Large eddy simulation of film cooling flow from converging slot-holes

Large eddy simulation (LES) was performed for film cooling from converging slot-holes (consoles) at different blowing ratio of M = 1.0-3.0, and the Reynolds number, Re = 21719, based on the mainstream velocity and inlet hole diameter. In time-averaged flow fields of film cooling, counter-rotating vortex pairs (CRVPs) and anti-CRVPs are dominant structures. CRVPs result in the deterioration of film cooling performance, while the effect of anti-CRVPs is opposite. Instantaneous coherent structures for consoles including jet vortex pairs, anti-jet vortex pairs, hairpin vortexes, and leading- and trailing-edge vortexes were analyzed in detail. Jet vortex pairs are firstly generated in consoles, and then enter the mainstream channel, finally evolve into hairpin vortexes. The head, horizontal leg and vertical leg of hairpin vortexes correspond to roller vortexes, CRVPs and upright wake vortexes respectively. Anti-jet vortex pairs are the sources of anti-CRVPs. By time-frequency analysis of pressure signals, it was found that the signals from downstream of the hole centerline exhibit periodicity. The dominant frequency always increases with the increase of the blowing ratio, however, the corresponding amplitude of power spectrum increases firstly, and then decreases.