Numerical simulations of film cooling under the condition of subsonic mainstream in convergent channel

expanded channel and straight channel were conducted. The flow fields and temperature fields of the mainstream and secondary streams were investigated under different streamwise pressure gradients and different flow blowing radios. The results showed that the mainstream boundary layer thickness

mixing intensity of shear layer and the counter-rotating vortex pair intensity and distributions were the main factors contributing to the changes of the film cooling effectiveness. Compared with the zero pressure gradient case

adverse pressure gradient increased the boundary layer thickness and strengthened the penetration of the secondary flow for the low blowing ratio (M=0.25) cases. Meanwhile

the intensity of the counter-rotating vortex pair was weak. As a result

the averaged film cooling effectivenesd increases by 4.91% at the low blowing ratio. For the high blowing ratio case (M=2)

favorable pressure gradient restrained the development of mainstream boundary layer and depressed the penetrating ability of the secondary flow. At the same time

the accelerated mainstream made the counter-rotating vortex pair closer to the wall. These caused the film cooling effectiveness increase by 17.40% at the high blowing ratio.