Trailing Edge Film Cooling of Gas Turbine Airfoils: External Cooling Performance of Various Internal Pin Fin Configurations

Abstract

The present paper describes an experimental study on trailing edge film cooling of modern high-pressure turbine blades using coolant ejection through planar slots on a pressure side cutback. The experimental test section consists of a generic scaled-up trailing edge model in an atmospheric open loop wind tunnel, which has been used in earlier studies by Martini et al. (e.g. [1]). An infrared thermographic measurement technique is employed, which allows for the application of engine-realistic density ratios around 1.6 by increasing the main flow temperature. The effects of different geometric configurations on the structure and performance of the cooling film are investigated in terms of film cooling effectiveness, heat transfer, and discharge behavior. Among other issues, the interaction between internal turbulators, namely an array of pin fins, with the ejection slot lip is of major interest. Therefore, different designs of the coolant ejection lip are studied. Four different ratios of lip thickness to ejection slot height (t/H = 0.2, 0.5, 1.0, 1.5) are investigated as well as three different lip profiles representing typical manufacturing imperfections and wear. Other geometric variations comprise elliptic pin fins with spanwise and streamwise orientation and the application of land extensions from the internal coolant cavity onto the cut-back surface. The blowing ratio is varied between 0.2 < M < 1.25. In terms of film cooling effectiveness the results show a strong dependency on ejection lip thickness and minor improvements are obtained with a rounded ejection lip profile. Significant improvements are achieved using land extensions. The elliptic pin fins have a strong effect on discharge behavior as well as on film cooling effectiveness and heat transfer. Except for the elliptic pin fins, the geometric variations have only a minor influence on heat transfer.