Particle Image Velocimetry: Experimental Flow Visualisation for Wind-Assisted Ship Wings and Yacht Sails

Wind-assisted ships and racing yachts employ highly cambered profiles to maximise performance. However, their complex aerodynamics governed by flow separation remains to be fully understood. Particle image velocimetry (PIV), performed in water tunnels, may lead to breakthroughs, provided fundamental spatial and temporal resolution limitations are overcome. Consequently, force measurements and flow visualisation were undertaken on circular arcs and yacht sails 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 relaminarisation of the boundary layer downstream of the leading-edge separation bubble. Ultimately, PIV in water tunnels is shown to be a pertinent methodology. These findings provide novel insights into the aerodynamics of wind-assisted ships and yachts and may contribute to improving their performance by design.