THE EFFECT OF WIND-PROFILE AND TWIST ON DOWNWIND SAIL PERFORMANCE

The flow over a pair of downwind sails, a mainsail and spinnaker, is s uccessfully modelled using the finite volume package CFDS-FLOW3D. An i nvestigation of the effects of wind twist on the performance of the sa ils tends to suggest that the major effect is the result of the modifi ed wind profile in the case of twisted flow. The thrust and side force coefficients for logarithmic flow are shown to be similar to publishe d data obtained from wind tunnel tests. Flow visualisation illustrates how the flow is primarily attached to the sails at an apparent wind a ngle of 100 degrees but is almost completely separated at an angle of 140 degrees.