Investigation on overall performance of double-jet film cooling holes with various spanwise distance

The overall film cooling performances of double-jet film cooling (DJFC) holes on a flat plate were evaluated experimentally and numerically including the film cooling effectiveness (eta), heat transfer coefficient (HTC) ratio, as well as the net heat flux reduction (NHFR) parameter. The spanwise distance (p/d) varied as 0.5, 1.0, 1.5, and the streamwise distance (s/d) was kept as 3.0. Results show that p/d = 0.5 has the highest cooling effectiveness and the highest net heat flux reduction parameter among all configurations. When the blowing ratio is low, all the DJFC configurations have high film cooling effectiveness and positive NHFR values. However, the NHFR becomes negative for the cases of p/d = 1.0, 1.5 at high blowing ratios, which means the increased heat flux is larger than the case without film cooling. From the flow field, film effectiveness distribution is largely affected by the anti-kidney vortex which is relevant to p/d and blowing ratios (M). The heat transfer coefficient ratio profile is mainly connected to the turbulent kinetic energy (TKE) enhanced by the jet interaction.