超声速气流中扩张孔横向射流冷却特性研究

Cooling Characteristics of Transverse Jets With Expansion Holes in Supersonic Flow

考虑真实情况下孔内流动非均匀性,本文建立大腔供气下超声速离散孔气膜冷却模型,以马赫数为1.4工况下开展了单排圆柱孔和扩张扇形孔气膜冷却大涡模拟研究,对比分析不同孔型在不同吹风比时气膜有效度及流动掺混结构。结果表明,吹风比较小时,由于射流较弱的动量特性,孔出口附近不易出现显著分离吹飞,在超声速来流压迫作用下,近孔上游区域呈现较好的有效气膜特征,但沿下游发展过程,射流与主流掺混程度加剧;随着吹风比的提升,沿流向发展逐渐呈先升高后降低的变化规律。近壁处下洗涡对是影响超声速主流中离散孔气膜展向延伸效果不足的主要因素,射流受孔前诱导马蹄涡及中心对转涡诱导反向对转涡的共同耦合制约;展向扩张角能够有效增强离散孔气膜的展向铺展范围,但对提升气膜的流向延伸性效果不足。

Considering the nonuniformity of the flow characteristics in the holes under real conditions,a supersonic film-cooling model of discrete holes fed by a stagnant plenum is established in the present study.A large-eddy simulation of film cooling with single-row cylindrical holes and fanshaped holes was carried out under a freestream Mach number of 1.4.The film cooling effectiveness and fow mixing structure at different blowing ratios were compared and discussed.The simulation results show that there is no obvious jet lift-off near the hole outlet when the blowing ratio is small due to the weak momentum characteristics of the jet.Under the action of supersonic freestream pressure,the upstream region presents highly effective film characteristics;however,the mixing degree of the jet and the freestream is intensified along the downstream development process.With the increase in the blowing ratio,the development along the fow direction gradually shows a change pattern of first increasing and then decreasing.The downwash vortex pair near the normal wall is the main factor affecting the insuffcient extension effect of the discrete-hole flm in the supersonic freestream,and the jet is constrained by the joint coupling of the horseshoe vortex induced in front of the hole and the reverse counter-rotating vortex induced by the center vortex pair.The lateral spreading angle can effectively enhance the spanwise film-coverage range of discrete holes,while it is not enough to improve the film extensibility in the flow direction.