浅槽孔气膜冷却的大涡模拟研究

Large Eddy Simulation of Film Cooling from a Shallow Trench-Hole

关键词:  燃气涡轮发动机  气膜冷却  射流  孔形  大涡模拟  边界层  冷却效率

Key words:  Gas turbine engine  Film cooling  Jet flow  Shaped hole  Large eddy simulation  Boundary layer  Cooling effectiveness

摘要:

为了探究浅槽孔气膜冷却的强化冷却机理，针对平板浅槽型气膜孔冷却射流与主流相干作用进行大涡模拟研究，并与圆孔射流进行对比分析。研究结果表明：浅槽孔内部会形成一对循环涡旋，将冷却气向展向卷吸；浅槽孔下游会同时出现肾形涡对和反肾形涡对，反肾形涡对抑制了气膜冷却射流的抬升，改善了冷气贴壁性；与圆孔相比，浅槽孔气膜冷却射流的流场拟序结构分布更为无序，浅槽前缘未出现马蹄涡旋，射流下游也未形成串列的发卡涡；当吹风比增长到1.5时，浅槽孔在低频区（400Hz处）出现主频，在高频区的振幅则远低于圆孔，表明高吹风比下浅槽孔气膜冷却射流流场中低频小尺度涡旋占主导作用。整体而言，浅槽孔提升了气膜的展向扩展能力，冷却性能远优于传统圆孔。

Abstract:

Large eddy simulation（LES）was used to study on the interaction of the mainstream and secondary flow from the hole embedded in a shallow trench on a flat plate, which was compared with the cylindrical hole to reveal the enhanced heat transfer mechanism of film cooling from the shallow trench. The results show that circular vortex pair will be formed inside the shallow trench, leading to the entrainment of coolant gas toward the spanwise direction. The kidney vortex pair and the anti-kidney vortex pair will appear at the same time. The anti-kidney vortex pair suppress the uplift of the jet flow to improve its attachment. Compared with the round hole, the distribution of coherent structure in trench configuration jet flow fluid is more disorder. The horseshoe vortex does not appear on the leading edge of the shallow cavity, and the series of hairpin vortex are not formed downstream. When the blowing ratio rises to 1.5, the dominant frequency appears in low frequency region (at 400Hz) in the flow field after the shallow trench. The pressure pulsation signal oscillates stronger than cylindrical hole, while the amplitude in the high frequency region is much lower than round hole. The results indicate that small scale vortex with low frequency dominates the film jet flow field of trench hole. Overall, the shallow trench enhances the spanwise expansion of the film, and its cooling performance is much better than that of the traditional round hole.