Investigation of Film Cooling Vortical Structures Behind a Cylindrical Hole Fed by an Internal Crossflow

Abstract

The film cooling vortical structure behind a cylindrical hole fed by internal crossflow was investigated by large eddy simulation (LES). The simulation was performed on a single simple cylindrical hole (i.e., a spacing of 3D, an entry length of 6.5D, and an injection angle of 35 o). Two blowing ratios (M = 0.40 and 0.80) were simulated with a density ratio of 0.97. The results were validated in comparison with the measured data. The vortical structures were identified by the Q-criterion coherent isosurface and their unsteady signatures were identified by the standard deviation (SD). The vortical structures were demonstrated to play the main role in cooling performance and its instability. The internal flow was significantly produced a vortex tube structure, which responsible for the shear vortex (Kelvin-Helmholtz instabilities) between the coolant and the mainstream at the hole exit. As a result, it forced the legs of the counter-rotating vortex pair (CRVP) to widely spread and enhance the coolant effectiveness downstream.