The Effects of Biot Number on the Conjugate Film Cooling Effectiveness Under Different Blowing Ratios

Abstract

Based on the one-dimensional heat transfer analysis of film cooled turbine blade, the correlation between overall cooling effectiveness and Biot number was obtained, where Biot number represents the ratio of the solid thermal resistance to the external convective heat transfer resistance. And a new parameter — net film cooling effectiveness was defined to evaluate the film cooling performance in the case of conjugate film cooling. Conjugate heat transfer simulation was carried out by using the commercial CFD package CFX for the typical cylindrical film cooling holes on flat plate. The influences of Biot number under different blowing ratios on laterally-averaged overall film cooling effectiveness, laterally-averaged and area-averaged net film cooling effectiveness were investigated systematically. The results showed that due to the effect of solid heat conduction, laterally averaged overall film cooling effectiveness is higher than adiabatic film cooling effectiveness, and the upstream region of the cooling hole can also be cooled by the coolant. With the decrease of Biot number, both the stream-wise and laterally overall cooling effectiveness are more uniform, and laterally-averaged net film cooling effectiveness is reduced. The trend of laterally-averaged net cooling effectiveness under different blowing ratios is consistent with the adiabatic case, but has lower values. For the engine-like Biot number Bi = 0.36, compared with the low blowing ratio M = 0.5 case, the value of area-averaged net film cooling effectiveness is reduced about 29% and 65% correspondingly under blowing ratio M = 1.0 and M = 1.5.