Optimization of trailing edge ejection mixing losses: A theoretical and experimental study

The aerodynamic effects of trailing edge ejection on mixing losses downstre am of cooled gas turbine blades were experimentally investigated mid compar ed with an already existing one-dimensional theory by Schobeiri (1989). The significant parameters determining the mixing losses and, therefore, the e fficiency of cooled blades, are the ejection velocity ratio, the cooling ma ss flow ratio, the temperature ratio, the slot thickness ratio, and the eje ction flow angle. To cover a broad range of representative turbine blade ge ometry and flow deflections, a General Electric power generation gas turbin e blade with a high flow deflection and a NASA-turbine blade with intermedi ate flow deflection and different thickness distributions were experimental ly investigated and compared with the existing theory. Comprehensive experi mental investigations show that for the ejection velocity ratio mu = I, the trailing edge ejection reduces the mixing losses downstream of the cooled gas turbine blade to a minimum, which is in agreement with the theory. For the given cooling mass flow ratios that are dictated by the heat transfer r equirements, optimum slot thickness to trailing Edge thickness ratios are f ound which correspond to the minimum mixing loss coefficients. The results allow the turbine aerodynamicist to minimize the mixing losses and to incre ase the efficiency of cooled gas turbine blades.