Optimization of Endwall Ridging for Enhanced Efficiency in Aggressive Turbine Vaned Ducts

This study presents a joint experimental and numerical investigation on the impact of endwall ridging on the efficiency of a turbine nozzle guide vane (NGV). Experiments are conducted on a large-scale, low aspect ratio cascade replicating a high-diffusion stage between the high-pressure turbine (HPT) and the low-pressure turbine (LPT). The cascade is tested in its baseline configuration and with two endwall ridging devices, one of which is optimized through parametric computational fluid dynamics (CFD) simulations by varying ridge height, spacing, and position within the blade channel. A Pareto front analysis identifies the optimal configuration that maximizes flow uniformity at the cascade exit while minimizing losses. The flow field is experimentally investigated in a radial-tangential plane at the cascade exit using a five-hole probe to assess total pressure losses and flow angle uniformity, key factors for evaluating carry-over effects on the downstream row and refining CFD predictions. Additionally, CFD streamline visualizations provide further insight into the ridging device operation. The findings demonstrate that the optimized endwall ridging effectively mitigates the cross-stream flow induced by the passage vortex. As a result, flow uniformity is enhanced, leading to increased cascade efficiency compared to the baseline configuration.