Film cooling characteristics of converging-expanding hole with transient liquid crystal measurement technique

Film cooling characteristics of a converging-expanding hole were measured using a transient liquid crystal measurement technique which could process nonuniform initial temperatures. The impact of momentum flux ratio was tested, and comparison was carried out between the converging slot-hole and cylindrical hole. The results show that the film cooling characteristic distributions of a converging-expanding hole are quite different from those of cylindrical holes because of their different flow structures. Jets from the converging-expanding hole cover the entire downstream surface. And the cooling effectiveness in the hole centerline region is greater than that in the region between adjacent holes for a converging-expanding hole. In the upstream region, interaction of adjacent jets enhances heat transfer in the region between adjacent holes for a converging-expanding hole. However, in the downstream region the couple vortices make heat transfer lower than that in the centerline region. Under the same momentum ratios, the average normalized heat transfer coefficient of the converging-expanding hole is larger than that of a cylindrical hole in the upstream, but lower in the downstream. The laterally averaged effectiveness of the converging-expanding hole is much larger than that of the cylindrical hole, and it reaches its highest value when momentum flux ratio I=2.