Numerical study on unsteady film cooling performance under the mainstream swing condition

Significant unsteady film cooling performance of a turbine shroud can be found under the periodic disturbance of rotor blades. The mainstream flow in film cooling on a turbine shroud is simplified as the periodic swing based on the alternate appearance of the cascade passage flow and the blade tip clearance flow. Three-dimensional unsteady numerical simulation was employed to analyze the film cooling effectiveness with a single cylindrical hole injection at mainstream swing frequencies of 100, 160 and 220 Hz, and at blowing ratios of 0.5, 0.8, 1.1 and 1.4, respectively. A steady simulation was also carried out as a comparison. The results show that mainstream swing provides instantaneous film spots. It is a novel phenomenon in film cooling. Spanwise coverage of film was more uniform compared with the steady case. There are considerable differences of film cooling effectiveness under the various mainstream swing frequencies. A larger swing frequency results in higher spanwise averaged time-averaged film cooling effectiveness.