Heat transfer characteristics of a high-pressure turbine under combined distorted hot-streak and residual swirl: an unsteady computational study

Abstract

• Unsteady CFD simulations were performed for a transonic turbine stage to reveal the effects of uniform and swirled flows on hot-streak transport. • Two ideal hot-streak maps, radial and rounded, were evaluated against a realistic distorted hot-streak map. • The residual swirl contributed to the homogenisation of the radial hot-streak and the dispersion of the rounded and distorted hot-streaks through the rotor. • The distorted hot-streak showed the most complex transport behaviour through the stage. • The residual swirl was found to intensify the leakage vortex and increase the heat transfer rates near the tip region. In new generation aero-engines, lean-burn combustors are equipped with swirl injectors in order to reduce pollutant emissions. At the exit of these combustors, the flow is dominated by temperature non-uniformity (hot-streak) and residual swirl. Available research has focused mainly on the isolated effects of the residual swirl only or the hot-streak only on the aerodynamic performance or thermal performance of the high-pressure turbine (HPT). Only few studies investigated the combined swirl and hot-streak on the aerothermal performance of the HPT using either idealized uniform or rounded hot-streak topologies. Realistic hot-streaks generated from lean burn combustors have more complex topologies that involves distortions. The present study investigates the effects of residual swirl and distorted hot-streak simultaneously on a first stage of a HPT. Other hot-streak types, uniform and rounded, have been also investigated with and without swirl to perform comparisons with the distorted hot-streak. Unsteady Reynolds-averaged Navier–Stokes (URANS) computations have been conducted to assess the aerothermal performance of a HPT under the influence of different hot-streaks. Results revealed that all hot-streaks without swirl were almost preserved as transported through the vane and altered as transported through the rotor due to the secondary flows. Under the residual swirl, all hot-streaks were remarkably altered at the vane exit and deformed more at the rotor exit. The uniform hot-streak was homogenised through the rotor and the rounded and distorted hot-streaks were dispersed. The distorted hot-streak showed the most complex transport behaviour through the stage. Results also revealed that the leakage flow through the rotor tip gap generated high heat transfer rates, in particular on the rotor blade suction side and tip surface. The leakage flow formed the known leakage vortex at the tip gap exit, which induced high heat transfer rates. The residual swirl was found to intensify the leakage vortex and consequently higher heat transfer rates are generated compared to the uniform flow condition.