On the Impact of Upstream Bump Geometry on the Aerothermal Performance of a 7-7-7 Shaped Hole

A way to increase film cooling effectiveness levels downstream of film cooling holes is through a modification in the surface morphology upstream of the hole. The presence of a bump in front of the hole, if properly sized, can reduce the jet to mainstream interaction, resulting in a laterally uniform coolant layer. The performance of this solution depends on the bump geometrical characteristics, namely its height and width, and on the distance from the hole. The present paper reports the results of a combined thermal and aerodynamic experimental investigation carried out on a flat plate model with a set of three fan-shaped holes. PSP and PIV techniques were used to characterize the flow behavior and the adiabatic film cooling effectiveness of the standard shaped hole case and of two bump configurations coming from a Reynolds Averaged Navier-Stokes (RANS) based optimization procedure. The aero-thermal performance has been examined at different coolant to mainstream blowing ratios M in the range between 0.5 and 2.0. Experimental data are complemented with Large Eddy Simulation (LES) results, allowing a fully assessment of the performance of the bump when applied to fan-shaped holes. Numerical simulations and experiments related the improvement and the penalty in thermal protection to the nature of interaction of separated boundary layer downstream the bump and the coolant at different freestream velocity and coolant injection jet-conditions.