AC75 aerodynamic performance prediction via BEM

The AC75 class, used in the America’s Cup, is a hydro-foiling racing sailing yacht powered by a double-skin main sail and a single-skin jib. The boat performance is typically predicted by a Velocity Prediction Program (VPP). The aerodynamics are usually modeled with surrogate models of data points collected either through wind tunnel experiments, numerical simulations, or empirical formulations. Previous work has shown that empirical models are not able to predict accurate performance as the sailors can efficiently control the flying shape of each sail. In addition, the empirical coefficients are limited to traditional sails, not yet available for a double-skin main, neglecting also the hull shape and its influence on the sails airflow. To achieve more realistic results through the inclusion of hull shape with realistic sail geometries and shape ranges, a compromise must be found between total computational effort and physical simplifications. Reynolds Averaged Navier-Stokes (RANS) methods typically provide accurate predictions but come with a high computational effort. Potential flow-based methods, also used by America’s Cup teams, are computationally less expensive while showing some limitations at higher angles of attack with flow separation. Due to the high number of simulations required for a surrogate model at the early design stage, a Boundary Element Method (BEM) was considered appropriate for the task in combination with a RANS method for comparison. Results have shown that the BEM is able to predict reasonable forces generated by the single-skin jib and double-skin main. The performance deltas with endplated sails on the hull with attached vortices, comply with expected trends.

Subjects

DDC Class

600: Technology

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AC75 aerodynamic performance prediction via BEM