Effect of mainstream Mach number on the flow characteristics and cooling effectiveness of supersonic film cooling

Abstract

For supersonic film cooling, the interaction between the mainstream and coolant jet will influence the flow characteristics near the film cooling hole as well as the film cooling performance. To evaluate the influence mechanism of mainstream Mach numbers on the flow field structure and film cooling effectiveness, numerical simulations are performed under various mainstream Mach number conditions (Ma∞ = 0.8, Ma∞ = 2, and Ma∞ = 4). As the obstructing effect of the coolant jet, the complicated shock waves are induced upstream of the film cooling hole under the supersonic mainstream condition. Due to the influence of the oblique shock waves, the mainstream moves away from the central area along the spanwise direction, which results in diminishing of the interaction between the mainstream and the coolant. For supersonic mainstream condition, the secondary counter-rotating vortex pairs (SCVP) are induced in the outer area of the primal counter-rotating vortex pairs (PCVP), which weakens the action of the mainstream on PCVP and slows down the weakening of the vortex. The emergence of SCVP weakens the vertical diffusion of PCVP, while increasing the spanwise dimension of PCVP, resulting in better film flow adhesion and greater spanwise film coverage. Additionally, due to the shock waves induced uneven distribution of the static pressure occurs near the exit of the film cooling hole. The unevenness of the static pressure distribution increases with the mainstream Mach number, resulting in a relatively high mass fraction of the coolant at the leeward side of the film cooling hole. It is indicated that for supersonic mainstream condition, the mixing and dissipation of the coolant are diminished, leading to an enhancement in the film cooling performance at the downstream of film cooling hole. The film cooling effectiveness increases as the mainstream Mach number increases.