Internal flow characteristics and performance evaluation of centripetal turbines in ocean thermal energy conversion

Ocean thermal energy, as a renewable and clean energy source, relies on a centripetal turbine as the core component of Ocean Thermal Energy Conversion (OTEC) system, which operate under low temperature differences, low flow rates, and compact design constraints. In this study, using R134a as the working fluid, the aerodynamic design and off-design performance of turbine were investigated through thermodynamic analysis, one-dimensional design, three-dimensional modeling, and multi-condition Computational Fluid Dynamics (CFD) simulations. The results demonstrate that under the design conditions (inlet mass flow rate (G) of 0.392 kg/s, inlet temperature (T0) 300 K, rotor speed (N) of 22,000 rpm), the turbine achieves an isentropic efficiency (ηs) of 77.9% and an output power (Pt) of 2.99 kW, with a well-structured internal flow field. Under a fixed geometric configuration, the performance is governed by the dynamic matching relationship among three operational parameters. G must be coordinated with N to avoid either underfilling or overload choking of flow passages, while T0 should be coupled with N, lower N favors lower T0 to maintain flow stability, whereas higher T0 benefits from elevated T0 to optimize internal energy conversion. Imbalance in the matching of parameters leads to deviations in velocity triangle, intensification of secondary flows, and a significant decline in efficiency. In practical operation, adjustments should be made within the vicinity of design conditions following the principle of synergistic matching among G, T0 and N, thereby achieving a unified balance of high efficiency, high power output, and high stability under the fixed structural constraints.