Anti-Kidney Pair of Vortices in Shaped Holes and Their Influence on Film Cooling Effectiveness

Abstract

The difference in film cooling effectiveness of three shaped holes is hereby explained by their vortical structures. Highlighted, in particular, are the competing effects of two pairs of vortices present in jets: the so-called kidney-shaped pair of vortices and a newly found anti-kidney pair. Three shaped holes investigated were referred to as TP2, TP3, and TP4. Except for the difference of how the hole area is increased, they are essentially the same. At the higher blowing ratio, the film cooling effectiveness of TP4 was found to be far superior to those of either TP2 and TP3. By flow visualization in water, the cause of these differences was investigated and found to be explainable on the basis of different vortical structures. In particular, for TP4 with a better film cooling effectiveness, the kidney- and anti-kidney pairs were found to cancel each other, leading to the improved jet attachment.