带凹坑圆孔气膜冷却流动传热特性

利用大涡模拟方法对平板带凹坑气膜孔冷气射流与主流的相互作用展开研究，并结合红外热成像壁温测试和粒子图像测速结果进行实验验证，揭示了凹坑对气膜冷却的强化机理。结果表明:凹坑在气膜孔下游诱发反肾型涡对，将冷气向壁面卷吸，改善了气膜贴壁性；与圆孔气膜冷却相似，凹坑气膜冷却流场也出现马蹄涡、发卡涡等大尺度拟序结构，但与圆孔下游的单串列发卡涡不同，凹坑尾缘的“内凹”造型诱发两串并列的发卡涡，且发卡涡结构在大吹风比工况下也较圆孔稳定；脉动信号的频谱分析表明凹坑孔气膜冷却射流周期性弱，流场中低频振荡占主导作用。整体而言，凹坑造型增强了气膜射流的展向扩张，其冷却性能优于圆孔。 

Flow and heat transfer characteristics of round-hole film cooling with crater

The interaction between the mainstream and coolant flow from the crater hole on flat plate was studied by large eddy simulation method，and the film-cooling enhancement mechanism of crater hole was revealed.The simulation results were compared with the experimental results by infrared thermal imaging test and particle image velocimetry.The results showed that the crater hole generated a pair of anti-kidney vortices downstream the coolant exit，promoted the entrainment of coolant towards the wall and improved the coolant coverage.Compared with round hole，large-scaled coherent structures including hairpin vortices and horseshoe vortices can also be observed in crater-hole flow fields.However，different from round-hole，the concave effect on the trailing edge of crater generated parallel lines of hairpin vortices，presenting better stability at high blowing ratio.The time-frequency analysis of pressure fluctuation signals showed that the periodicity of crater-hole film cooling was weaker，and the small-frequency vortices played a dominant role.Overall，crater improved the lateral spreading of coolant jet，and its cooling performance was better than round-hole.