Flow Field Investigations on the Effect of Rib Placement in a Cooling Channel With Film-Cooling

Abstract

This paper presents experimental investigations on flat plate film-cooling in combination with a ribbed cooling channel. The effect of rib placement on the film-cooling injection and the flow in the cooling channel was studied. The velocity fields were measured using optical laser measurement techniques including LDA (laser doppler anemometry) and PIV (particle image velocimetry). A row of three cylindrical film holes is placed in the center rib segment of the cooling channel. The dimensionless rib-to-hole position s/D is varied from 4.5 to 10.5. The investigations are conducted at isothermal conditions for a variation of the coolant Reynolds number Rec,Dh from 10,000 up to 60,000 and for three blowing rates M = 0.5, 0.75, and 1.00. The flow field results for the film-cooling injection showed only a small influence of the rib placement. Due to different coolant-to-main flow pressure ratios across the row, a slight nonuniform share of coolant flow occurs. Intense streamwise mixing and decay of the turbulence in the film jet was observed within the first 10 hole diameters. Enhancement of the turbulence intensity inside the jet core was found with increasing coolant Reynolds numbers. Inside the internal cooling channel, the flow field showed significant influence of the rib position which is most pronounced at low Reynolds number (Rec,Dh = 10,000) and high blowing ratios (M = 1.0). The effect becomes significantly smaller when the Reynolds number is increased. This is mainly attributed to the strongly increasing channel mass flow which equals to a decreasing suction ratio SR = uh/uc of the holes. The experimental results are compared to comprehensive numerical simulations.