Effect of film-hole shape on turbine-blade heat-transfer coefficient distribution
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Detailed heat transfer coefficient distributions on the suction side of a gas turbine blade were measuredu sing a transientl iquid crystal imagem ethod. The blade has onIy one row of film holes near the gill hole portion on the suction side of the blade. Studies on three different kinds of film cooling hole shapes were presented. The hole geometries studied include standard cylindrical holes and holes with a diffusershaped exit portion (i.e., fanshaped holes and laidback fanshapedh oles). Tests were performedo n a five-blade linear cascade in a low-speed wind tunnel. The mainstream Reynolds number based on the cascade exit velocity was 5.3105. 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-mainstreamb lowing 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 coefficients. When compared to the cylindrical hole case, both the expanded hole injections have much lower heat transfer coefficients 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 coefficients at the latter part of the blade suction surface. 2000 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
