Fluid-Structure Interaction of a Foiling Craft

Abstract

Hydrofoils are a current hot topic in the marine industry both in high performance sailing and in new passenger transport systems in conjunction with electric propulsion. In the sailing community, the largest impact is seen from the America’s cup, where boats are sailed at more than 50 knots (over 100 km/h) with 100% “flying” time. Hydrofoils are also becoming popular in the Olympics, as in the 2024 Olympic games 5 gold medals will be decided on foiling boats/boards. The reason for the increasing popularity of hydrofoils and foiling boats is the recent advances in composite materials, especially in their strength to stiffness ratio. In general, hydrofoils have a very small wetted surface area compared to the wetted surface area of the hull. Therefore, after “take-off” speed, the wetted surface area of the hull, and consequently the resistance of the boat, is reduced considerably. The larger the weight of the boat and crew and the higher the speeds, the greater the loads on the hydrofoils will be. The current research investigates the interaction effects between the fluid and structure of the ZP00682 NACRA 17 Z-foil. The study is carried out both experimentally, in SSPA’s cavitation tunnel, and numerically using a fully coupled viscous solver with a structural analysis tool. The experimental methodology has been used to validate the numerical tools, which in turn are used to reverse engineer the material properties and the internal stiffness of the NACRA 17 foil. The experimental flow speed has been chosen to represent realistic foiling speeds found in the NACRA 17 class, namely 5, 7, and 9 m/s. The forces and the deflection of the Z-foil are investigated, showing a maximum deflection corresponding to 24% of the immersed span. Finally, the effects of leeway and rake angles on the bending properties of the Z-foil are investigated to assess the influence of different angles in sailing strategies, showing that a differential rake set-up might be preferred in search for minimum drag.

Dynamic Fluid Structure Interaction of NACRA 17 Foil

“…The solid model is based on solid FEM and the fluid flow model is based on RANS FVM. The work is an extension of the work presented in [8,14,20]. In [8] FSI of the NACRA 17 foil is investigated both experimental and numerical.…”

“…The work is an extension of the work presented in [8,14,20]. In [8] FSI of the NACRA 17 foil is investigated both experimental and numerical. The experimental investigation are used also in the present paper for validation.…”

“…It is common to use a Finite Element Model (FEM) to solve the solid problem. The complexity of the models varies from simple beam elements [1,3,5,7,[9][10][11][12] to the more complex shell [6][7][8][9] and solid elements [2] and in some cases even considering anisotropic material properties. The fluid flow problem can also be solved with varying degrees of complexity from lifting line method [3,12] to unsteady Reynolds Average Navier-Stokes (RANS) Finite Volume Methods (FVM) [6].…”

“…The numerical model is validated by comparing it to an experimental campaign conducted at RISE SSPA Maritime Center in Sweden. In this experiment, described in detail in [8], the NACRA 17 z-foil is mounted in a water tunnel exposed to high flow speeds, representative of sailing loads, while forces and deflection are monitored. Furthermore, the numerical model is verified by detailed mesh studies of both solid model and fluid flow model.…”

“…Modern hydrofoils are thin to reduce drag and the tin structure results in large deformations during sailing and therefore Fluid Structure Interaction (FSI) are important. In recent years much work has been published on FSI of foils, see for example [1][2][3][4][5][6][7][8][9][10][11][12].…”