Aerodynamic Design and Optimization of a Radial Inflow Turbine for Organic Rankine Cycle Systems with Physics-Guided Flow Diagnostics
Improving the performance of radial inflow turbines under coupled aerodynamic and mechanical constraints remains a key challenge in high-speed Organic Rankine Cycle (ORC) systems. In magnetically supported configurations, turbine design is restricted by axial thrust limitations, while maintaining the target mass flow rate is essential for stable system operation. To address these challenges, this study develops a physics-guided design approach for a high-speed ORC radial inflow turbine by integrating one-dimensional preliminary design, three-dimensional CFD-based optimization, and enthalpy gradient magnitude (EGM)-based flow diagnostics. The numerical model is validated against experimental data of a baseline turbine. Three key geometric parameters are optimized under coupled axial thrust and mass flow constraints. The optimized design increases the total-to-total isentropic efficiency from 74.7% to 87.1% while maintaining acceptable axial loading. EGM analysis shows that high-efficiency configurations exhibit more uniform spatial distributions of energy gradients within the impeller passages, whereas low-efficiency cases are characterized by localized high-gradient regions associated with flow separation and secondary flow structures. A volumetric average EGM parameter is further introduced for quantitative evaluation and exhibits a clear negative correlation with turbine efficiency. The optimized efficiency reported herein is a numerical prediction requiring future experimental validation. The results demonstrate that improved internal flow organization contributes significantly to turbine performance enhancement and provides diagnostic insights for design evaluation of high-speed ORC turbines.