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.

Large-Eddy Simulation of double-row compound-angle film cooling: Setup and validation

“…Fig. 1b, hot air is fed towards the plate and the vortex pair tends to lift off from the plate [5]. If the hole additionally has a spanwise yaw angle b -0, cf.…”

Flow Visualization of Multi-Hole Film-Cooling Flow under Varying Freestream Turbulence Levels

“…In such a case, a counter rotating vortex (CRV) pair is created inside of the jet, which reduces the cooling effectiveness because of the entrainment of hot gases from the free stream flow to the wall surface. This phenomenon is described schematically by Haven et al [14] and can be seen in Figure 9.…”

“…As the flow progresses downstream, the downwash created by the main Figure 9. Diagram depicting the Counter Rotating Vortex (CRV) [14]. hole jet vortex (CRV) is reduced by the counter vortices generated by the side holes, which results in improved cooling coverage at all streamwise locations, especially downstream, as shown in Figure 11.…”

Film cooling sensitivity of laidback fanshape holes to variations in exit configuration and mainstream turbulence intensity

“…According to Thole et al [3], the diffuser shaped holes have less shear mixing of the injection jet with the mainstream and greater lateral spreading of the coolant compared to cylindrical holes. Haven et al [4] further proved that the diffuser shaped holes can reduce the strength of the anti-kidney pair of vortices which are harmful to the film coverage on the wall surface. Gritsch et al [5,6] investigated the film cooling performance of the same hole configurations as Thole et al [3].…”