Effect of Straight and Compound Blade Lean on the Aerodynamic Performance of a High-Pressure Turbine Nozzle Guide Vane under Residual Swirl

Abstract

The exhaust flow at the outlet of modern lean-burn combustors, which offer reduced NOx emissions for gas turbines, is characterized by hot streaks (HS) and residual swirl that affect the aerothermal performance of downstream high-pressure (HP) turbine nozzle guide vanes (NGVs). Although leaned blades are widely employed in turbomachinery design to mitigate secondary flow losses and improve aerodynamic efficiency, the combined influence of straight and compound lean configurations under residual swirl conditions remains comparatively less investigated. The objective of this study is therefore to numerically investigate the effect of blade lean on secondary flows and aerodynamic losses in axial turbine NGVs operating under simplified combustor-exit swirl conditions. The investigations are conducted on the NGV annular cascade developed at the NASA Lewis Research Center. Steady compressible flow simulations are performed by solving the Reynolds-Averaged Navier–Stokes equations using the Shear Stress Transport turbulence model. Three-dimensional vane geometries are generated by stacking the 2D blade profile along linear positive and negative lean axes with respect to the radial direction, with lean angles ranging from α = −8° to +8°. A total of sixteen configurations are first analyzed under axial inflow conditions to evaluate the influence of blade lean on aerodynamic performance. Based on the obtained performance trends, the baseline configuration together with the optimum straight-lean and compound-lean cases are subsequently investigated under two inlet swirl orientations (positive and negative) applied at the leading edge, with a swirl intensity of |Sn| = 0.4.The results show that the negative straight lean configuration NSL02 reduces the total pressure loss coefficient by approximately 3% under axial inflow conditions and by about 14% under negative swirl compared with the baseline case. Under positive swirl conditions, the negative compound lean configuration NCL08 achieves the best performance, reducing the loss coefficient from 2.274 to 1.914, corresponding to an improvement of approximately 16%.