CFD and potential flow assessment of the hydrodynamics of a kitefoil

Kitefoil boards are a novel, emerging and disrupting class of sailing crafts, with major economical implications for the tourism sector due to their capability to enable kitesurfing in light wind areas. This paper investigates the hydrodynamics of the underwater appendage of a state-of-the-art kitefoil with a potential flow panel method implemented in the open source code Apame and with the Navier-Stokes solver ANSYS Fluent. The first objective has been to establish a valid range for the potential flow method predictions. It has been found that the potential flow panel method renders similar forces than those obtained using CFD, in the typical cruise range. Moreover, in leeway incidence conditions, additional drag originating from the fuselage, where potential assumptions are not applicable, represents less than 10% of the overall drag. These results enable potential flow panel methods to be used as design tools for this kind of devices, in particular the open source solver used in this study, whose large computational efficiency is a major advantage considering the number of headings that have to be considered to feed velocity-prediction-programs. The second objective has been to investigate the system of forces and moments in the appendage during navigation. The way the various elements of the craft interact (main and rear foil, mast, kite and rider) under different sailing conditions is explained based on the hydrodynamic forces obtained with the numerical methods used.