HEAT TRANSFER AND ADIABATIC FILM COOLING EFFECTIVENESS ON HIGHLY LOADED HIGH PRESSURE TURBINE BLADES WITH FLOW SEPARATION

摘要

Film cooling experiments were run at the High-Speed Cascade Wind-Tunnel of the University of the Federal Armed Forces Munich. The investigations were carried out on a linear cascade of aerodynamically highly loaded turbine blades. The main targets of the tests were to assess the film cooling effectiveness and the heat transfer in zones with main flow separation. The cascade was designed to have a large zone with flow separation on the pressure side starting at the leading edge and reaching up to approximately half of the axial chord. Film cooling is provided on the pressure side at the front part of the blade in order to reduce flow separation and to provide effective film cooling inside the separation bubble and at the reattachment zone. The studies comprise the measurement of adiabatic film cooling effectiveness and heat transfer coefficient for the different cascades under a set of different Mach and Reynolds numbers at engine relevant levels. Periodic wakes, generated by bars moving upstream of the cascade, simulate the rotor stator interaction. The results show that film cooling is detrimental for cooling the surface inside the flow separation zone, whereas after reattachment improved overall film cooling effectiveness is obtained with periodic unsteady inflow compared to the cases with homogeneous inflow.