Numerical investigation of film cooling performance with different internal flow structures

Four coolant channel configurations, including supply plenum without crossflow, smooth channel with crossflow and ribbed channels with crossflow ( 135° and 45° angled ribs), are simulated to find out the effect of internal flow structures on the external film cooling performance. Reynolds Averaged Navier Stokes (RANS) simulations with realizable k-ε turbulence model and enhanced wall treatment are performed using a commercial code Fluent. Blowing ratios cover a range from 0.5 to 2.0. For the three cases with crossflow, a constant Reynolds number, Re_Dh, is fixed as 100000. Particular attention has been paid to the flow structures and counter-rotating vortices. Helical motion of secondary flow is observed in the hole of the smooth case and the 45° ribs case, inducing strong velocity separation in the cooling hole and blocks at the entrance and exit. In the two cases, the cooling-air jet divides into two parts after being blown out of the hole and a pair of skewed vortices appears downstream. In the 135°ribs case, the vortex in the upper half region of the secondary flow channel rotates in the same direction with the hole inclination direction, the straight stream lines are generated and therefore lower loss and higher discharge coefficient. Experimental data of the smooth case and the 135° ribs case show the good agreement with the numerical results.