FIND Parallel: A parallel numerical solver for large-scale simulations of cross-scale spiral-wound reverse osmosis...

Concentration polarization (CP) and pressure drop significantly impact reverse osmosis (RO) efficiency. While prevailing computational fluid dynamics (CFD) studies often rely on periodic unit-cell models, these approaches may not fully capture the cumulative development of transport phenomena along the channel. To explore this, we developed a high-fidelity, long-domain CFD framework (350 million cells) to simulate engineering-scale channels. Our findings suggest that the conventional flat-plate idealization can introduce modeling deviations: simplified 90°corners may elevate the predicted Sherwood number via localized stagnation-driven mixing, while concentrated viscous dissipation can affect the estimation of hydraulic resistance. In contrast, semi-cylindrical spacers, which more closely resemble actual extruded filaments, help mitigate these numerical artifacts by facilitating a curvature-driven, spatially distributed momentum exchange. This mechanism shift corresponds to a 3.1% reduction in friction factor (f: 4.16 to 4.03), offering a refined perspective on pumping requirements. Furthermore, the semi-cylindrical geometry minimizes stagnation zones, potentially reducing a common driver of localized fouling. Ultimately, this study highlights how geometric fidelity influences the interpretation of RO hydrodynamics, suggesting the semi-cylindrical model as a highly representative baseline for engineering-scale predictions.