Effect of aggressive inlet swirl on heat transfer and aerodynamics in an unshrouded transonic HP turbine

Swirling flows are now widely being used in modern gas turbine combustors to improve the combustion characteristics, flame stability, and reduce emissions. Residual swirl at the combustor exit will affect the performance of the downstream high-pressure (HP) turbine. In order to perform a detailed investigation of the effect of swirl on a full-scale HP turbine stage, a combustor swirl simulator has been designed and commissioned in the Oxford Turbine Research Facility (OTRF), previously located at QinetiQ, Farnborough UK, as the Turbine Test Facility (TTF). The swirl simulator is capable of generating engine-representative combustor exit swirl distributions at the turbine inlet, with yaw and pitch angles of up to 40 deg. The turbine test facility is an engine scale, short duration, rotating transonic turbine facility, which simulates the engine representative M, Re, Tu, nondimensional speed, and gas-to-wall temperature ratio at the turbine inlet. The test turbine is a highly loaded unshrouded design (the MT1 turbine). This paper presents time-averaged experimental heat transfer measurements performed on the rotor casing surface, and on the rotor blade surface at 10%, 50%, and 90% span. Time-averaged rotor casing static pressure measurements are also presented. Experimental measurements with and without inlet swirl are compared. The measurements are discussed with the aid of three-dimensional steady and unsteady CFD simulations of the turbine stage. Numerical simulations were conducted using the Rolls-Royce in-house code HYDRA, with and without inlet swirl.