Improved Methodologies for Time-Resolved Heat Transfer Measurements, Demonstrated on an Unshrouded Transonic Turbine Casing

The high pressure (HP) rotor tip and over-tip casing are often life-limiting features in the turbine stages of current gas turbine engines. This is due to the high thermal load and high temperature cycling at both low and high frequencies. In the last few years, there have been numerous studies of turbine tip heat transfer. Comparatively fewer studies have considered the over-tip casing heat transfer. This is in part, no doubt, due to the more onerous test facility requirements to validate computational simulations. Because the casing potential field is dominated by the passing rotor, to perform representative over-tip measurements a rotating experiment is an essential requirement. This paper details the measurements taken on the Oxford turbine research facility (OTRF), an engine-scale rotating turbine facility which replicates engine-representative conditions of Mach number, Reynolds number, and gas-to-wall temperature ratio. High density arrays of miniature thin-film heat-flux gauges were used with a spatial resolution of 0.8mm and temporal resolution of similar to 120 kHz. The small size of the gauges, the high frequency response, and the improved processing methods allowed very detailed measurements of the heat transfer in this region. Time-resolved measurements of TAW and Nu are presented for the casing region (-30% to +125% C-AX) and compared to other results in the literature. The results provide an almost unique data set for calibrating computational fluid dynamics (CFD) tools for heat transfer prediction in this highly unsteady environment dominated by the rotor over-tip flow.