Modeling of filament-based free vortex wake method for horizontal axis wind turbines: A review

The continuing growth of wind-turbine size, blade flexibility, offshore deployment, and wind-farm control requirements is increasing the need for aerodynamic models that retain wake physics at a computational cost suitable for engineering design. Blade element momentum methods remain efficient but depend on empirical wake and induction corrections, whereas high-fidelity computational fluid dynamics is often too expensive for long aeroelastic, floating-platform, and multi-turbine simulations. Filament-based free vortex wake (FVW) methods provide an intermediate-fidelity alternative by representing blade-bound and wake vorticity explicitly and recovering induced velocity through the Biot–Savart law. This review summarizes the theoretical foundation and current state of filament-based FVW methods for horizontal-axis wind turbines. The discussion is organized around the modeling workflow: vorticity–velocity formulation, projection of blade and wake vorticity, Lagrangian wake advection, induced-velocity regularization, diffusion and core growth, stretching treatment, circulation convergence, dynamic-stall coupling, computational acceleration, and engineering applications. Particular attention is given to the distinctions among lifting-line, lifting-surface, vortex-lattice, thick-panel, filament, ring, and reduced-wake formulations. By connecting the governing vorticity equations with practical implementation choices and recent applications, the review clarifies the capabilities, limitations, and future development needs of filament-based FVW methods for large, flexible, floating, and interacting wind turbines.