Fluid Structure Interaction of Yacht Sails in the Unsteady Regime

The dynamic Fluid Structure Interaction (FSI) of yacht sails submitted to a harmonic pitching motion is numerically investigated to address both issues of aerodynamic unsteadiness and structural deformation. The model consists in an implicit dynamic coupling algorithm between a Vortex Lattice Method model for the aerodynamics and a Finite Element Method model for the structure dynamics. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces oscillation shows hysteresis phenomena and equivalent damping and stiffening effects of the unsteady beahvior. The area of the hysteresis loop increases with the motion reduced frequency and amplitude. In the case of a rigid structure, the aerodynamic forces oscillations and the exchanged energy are lower than for a flexible structure.The authors are grateful to Prof. Fossati of Politecnico di Milano for valuable discussions and to the K-Epsilon company for continuous collaboration. This work was supported by the French Naval Academy