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 nonuniform 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 spanwise 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 spanwise width of;the upstream jet has more essential influence on the cooling performance than that of its streamwise 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 crossflow temperature, i.e. applying a hot upstream jet.;finally, it is shown that presence of the upstream jet decreases the streamwise component of the velocity;near the wall, which decreases the wall shear stress and the skin friction drag coefficient significantly.