Numerical and Experimental Studies of Transpiration Cooling Film Effectiveness Over Porous Materials

摘要

Comprehensive experimental and numerical studies were performed to determine cooling film effectiveness (CFE) of transpiration cooling over porous materials. The CFE was evaluated experimentally using pressure sensitive paint (PSP) by invoking heat/mass transfer analogy over the surface of the porous samples. It was found that transpiration cooling can reduce total surface heat flux by two to three times and provide solid surface CFE on average 15% to 30% higher than multi-hole effusion cooling. The numerical model allowed detailed investigation of the flow evolution in the porous media and its ability to create a uniform thermal protection film. Modeling results revealed the flow inside the porous media moves slightly laterally, in the same direction as the main flow due to the viscous effect of the channel flow and low flow resistance provided by the porous samples. This effect causes a large amount of coolant to exit at the trailing edge of the porous media, creating a nonuniform cooling film protection. The model also demonstrates that CFE is dependent on the physical properties (permeability and inertial coefficient) of the porous media. The study indicates that increasing the coolant flow rate increases film protection and that the pore size in the range of 10 to 40 pores per inch does not have a significant effect on the film protection.