DEVELOPMENT OF A WIND-TUNNEL TEST FACILITY FOR YACHT AERODYNAMIC STUDIES

Wind-tunnel tests on scale models of yachts are very difficult to carr y out accurately because of the complicated aerodynamics and boundary conditions associated with the full-scale situation. Yachts sail at th e interface between water and air. The water surface is not smooth, an d the yacht orientation and wind strength vary with time. In addition, the sails behave somewhat like slender aerofoils for some sailing dir ections, and whereas like bluff bodies at others. This paper addresses some of the simplifying assumptions which must be made in order to ma ke practical wind tunnel measurements on scale models of yachts. It de scribes a wind tunnel and balance facility which has been developed in the Mechanical Engineering Department of the University of Auckland t o measure and process the aerodynamic forces and moments generated by wind flowing over yacht sails. The development of a linearised version of Galway's force balance calibration method to process the balance d ata is described, This simplified version confers significant advantag es in the real-time operation of the balance. Finally, the usefulness of the facility is illustrated with some results obtained during the s tudy of a Twelve Metre America's Cup Yacht sailing downwind under spin naker.