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Yacht sail flow: recent findings and unanswered questions

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Original languageEnglish
Publication statusPublished - 2015
Event6th Conference on Computational Methods in Marine Engineering (Marine 2015) - Rome, Italy
Duration: 15 Jun 201517 Jun 2015

Conference

Conference6th Conference on Computational Methods in Marine Engineering (Marine 2015)
CountryItaly
CityRome
Period15/06/1517/06/15

Abstract

This paper aims to review the current knowledge in yacht sail aerodynamics and, in particular, on the characteristic flow features of foresails. Yacht sails are flexible low-aspect-ratio 3D thin wings, which experience a complex 3D turbulent wind and which are capable of developing remarkably high aerodynamic forces. Sail aerodynamics includes a wide range of flow features, spanning from the leading-edge vortex typical of, for instance, insect flyers, to the laminar separation bubble typical, for instance, of low-speed turbo compressors. Our knowledge on the flow field around sails derived from numerical simulations, while quantitative flow measurements have never been performed. Surface pressure distributions were measured with both model- scale sails in wind tunnels and with full-scale sails on the water. These experiments allowed a good understanding of the pressure distributions on sails but limited insights on the correlated local flow field. On the other hand, numerical modelling of sails requires large computational resources because of the complex flow field with separation on curved surfaces and because of the high sensitivity of the flow field to the local angle of attack at the sharp leading edge. Therefore high-fidelity numerical simulations, such as for instance wall-resolved Large Eddy Simulations, have never been attempted before. Less computationally intense hybrid methods (Detached Eddy Simulations) have showed that a leading-edge vortex contributes significantly to the lift of asymmetric spinnakers and that trailing-edge separation occurs at about half of the sail’s chord; while a flow field similar to a laminar separation bubble develops from the leading edge of staysails, where trailing edge separation is minimal. However the inability of these numerical methods to resolve accurately the laminar to turbulent transition and the flow at the wall, has led several paramount questions unanswered, such as for instance the effect of the Reynolds number and of the onset turbulence on the performance of sails.

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