主流压力梯度对气膜冷却效率影响的数值研究

Numerical research on film cooling effectiveness with different mainstream pressure gradient

分别对收缩通道、扩张通道和直通道中亚声速主流条件下的气膜冷却进行数值模拟,对比分析了不同主流压力梯度、次流吹风比条件下的主流和次流流场、温度场特征。研究结果表明:引起气膜冷却效率变化和不同发展趋势的因素可归结为主流边界层厚度、主次流自由剪切混合程度、肾形涡的强度和位置等因素。相对于零压力梯度的主流条件,在吹风比较小(M=0.25)的情况下,主流的逆压力梯度一方面增厚边界层、增强了气膜射流对主流的穿透,另一方面减小了肾形涡的强度,综合作用的结果是气膜平均冷却效率提高了4.91%。在吹风比较大(M=2)的情况下,主流的顺压力梯度扼制主流边界层的发展、抑制气膜射流的穿透能力,降低肾形涡涡核的位置,从而提高气膜冷却效率达17.40%。

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 gradieht 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.