Takeoff of a hydrofoil vessel in Panship

Abstract

Recently the interest in hydrofoil vessels using a fully submerged hydrofoil increased. Hydrofoil vessels experience a resistance hump and possible instabilities during their takeoff of which both are influence by waves. In order to determine the required power during the takeoff to overcome the resistance hump and to investigate whether the hydrofoil vessel is stable during the takeoff numerical simulations or experiments have to be performed. Experiments covering the full takeoff require a long towing tank and high towing velocities and therefore these experiments are costly. The alternative, performing numerical simulations, is favorable but requires a suitable numerical code. As no validated code is available in which a takeoff can be performed in waves, in this research Panship, a potential flow code suitable for high speed craft and adapted for use with hydrofoil craft, is validated for the takeoff of a hydrofoil vessel. In this research the results of Panship are compared with results of experiments and other numerical codes in four different stage as little validation data is present for the takeoff of a hydrofoil vessel. The four different stages are: a foil without the influence of the free surface, a foil with the influence of the free surface, two foils with the influence of the free surface and the hull and foil system near during the takeoff. In these four stages the lift and drag determined in Panship is compared with available experimental results and numerical codes. As the simulations in Panship require a vast amount of input parameters, the influence of these parameters is studied first to ensure the reliability of the results. Comparing the results of Panship for a deeply submerged foil with another potential flow solver shows that the lift is predicted correctly, but that the induced drag is underpredicted. If viscous effects are required in the solution, the quality of the results of Panship is dependent on the type of hydrofoil used. As some foils have a large viscous effect on lift, the lack of viscosity on Panship, leads to a low quality of the results for lift and induced drag as they are overpredicted. The trends for interaction of a foil with the free surface are predicted correctly but the underprediction of induced drag influences the quality of the results. Panship is able to predict the effects of foil interaction for lift correctly, but the results for foil interaction for drag are poorer. During the takeoff Panship is able to predict the lift fairly correct but the total drag is underpredicted severely. Recommendations are given to improve the results of Panship and for future work.