Effect of rib orientation on film cooling performance

Based on the smooth secondary flow crossflow channel case, two ribbed channels (135° ribs and 45° ribs) were compared to find out the orientation effect on film cooling performances. The heat transfer coefficient ratio and local film cooling effectiveness were measured by a transient liquid crystal technique. Reynolds averaged Navier Stokes (RANS) simulations with realizable k-ε turbulence model and enhanced wall treatment were performed using a commercial code Fluent. In the smooth secondary flow channel case, a helical motion of secondary flow was observed in the film hole, and this motion induced strong velocity separation and flow loss. The cooling air jet was divided into two parts, one consisting of a pair of skewed vortices. In the 135° ribs case, the vortex in the upper half region of the secondary flow channel rotates clockwise, inducing the coolant much easier to flow into the film hole, and straight stream lines in film hole are observed in this case. In the 45° ribs case, the vortex close to the film hole rotates counter clockwise, which enhances the vortices in the film hole. Flowing into the film hole, the flow structure of the coolant in the 45° ribs case is similar with the smooth crossflow channel case. The highest film cooling effectiveness and lowest heat transfer coefficient ratio is observed in the 135° ribs case.