Numerical analysis of flat plate film cooling characteristics at various streamwise angles based on plasma actuation

Large eddy simulations(LES) were carried out to numerically investigate the effects of streamwise angles on the film cooling performance with and without plasma actuation. Results showed that as the streamwise angle increased, the coolant penetrated deeper into the crossflow, thus the reverse flow region downstream the jet grew in size, and the strength and the liftoff effect of the hairpin vortex increased, resulting in a reduction of film cooling efficiency, but at 90° angle the film cooling efficiency slightly increased since some cold fluid was entrained into its wake. As a result, the film cooling efficiency was the highest at 35°angle and the lowest at 60°angle. Due to the downward momentum of plasma actuation, the penetration of the jet into the crossflow was depressed, the KuttaZhoukowski lift acted by the crossflow and on the head of the hairpin vortex was reduced, and the strength of the mutual induction between the feet of the hairpin vortex was decreased. Accordingly, the evolution and the liftoff effect of the hairpin vortex were suppressed, thus the film cooling efficiency was enhanced and these impacts were more significant at smaller streamwise angle. At the 35° angle the centerline film cooling efficiency increased by 55% at most.