出/入口面积相等的收缩-扩张孔气膜冷却特性

Film cooling characteristics of converging-expanding hole with equal exit-entry area

关键词:  气膜冷却  收缩扩张形孔  瞬态测量  冷却效率  换热系数  流量系数

Key words:  Film cooling  Converging-expanding hole  Transient measurement  Film cooling effectiveness  Heat transfer coefficient  Discharge coefficient

摘要:

采用一种可进行全表面测量的瞬态液晶测量技术测量了一种出口面积与入口面积相等的收缩扩张形孔的气膜冷却特性,研究了动量比(0.5,1,2,4)的影响,并与传统的出口面积小于入口面积的收缩扩张形孔的气膜冷却特性进行了对比。结果表明:收缩扩张形孔射流均完全覆盖了孔下游壁面,射流的交汇以及对涡结构使得孔中心线附近区域的冷却效率较低,而孔间区域的冷却效率较高。在上游区域,孔间区域的换热系数比相对孔中心线附近区域的较高,而在下游区域,对涡结构又使得孔间区域的换热系数比相对较低。出口-入口面积比不同的两种收缩扩张形孔的冷却效率分布规律和换热系数比分布规律都比较相似,但出口-入口面积比为1的收缩扩张形孔的冷却效率以及上游区域的换热系数比的数值都相对较低。而且出口-入口面积比为1的收缩扩张形孔的流量系数明显高于出口-入口面积比小于1的收缩扩张形孔。

Abstract:

Film cooling characteristics of converging-expanding hole with equal exit-entry area are measured using a transient liquid crystal measurement technique which can process nonuniform initial temperature. The momentum flux ratios tested are 0.5, 1, 2, 4,respectively. And comparison with traditional converging-expanding hole with smaller exit area is carried out. The results show that jets from converging-expanding holes cover the entire downstream surface. The couple vortices formed by interaction between jet and mainstream decrease the effectiveness in the hole centerline region, but increase the effectiveness in the region between adjacent jets. In the upstream region, interaction of adjacent jets enhances heat transfer in the region between jets. However, the couple vortices make the normalized heat transfer coefficient of the region between jets decrease gradually and lower than that of the centerline region in the downstream. The distribution features of the cooling effectiveness and the heat transfer coefficient are very similar for the two kinds of converging-expanding holes with different exit-entry area ratios. But the converging-expanding hole with equal exit-entry area produces lower effectiveness in the whole region and lower heat transfer coefficient in the upstream region than the hole with smaller exit area. The discharge coefficients of the hole with larger exit area are much higher than those of the traditional converging-expanding hole with smaller exit area.