Numerical Study of the Aerodynamic Performance of a Brimmed Diffuser‑Augmented Offshore Wind Turbine across a Range of Tip‑Speed Ratios

This study presents a comprehensive CFD assessment of a brimmed diffuser augmented offshore wind turbine (BDAWT) versus a conventional three blade horizontal axis offshore wind turbine (HAWT) across a tip speed ratio (TSR) range of 4–10. High fidelity steady RANS simulations employing the SST k–ω turbulence model were conducted, with a rigorous mesh independence verification using up to 2.7 million cells. We extracted global performance metrics—namely the power coefficient (C_P)—as well as detailed local flow data: axial velocity and static-pressure profiles on four characteristic cross sections (upstream of the rotor, diffuser throat, diffuser outlet vertical plane, and diffuser outlet horizontal plane), along with the corresponding velocity ratios. Compared with the baseline HAWT, the brimmed diffuser pre accelerates the core flow by up to ~25%, induces a pronounced low-pressure suction region at the diffuser throat, and narrows the downstream wake. These effects collectively raise the peak C_P from 0.39 to 0.59 and shift the optimal TSR from 7 to 8. Furthermore, boundary layer separation on the blades is delayed in the BDAWT, and the local velocity ratio exceeds unity at the diffuser exit, confirming sustained flow acceleration through the rotor. The detailed pressure distributions and wake recovery trends provide quantitative guidance for optimizing diffuser geometry and brim angle. Our results lay a solid foundation for subsequent experimental validation and facilitate the practical deployment of high efficiency diffuser-augmented offshore wind turbines in real world renewable energy applications.