Full-scale flying shape measurement of offwind yacht sails with photogrammetry

Abstract

Yacht downwind sails are complex to study due to their non-developable shape with high camber and massively detached flow around thin and flexible membranes. Numerical simulations can now simulate this strong Fluid-Structure Interaction, but need experimental validation. It remains complex to measure spinnaker flying shapes partly because of their inherent instability, like luff flapping. This work presents full-scale experimental investigation of spinnaker shapes with simultaneous measurement of aerodynamic loads on the three sail corners, with navigation and wind data. The experimental setup and photogrammetric method are presented. Results are analysed in the whole range of apparent wind angle for this sail. The spinnaker shape shows dramatic variations and high discrepancies with the design shape. The photogrammetric measurement produces the full 3D flying shape with a satisfactory accuracy. Even if only steady state results are given here, this new system enables time-resolved measurement of flying shapes and thus flapping of spinnakers to be investigated, which is valuable for yacht performance optimisation. On top of sailing yacht applications, the method is useful in any application where a non-developable 3D shape is to be determined, and particularly when it results from the Fluid Structure Interaction of a flexible structure with a complex flow.

Experimental analysis of a strong fluid–structure interaction on a soft membrane—Application to the flapping of a yacht downwind sail

“…The average sail shape, pressure distribution and loads are significantly different between small and large angles (see Fig. 8 and also Motta et al, 2015;Deparday et al, 2016;Deparday, 2016). For large angles, the flow is mainly detached around the sail, the apparent wind speed lower hence the aerodynamic loads smaller.…”

“…The spinnaker sail is used for a wide range of wind angles and speeds. Therefore, its shape and its aerodynamic loads vary widely with the wind Deparday et al, 2016). The flow seen by the sails (called Apparent Wind) is the vector sum of the wind (called True Wind) and the opposite yacht velocity.…”

“…The sail shape was measured during other experimental campaigns in the same conditions thanks to photogrammetry, as described in Deparday et al 2016, where a detailed analysis of the sail shape is made for different sailing conditions (wind angle particularly). In the present work, the focus is on the dynamics of pressures and the previously measured sail shapes are only used to draw the pressure spatial patterns (see Fig.…”

“…Non dimensional numbers for MAV and Flag are taken respectively from Rojratsirikul et al (2011) and Connell and Yue (2007 (Rojratsirikul et al, 2011). When the structure is very flexible such as a membrane, large deformations are expected and the fluid-structure coupling may be strong, particularly if the membrane is not highly constrained (Glück et al, 2001;Knight et al, 2010;Durand et al, 2014;Michalski et al, 2015;Deparday et al, 2016;Chae et al, 2016;Tiomkin and Raveh, 2017;Waldman and Breuer, 2017).…”

Parametric Sail Analysis of Sailing Yachts in 9-20 Meters

“…[9]. Deparday çalışmalarını tek bir tekne ve yelken için yapmış olup, yelken üzerine yerleştirdiği ölçüm aletleri ile farklı açılarda gelen rüzgârın karakteristik sonuçlar üzerindeki etkisini incelemiştir [10]. Katamaran teknelerin yelkenlerinde oluşan kuvvetleri saptamak için Cella, HAD programları ile 5 farklı tipte yelken modeli incelemiştir.…”