Effect of Film-Hole Shape on Turbine-Blade Heat-Transfer Coefficient Distribution

Abstract

Detailed heat-transfer coefe cient distributions on the suction side of a gas turbine blade were measured using a transient liquid crystal image method. The blade has only one row of e lm holes near the gill-hole portion on the suction side of the blade. Studies on three different kinds of e lm-cooling hole shapes were presented. The hole geometriesstudied includestandard cylindricalholesand holeswith adiffuser-shaped exitportion (i.e., fan-shaped holes and laidback fan-shaped holes ). Tests were performed on a e ve-blade linear cascade in a low-speed wind tunnel. The mainstream Reynolds number based on the cascade exit velocity was 5 :3 ££ 10 5 . Upstream unsteady wakes were simulated using a spoke-wheel-type wake generator. The wake Strouhal number was kept at 0 and 0.1. The coolant-to-mainstream blowing ratio was varied from 0.4 to 1.2. The results show that unsteady wake generally tends to induce earlier boundary-layer transition and enhance the surface heat-transfer coefe cients. When compared to the cylindrical hole case, both the expanded hole injections have much lower heat-transfer coefe cients over the surface downstream of the injection location, particularly at high blowing ratios. However, the expanded hole injections induce earlier boundary-layer transition to turbulence and enhance heat-transfer coefe cients at the latter part of the blade suction surface.