Experimental Investigations on Aero-Thermal Interaction of Film Cooling Air Ejected From Multiple Shallow Angle Cooling Holes: Effect of Freestream Turbulence

The objective of the present study is to investigate the aero-thermal interaction of the secondary air injected from multiple shallow angled film cooling holes. The focus is on the influence of freestream turbulence on the film cooling effectiveness and secondary flow field. For the experiments, infrared thermography and Laser Doppler Velocimetry (LDV) were employed. The experiments were conducted at a Reynolds number based on the hole diameter, Re_D = 6200 at blowing ratio, BR = 1.0 and 2.0. Two flat plate test models; TMA and TMG, have been considered, which involved twenty cylindrical holes constituting a matrix composed of four rows with five holes in each row. The cooling holes for both test models were inclined at 20° in the streamwise direction with the lateral pitch, P_z = 6D for TMA and 3D for TMG. Two different freestream turbulence levels have been considered for both the aerodynamic and thermal investigations. The results of LDV show two distinct dynamics for each test model which influence the flow field differently. Consequently, the thermal field produced a distinctive film cooling effectiveness distribution of each test model. Higher freestream turbulence level enhances the mixing in the vicinity of the vortical structure thus deterring the film cooling effectiveness just downstream of the cooling hole but aids to lateral spreading of the coolant further downstream of the cooling hole, providing greater film effectiveness coverage.