Evaluating an Enhanced Hydrodynamic Lifting Line Model of a Hydrofoil

Abstract: Hydrofoils have become a popular design addition to different kinds of vessels, particularly yachts and race boats. Predicting hydrodynamic forces acting on hydrofoils remains challenging, due to a wide operating regime and complex hydrodynamical phenomena. In this paper we investigate the accuracy of a lifting-line (LL) model-modified to account for wave-making and free surface effects using a Green function representing the potential of a source in steady motion under a free surface by benchmarking its predictions against previously-validated computational fluid dynamics (CFD) simulations. A rectangular NACA4412 hydrofoil was simulated fully submerged at Reynolds numbers between 2.57x10^5 and 2.06x10^5, which corresponded to chord-based Froude numbers between 0.5 and 4. First, the total drag forces were evaluated and compared. When wave-making was included in the LL model, it was able to adequately predict the Froude-dependent trend in drag force from CFD. However, it was unable to sufficiently model the magnitude of the drag force, especially at intermediate Froude numbers, likely due to a lack of ability to simulate various non-linear and viscous effects. Downstream induced downwash predictions were also evaluated and compared, with excellent agreement seen between LL and CFD. The accuracy of the LL model demonstrated here can be greatly exploited for exploring a large design space to optimise candidate designs during preliminary conception thanks to its efficiency compared to traditional CFD. Keywords: Hydrofoil, Computational fluid dynamics, Lifting line, Hydrodynamics, Waves