An experimental test rig is constructed to study the effect of pressure gradient on different configurations of the anti-vortex film cooling technique. This technique depends on adding a pair of cylindrical anti-vortex holes branching out from the main cylindrical film cooling holes to mitigate the effect of kidney vortices that causes the jet to lift off. Four different values of velocity ratios (VR), (Coolant Jet Velocity/Main Stream Velocity) namely VR=0.5, 1.0, 1.5, and 2.0, are studied with three different positions of anti-vortex holes. A single row of 30o angled holes on a flat surface, under zero pressure gradient along the downstream test surface, is taken as a baseline case. The numerical study is carried out using FLUENT commercial code using the k-ε model. The density ratio is taken in consideration. Numerical results are first compared with experimental values of temperatures and film cooling effectiveness and the comparisons verified the numerical model. Both of experimental and numerical studies show that the new technique improves the film cooling effectiveness.
The numerical velocity vectors in the boundary layer region showed that the anti-vortex holes create reverse vortices against the main vortices that are created by the main hole. These reverse vortices help in keeping the coolant jet flow near the surface. The adverse pressure gradient decreases the film cooling effectiveness while the presence of favorable pressure gradient increases the film cooling effectiveness.