Flow simulations for wind-tunnel studies of sail aerodynamics

Abstract

The aerodynamic of yacht sails is described in order to highlight some of the difficulties which arise when wind-tunnel investigations using scale models are carried out. It is shown that exact similitude of full-scale is impossible to achieve in the wind-tunnel due to the complex nature of the full-scale flow and the conflicting requirements of the relevant dimensionless scaling parameters. The main difficulties are that the sails may approximate both streamlined and bluff bodies, depending on whether the yacht is sailing up- or down-wind, and that the relative motion of the yacht and wind introduces a height variation into the apparent wind direction and speed. Various remedies for these difficulties are outlined, together with the important factors related to obtaining useful date from wind-tunnel studies. These factors can be subdivided into test section wind structure, testing procedures and model construction. Recommendations regarding the methods required to achieve the best results are presented.