Film Cooling Effectiveness Enhancement Applying another Jet in the Upstream Neighbor of the Main Jet-Using LES Approach

Flow hydrodynamic effects and film cooling effectiveness of placing a coolant port (upstream jet) just upstream of the main cooling jet were numerically investigated. The upstream jet was added such that the total cooling cross section (cross sections of the main and upstream jets) remains constant, in comparison to the case of ordinary cooling jet. The finite volume method and the unsteady SIMPLE algorithm on a multiblock non-uniform staggered grid arrangement were applied. The large eddy simulation (LES) approach with the one equation subgrid scale model was used. The jet to cross flow velocity ratio (for both of the main and the upstream jets) is 0.5 and the cross flow Reynolds number (based on the main jet parameters) is equal to 4700. The obtained results showed a significant improvement in the flow control capability and both centerline and span-wise averaged film cooling effectiveness applying the new cooling configuration. Effects of the upstream jet dimensions are also studied here. The obtained results showed that the span-wise width of the upstream jet has more essential influence on the cooling performance than that of its stream-wise width. Moreover, it is demonstrated that the film cooling performance could be enhanced even by applying an upstream jet which its temperature is as same as the cross-flow temperature, i.e. applying a hot upstream jet. Finally, it is shown that presence of the upstream jet decreases the stream-wise component of the velocity near the wall, which decreases the wall shear stress and the skin friction drag coefficient significantly.