Sail trimming FSI simulation - Comparison of viscous and inviscid flow models to optimise upwind sails trim

A numerical comparison between two FSI models, based on inviscid and viscous flow solvers, is presented in this paper. The differences between aerodynamic coefficients, sail flying shape and pressures computed by both FSI tools are investigated for medium wind conditions. These differences are evaluated for different values of the main sheet length. The study has shown very close results when the main sheet is not over trimmed for medium true wind speed, but discrepancies increase when flow separation becomes significant. Then, an optimisation procedure based on inviscid FSI is performed to optimise the main sheet and car trims, in order to maximise an objective function based on the driving and side forces, in a case of low true wind speed. Limitations of the inviscid flow hypothesis are highlighted and the difficulties to use inviscid FSI models in an optimisation procedure, for a case of low true wind speed, are shown