Experimental Investigation of the Effects of Blowing Ratio Parameter on HeatTransfer to a Film-Cooled Flat Plate

摘要

The effects of blowing ratio on film cooling effectiveness were investigated. Tworound-nosed test plates were used. One made of aluminum and the second of corian (low thermal conductivity). Injection at 35 degrees in the downstream direction was studied. Helium was mixed with air to produce a density ratio (coolant to mainstream) of 1.6 and 2.0, while the blowing ratio varied from 0.3 to 2.2. Surface temperature was measured by thin film gages located up to a nondimensional downstream distance X/D of 30. Two injection regimes, weak and strong, were found. In the weak regime, film cooling reduced gage heat flux at all thin film gage locations, however, film cooling was more effective for X/D < 10. In the strong regime, the effectiveness of film cooling for X/D < 10 was greatly reduced. Maximum film cooling effectiveness occurred between the weak and strong regime at a blowing ratio of 1.0. Changing the density ratio from 1.6 to 2.0 varied the measured gage heat flux less than 5 percent. Gage heat flux was correlated by the velocity ratio scaling parameter (X/D)VR to the -4/3 in both injection regimes. Gage heat flux with no film cooling, assuming a turbulence level of 10 percent, deviated less than 8 percent from theoretical results using the corian plate, and less than 10 percent using the aluminum plate.... Film cooling, Heat transfer, Shock tube, Turbulent flow, Density ratio, Blowing ratio, Flat plate, Gas turbine.