Effect of a Combined Hot-Streak and Swirl Profile on Cooled 1.5-Stage Turbine Aerodynamics: An Experimental and Computational Study

Abstract

Recently developed lean-burn combustors offer reduced NOx emissions for gas turbines. The flow at exit of lean-burn combustors is dominated by hot streaks and residual swirl, which have been shown—individually—to impact turbine aerodynamic performance. Studies have shown that residual swirl at inlet to the high-pressure (HP) stage predominantly affects the vane aerodynamics, while hot streaks affect the rotor aerodynamics. Studies have also shown that these changes to the HP stage aerodynamics can affect the downstream intermediate-pressure (IP) vane aerodynamics. Yet, to date, there have been no published studies presenting experimental turbine test data with both swirl and hot streaks simultaneously present at inlet. This paper presents the first experimental and computational investigation into the effects of combined hot streaks and swirl on turbine aerodynamics. Experimental measurements were conducted in the Oxford Turbine Research Facility (OTRF), a short-duration rotating transonic facility, in which the nondimensional parameters relevant to turbine fluid mechanics and heat transfer are matched to engine conditions. The turbine under investigation is the recently commissioned LEMCOTEC turbine, which has been designed to represent modern aero-engine architectures and for robustness to lean-burn combustor-representative inlet flows. The turbine comprises an unshrouded HP stage with fully film-cooled vanes followed by low-turning IP vanes in an S-shaped duct. Two turbine inlet flows are considered. The first is uniform in total pressure, total temperature, and flow angle. The second features a nonuniform total temperature (hot streak) profile featuring strong radial and weak circumferential variation superimposed on a swirling velocity profile. This combined nonuniform profile is generated using a new combustor simulator that has recently been commissioned in the OTRF. Detailed area surveys of the flow were conducted at turbine inlet, HP rotor exit, and IP vane exit, and loading distributions were measured on the HP and IP vanes. Measurements and unsteady Reynolds-averaged Navier–Stokes (URANS) predictions suggest that the inlet temperature nonuniformity was relatively well preserved upon being convected through the turbine: the predicted root-mean-square variation in the IP vane exit total temperature field was approximately double that with uniform inlet conditions. Relatively poor comparisons between URANS and experiment highlight the challenge of accurately predicting the complex IP vane flow. In particular, small differences in exit whirl angle resulted in substantial differences in IP vane exit velocity and thus radial pressure gradient.