The Influence of Turbine Clearance Gap Leakage on Passage Velocity and Heat Transfer Near Blade Tips: Part I—Sink Flow Effects on Blade Pressure Side

Abstract

A study has been conducted to investigate influences of tip leakage flow on heat transfer and flow development along the pressure side of a gas turbine blade. An analysis of the sink character of the flow situation indicates that high velocities and accelerations are generated very near the gap, and an apparatus was specifically designed to model the phenomena and to permit resolution of the expected localized near-gap heat transfer enhancement. In the experiments, leakage flow was drawn from an adjustable stream wise corner slot in a straight square test channel. A thin stainless steel ohmic-heated test surface adjacent to the slot simulated the airfoil surface. Supporting nonintrusive mean and fluctuating flowfield measurements were conducted with a laser-Doppler anemometer to aid interpretation of the heat transfer results and to provide a basis for comparison with future numerical predictions. The flowfield measurements confirm that near the gap the flow is highly accelerated, and indicate apparent relaminarization of the initially turbulent boundary layer. The heat transfer measurements show that leakage generates large increases in local heating near the gap. The presence of this undesirable enhancement helps to explain observed in-service material distress and failures of blades that appear to initiate at the pressure side tip.