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

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.