Density Ratio Effects on the Flow Field Emanating From Cylindrical Effusion and Trenched Film Cooling Holes
The present paper investigates density ratio effects on the flow field of cylindrical hole effusion and trench film cooling. An extensive parametric study of varying blowing rates (M = 1; 2; 4; 6), momentum (I = 1; 2; 8; 16) and velocity ratios (VR = 0.5; 1; 2) was carried out at three different density ratios (DR = 1.33; 1.6; 2). All cases were simulated using the realizable k-ε turbulence model with enhanced wall treatment. The mainstream boundary conditions were kept constant, while the coolant mass flow and temperature were varied. Additional 2D PIV measurements in streamwise planes and planes parallel to the wall were carried out in a heated, closed loop wind tunnel with an injection of cryogenically cooled air. For constant momentum ratios, the jet core trajectories for both configurations were almost independent from the density ratio. In case of a constant blowing ratio, the jet penetration decreased with the density ratio, while it increased for a constant velocity ratio. Downstream of the trench a large recirculation zone is visible. Furthermore, cooling air is forced out of the trench in the midplane between two cooling holes.