Effects of Periodic Unsteady Inflow on Film Cooling and Heat Transfer on Highly Loaded High Pressure Turbine Blades With Flow Separation

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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 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 previous 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. This cascade was changed for a new design with a larger pitch to chord ratio in order to set the focus on flow separation on the suction side. This increased pitch forces a massive separation on the suction side due to strong shocks. The flow separation is controlled with aid of vortex generating jets in order to reduce the total pressure loss caused by it. Film cooling is provided on the suction side upstream of the vortex generating jets. The measurements comprise of blade loading, profile loss, adiabatic film cooling effectiveness, and heat transfer coefficient under two Mach numbers at a Reynolds number of 390,000. In a previous publication detailed results with homogeneous inflow where shown. Now, the focus is set on the effects of periodic unsteady wakes resulting from bars moving upstream of the cascade. These moving bars create a periodic unsteady inflow similar to the interaction between stator and rotor in the machine. It is shown how these wakes have significant influence on the heat transfer in the acceleration region of the suction side and affect the adiabatic film cooling effectiveness upstream of the shock.