A Combined LES and PIV Investigation of Trenched Fan-Shaped Hole Aerodynamics

Trenches implemented in the thermal barrier coating have been proved to be a feasible solution to increase the thermal performance of film cooling holes. The performance of this solution can be maximized by properly selecting the trench design. The present paper reports the results of a combined experimental and numerical investigation carried out on a flat plate model with a set of three 7-7-7 fan-shaped holes. The Particle Image Velocimetry (PIV) technique was used to measure the in-plane mean and fluctuating velocity components in the trench region on the mid-hole section for variable injection conditions corresponding to various coolant to mainstream blowing ratios M in the range between 0.5 and 2.0. Cases at a momentum flux ratio I = 1.5 were used to cross check the prediction capability of a Large Eddy numerical simulation (LES) for two trench geometries previously thermally tested. PIV and LES result to be in good agreement. Both contribute to the understanding of the complex aerodynamics taking place inside the trench, supporting the thermal analysis. In particular, the presence of a vortical structure in the cavity downstream corner in the mid-hole section and the absence of counter-rotating vortex pair are the main reasons for the better performance of the deeper and shorter trench (Case#2).