收缩-扩张形气膜孔提高气膜冷却效率的机理研究

为了揭示收缩-扩张形孔提高气膜冷却效率的机理,选择了两种典型的气膜孔:圆柱形孔和扇形孔,进行了数值模拟对比研究.湍流模型选取Realizable k-ε模型,壁面函数采用增强壁面函数.结果表明:圆柱形孔射流法向动量很大很集中,生成了较强的耦合涡,冷却效率最低;扇形孔减弱了射流的法向动量,并产生了一定的展向速度,冷却效率得以提高;收缩-扩张形孔减小了射流的流向厚度,增大了射流的展向宽度,且产生了更大的展向速度,扩大了射流的覆盖区域,形成了与圆形孔及扇形孔射流相比作用相反的耦合涡,使气膜更好地贴附于壁面,气膜冷却效率高于其它两种孔形的效率;相对于圆柱形孔和扇形孔,收缩-扩张形孔的平均气膜冷却效率,在吹风比为0.5时,分别提高了约110%和15%,在吹风比为2时,分别提高了约560%和60%. 

Study on the physics of film-cooling effectiveness enhancement by the converging-expanding hole

Numerical simulation was carried out to investigate the flow fields for three types of shaped hole,namely,cylindrical hole,fan-shaped hole and converging-expanding hole,to reveal how the converging-expanding hole enhance the cooling effectiveness.Realizable k-ε turbulence model with enhanced wall function was used.Results show that the jet from cylindrical hole produces strong streamwise coupling vortices due to its strong and concentrated normal momentum.The fan-shaped hole improves the cooling effectiveness by weakening the jet's normal momentum and the coupling vortices.The converging-expanding hole reduces flow separation in the hole and produces a jet with small streamwise thickness and large lateral width as well as large lateral velocity magnitude.These factors make its coupling vortices have an effect to push the jet to the wall,producing the best coverage and the best cooling effectiveness.The average cooling effectiveness of converging-expanding hole is larger than cylindrical hole's and fan-shaped hole's by about 110%and 15%respectively(M=0.5),or 560%and 60%(M=2).