Effects of a Wake on Turbine Blade Heat Transfer in a Transonic Cascade

Abstract

The effects of a wake generated by a stationary upstream strut on surface beat transfer to turbine blades were measured experimentally in a heated, transonic cascade tunnel. Five pitchwise locations of the upstream strut were tested, while maintaining a constant axial distance between the strut and the leading edge plane of the cascade. Time-resolved unsteady heat flux measurements were made with Heat Flux Microsensors (HFM) at three positions on the suction surface and one position on the pressure surface. In addition, hot-wire surveys were taken along the leading edge plane of the cascade to document the disturbance generated by the upstream strut. Results from the hot-wire surveys show that with the strut placed upstream and near the stagnation point of the turbine blade, the turbulence intensity in the wake was as high as 50%. This high level of turbulence intensity was due to the coupling of the strut wake with the potential flow around the blunt leading edge of the turbine blade. A strong influence on the heat transfer coefficient was seen from the relative pitchwise position of the strut with respect to the leading edge of the test blades. For the suction surface, the maximum increase in average heat transfer coefficient occurred when the upstream strut was placed near the stagnation point of the blade. The heat transfer coefficients were increased by 15, 20, and 10% for the gages located on 10, 22, and 50% chord positions of the suction surface, respectively, compared to the baseline case of no strut. For the pressure side, results show the maximum increase in heat transfer coefficient occurred when the upstream strut was placed along the pitchline near the middle of the blade passage. At 30% chord position on the pressure surface, the heat transfer coefficient was increased by 25 %. Attempts to correlate these increases in mean heat transfer with integral values of the measured unsteadiness of the flow or heat flux were not successful.