Recent Advances Wind-Assisted Ship and Yacht Sail Aerodynamics

Wind-assisted ships and racing yachts employ highly cambered sections to maximise performance. However, their complex aerodynamics governed by large regions of flow separation remain to be fully understood. Recently, particle image velocimetry (PIV), performed in water tunnels, has been suggested as a novel experimental technique, provided fundamental spatial and temporal resolution limitations are overcome. Consequently, force measurements and flow visualisation were undertaken on 2D circular arcs, representative of a wind-assisted ship wing, and 3D downwind yacht sails, namely symmetric spinnakers, to ascertain the viability of this experimental approach. The results show that (i) a linear blockage correction can be devised; (ii) a blockage-independent critical Reynolds number and critical angle of attack exist; and (iii) a force crisis occurs because of the suppressed relaminarization of the boundary layer downstream of the leading-edge separation bubble. As such, spatial and temporal limitations can be overcome, yielding novel insights into sail aerodynamics, with PIV in water tunnels shown to be a pertinent methodology for experimental flow visualisation. These findings provide new insights into the aerodynamics of wind-assisted ships and yachts and may contribute to improving their performance by design.