method and illustrate the vortex structures in detail. Then the cooling characteristics of the three kinds of film holes, which are located at five single row positions around a turbine vane, were compared in operating conditions. The parameters of adiabatic film cooling effectiveness, discharge coefficient and total pressure losses are analyzed with the blowing ratios from 0.5 to 3.0, and the optimal position on turbine vanes for the novel trenched film hole was confirmed. The results show that the trenched cooling holes produces more uniform coolant distribution laterally at all positions, leading to higher cooling performance particularly at high blowing ratios. The unique vortex configuration generated by segmented trench shows clear advantages at the small curvature positions on the pressure side, where the mainstream influence is minimum and is more suitable for the novel structure. The flow resistances in trenched film holes are less than that in cylindrical holes. The magnitude of the total pressure losses of the three cooling holes are almost the same.