High Resolution Heat Transfer Measurement Technique on Contoured Endwall With Non-Uniform Thermal Resistance

Abstract

The introduction of endwall contouring in the design of modern gas turbines has helped to improve the aerodynamic performance. In fact, the management of secondary flows and the control of purge air flow are limiting the generation of losses and enhancing the use of coolant air. The impact of such geometrical features on the endwall thermal loads is then of primary interest for designers in charge of optimizing the cooling of the components and ensuring their mechanical integrity. This paper focuses on heat transfer measurement on a contoured vane endwall installed in an axial turbine. The measurements were performed on a dedicated platform installed in the axial turbine rig of ETH Zurich, using a quasi-isothermal boundary condition and an infrared camera traversed by a multi-axis robot-arm. Due to the complex geometry, a mis-attachment of the insulating Kapton layer was observed in several regions of the passage and corrupted the measurements of about 20% of the endwall. An experimental correction method based on the surface response to laser step heating was developed. A specific setup was constructed and used to map the surface response of a calibration plate with flat bottom holes and the heat transfer platform. A model linking the response to the bubble thickness was obtained and used to successfully correct the results. The heat transfer data were obtained for two turbine operating conditions at ReCax = 720000 and 520000. The correction technique, commonly used for defects detection, has been applied in a quantitative manner to provide successful correction of the measurements for different operating conditions.