Development of forces around a hydrofoil appendage of a sailing boat

Abstract

Hydrofoils are adopted for many modern sailing classes both for multihulls and single hull boats. America's Cup boats have hydrofoils at their appendages (keel and/or rudder). Recently the ISAF choose the NACRA 17 class with modern designed foils as Olympic Class for the 2020 Olympic Games. These modern designed foils lift the hull out of the water, reducing the wetted surface and the resistance of the hull as well as the wave resistance of the boat and therefore they increase the speed of the boat. A sailing hydrofoil can achieve speeds exceeding two times the wind speed. All these great advantages of the innovative foil configurations are in the State of the Art of the design of modern racing boats. However, it should be noticed, that the use of such foils causes many times instabilities due to the development of increased forces and moments (not symmetric base). In the present work an attempt is made to investigate numerically the development of forces and moments around a modern foil. The numerical solution of RANS equations is based on incompressible finite volume method, developed by the author, which has the capability to deal with complex geometries. The k-ε model in conjunction with the wall functions is employed to model the turbulence characteristics. In order to verify the code numerical tests are firstly performed on a NACA0012 3D wing (foil). Then, the code is applied to solve the flow field past of cambered 3D NACA0012 foil, in order to evaluate the forces and moments. Several configurations (L, J, etc.) are tested and results of drag, side force and lift are compared to find the most affective configuration. All tests are made at 4 degree of leeway angle. by solving numerically the fundamental RANS (Reynolds averaged Navier-Stokes) equations in a finite computational grid which is generated around the foil. In the present work the differences between several configurations are examined and the important task is to understanding these differences and the precise of each value that of course suffer from uncertainties (very fine grid, turbulence modeling, precision established) are less important. The results presented in this investigation have been produced by software developed by the first of the authors. DESCRIPTION The numerical codeThe Continuity Equation & Navier Stokes Equation in vector form, independent of the coordinate system, for an incompressible fluid at time stable, could be written:where ρ: fluid density, V: is the vector of velocity, σ: stress tensor, Sv: source tensor and V ⊗V tensor product.

Injury and illness surveillance at the International Sailing Federation Sailing World Championships 2014

“…The newer classes, namely the 49er (since the 2000 Olympics), 49erFX and Nacra 17 (both debuting at the 2016 Olympics), are fast and inherently unstable 4 5. The physiological demands on the sailor are position-specific and class-specific 6 7.…”