Graf, K. and Renzsch, H.: RANSE Investigations of Downwind Sails and Integration into Sailing Yacht Design Processes, Proc. High Performance Yachting Conference II, Auckland/NZ, Jan. 2006
A fluid structure interaction method has been developed to calculate the viscous turbulent flow around flexible trimmable downwind sails. The structural part of the method is based on a Finite Element presentation of the sail modelled as a membrane. Minimization of the total potential energy function using a quasi Newton type method is carried out to calculate the displacement of the sail under aerodynamic loads. The flow around the deformed sail is calculated solving the Reynolds Averaged Navier Stokes Equation using a Finite Volume approach. The method is iterative by nature with consecutive cyclic investigations of structure and flow. The implementation of this method is based on the CFX commercial RANSE code using it's plug-in technique of FORTRAN code for the structural part. A procedure has been set up to simulate the process of trimming the sail corresponding to wind tunnel tests. As a first test case a comparison of two symmetric downwind sails of an IMS 600 yacht has been chosen. The design shape of sails has been imported from a sail-makers lofting program. The flying shape of the sails has been calculated. Lift and drag coefficients have been compared for the fixed and flexible sail. A comparison of these coefficients with those calculated from the IMS sail force method shows reasonable good agreement.
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