Large eddy simulation of single and multi-holes of film cooling

In this research, numerical studies have been performed by Reynolds averaged Navier Stokes (RANS) and large eddy simulations (LES) to investigate the effect of a novel film cooling design multi-holes on the film cooling effectiveness over a flat surface. A single cylindrical hole with 11.1 mm diameter and multi-holes (14 holes with a diameter of 2.97 mm) with fan configuration are considered for simulations. Numerical simulations are performed at a fixed density ratio of 1.6, length-to-diameter of 4, an inclined angle of 35o and blowing ratio 1.25. The results of the present study show that replacing a single hole with multi-holes results in a considerable increase in film cooling effectiveness in both axial and lateral directions, so that leads to an increase of about 94 percent in the area-averaged film cooling effectiveness. In the fan-shaped configuration, the scale of hairpin vortices is smaller than the single cylindrical hole, and forming of the vortices occurs in farther regions downstream of the hole. A pair of anti-jet vortices is formed in the structure of the multi-holes and the rotation direction of these vortices is opposite to the CRVP direction.