An experimental test rig is constructed to study
different configurations of the film cooling technique
developed at NASA Glenn Research Center. 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, which
gives a zero pressure gradient along the downstream test
surface, is taken as a baseline. The different holes
configurations are tested. 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. |
