Numerical Design of Experiments for Repeating Low-Pressure Turbine Stages Part 2: Effect of Reynolds Number on Different Blade Geometries

The complex transitional and turbulent nature of unsteady flows seen in Low-Pressure Turbines (LPTs) often demands high-order methods such as Large Eddy Simulations (LES) for accurate predictions of turbine efficiency and loss generation. This study presents results from a highly resolved LES and state-of-the art Unsteady Reynolds-Averaged Navier-Stokes (URANS) database for three newly designed LPT profiles. These are a conventional standard lift profile, a front-loaded high-lift profile, and an aft-loaded profile. Each profile is evaluated individually within a repeating 1.5-stage LPT configuration operating under engine-like conditions at an isentropic exit Mach number of 0.3. A Reynolds number sweep, ranging from 70,000 to 320,000, captures a broad spectrum of engine-relevant flow conditions. The LES study incorporates time-resolved, time-averaged, and phase-locked averaged results, enabling a detailed examination of unsteady flow phenomena such as blade-wake interactions, unsteady boundary layer evolution, and loss generation mechanisms. Complementary URANS calculations of the same configurations are undertaken and compared with the LES data. While trends are largely recovered, important differences with the LES data can be identified. These are especially present for the aft-loaded profile, it being a radical blade design compared to conventional profiles, highlighting the necessity for turbulence and transition modelling improvements when considering more aggressive blade designs. Ultimately, this work advances the understanding of unsteady aerodynamic phenomena in LPTs via LES and lays the foundation for the development of more accurate URANS models.