A Comparison of a RANS Based VPP to on the Water Sailing Performance

Abstract

This paper compares performance predictions from a Reynolds Averaged Navier Stokes (RANS) based Velocity Prediction Program (VPP) to on the water testing of a J70. The J70 has been outfitted with a system to determine sail flying shapes, apparent wind conditions and performance data. The on the water testing is conducted in both racing and controlled sailing conditions. Data taken during racing conditions is analyzed to determine optimal performance envelopes while data taken in controlled conditions is used to match exact sailing and VPP states. The data acquisition system combines a number of standard marine sensors including a sonic anemometer, a GPS, a digital compass, an accelerometer and a gyroscope with custom sensors that measure rudder and boom angles as well as a custom sail shape acquisition system. The RANS based VPP developed by Doyle CFD has three main components; an aerodynamic force model, a hydrodynamic force model and an algorithm to balance the forces. The force balance routine uses four degrees of freedom; boat speed, yaw, heel and rudder angle to balance the aerodynamic and hydrodynamic forces for a given true wind speed and angle. The force models are derived from RANS CFD data calculated using OpenFOAM. The aerodynamic forces are calculated using steady state RANS as a function of apparent wind angle, apparent wind speed and sail flying shape. The VPP force model is derived by fitting response surfaces to this data. The aerodynamic CFD is run with sail flying shapes recorded from on the water testing. Using accurate flying shapes is critical for picking out slight aerodynamic differences in sail and rig setup. The hydrodynamic CFD data points are calculated using RANS Volume of Fluid CFD (VOF) as a function of boat speed, rudder angle, yaw angle, heel angle and displacement. Response surfaces are generated from a 64 data point array of RANS VOF simulations.