OBJECTIVES

It is the goal of the Downwind Aero Moments and Forces project to improve the accuracy of modern handicapping rules in understanding downwind aerodynamic performance. By collaborating with those sailmakers using FSI modeling, this project will produce a set of results comprised of all aerodynamic moments and forces for a range of downwind sails, angles, and wind speeds utilizing RANS code coupled with finite element analysis results. These results will be made publicly available and will serve as a valuable validation source for the improvement of VPP.

METHODS

Using fluid-structure interaction (FSI) modeling, the project simulated three yachts that represent a range of performance for typical modern racing yachts. A modified TP52, Swan42, and McCurdy and Rhodes 48 were simulated with A2 and A3 sail plans and configurations, with an S2 configuration also being simulated for the latter. Sail designs were created using North Sails’ “Global DesMan Design Base” and were then used by North’s design suite to create the 3D finite element analysis (FEA) models. Using North’s FEA tool “MemBrain,” these models were coupled with OpenFOAM to get a converged solution, with sail trim adjusted between each iteration to achieve neutral luff pressure. Simulations were meshed to identify the differences in sail forces and moments through a range of sail designs and boat performance. Sailing conditions were taken from the current performance targets provided for each boat, with leeway set to zero in all cases, and simulations onset flow defined at 10 meter elevation at true wind speeds of 8, 12, and 16 knots. Additionally, a heel sweep and traveler sweep were done in TWS 12 without changes to the sail trim, other than rotating the main’s foot angle +/- 5 degrees throughout the traveler sweep.