Trans RINA, Vol 153, Part B2, Intl J Small Craft Tech, 2011 Jul-Dec PERFORMANCE OPTIMIZATION OF INTERACTING SAILS THROUGH FLUID


STRUCTURE COUPLING (DOI No: 10.3940/rina.ijsct.2011.b2.119)


V G Chapin and N de Carlan, Institut Supérieur de l’Aéronautique et de l’Espace, Université de Toulouse, France P Heppel, Peter Heppel & Associates, France SUMMARY


In this paper, the problem of sailing yacht rig design has been addressed through the development of a computational framework based on viscous Computational Fluid Dynamic (CFD) modelling for the aerodynamic part and on a non linear structural modelling for the structure part. The Fluid Structure Interaction (FSI) coupling used is a loose coupling. The interest but


also the expertise needed to use Reynolds Averaged Navier-Stokes (RANS) equations for the


aerodynamic modelling is justified through examples and validations with a focus on complex separated flow configurations. The originality of the presented computational framework is its ability to address complex, non linear optimization problems with a derivative free evolutionary strategy. This capability is enhanced by the fact that it is based on a remeshing technique rather than on a deforming mesh one.


After the description of the main elements of this


computational framework for Fluid Structure Interaction, it is used for generic sail optimization problems and for the rig design of a 18 footer to illustrates its capabilities and limitations to produce accurate aeroelastic solutions on sailing yacht rigs.


NOMENCLATURE i





C, c Cd Cl


Clmax Ch Cr Cp D 


* m f


f/c


f /c* Fh Fr g


i i* many


Entry angle of the sail Apparent wind angle Sail chord


Drag coefficient Lift coefficient


Maximum lift coefficient Heeling force coefficient Driving force coefficient Pressure coefficient Drag force


Sail trim angle


Optimal sail trim angle Mainsail trim angle Foresail trim angle Sail camber


Optimal sail camber Heeling force Driving force


Overlap (longitudinal distance between the jib clew and the mast) Angle of attack = -


L Lift force L/D


xf/c VA 1.


(L/D)max Maximum lift-to-drag ratio Mc S


Sail surface


Chord-wise coordinate of the maximum camber


Apparent wind velocity INTRODUCTION


The design of interacting sails for highly competitive sailing yachts is a multidisciplinary design problem addressed by sail designers, sailors and scientists over


Optimal angle of attack = -* Lift-to-drag ratio Heeling moment


years considerations


[1-3]. Sail from


design is an art using membrane structures


and


aerodynamics. The sail designer wishes to have a better knowledge of the global three-dimensional flow around sails with particular attention on wakes and peculiar phenomena linked to rig layout. He/she is interested in obtaining a quantitative analysis of aerodynamic loads and structural stresses and their dependency on design changes. This is part of the design process.


Historically, many papers have addressed a part of these questions from various scientific points of view [1-5]. This research has shed some light on sail design questions and their main parameters such as sail aspect ratio, camber, entry angle, optimal angle of attack, sail interaction, mast effect, coupling mechanism between the mainsail and the foresail, upwind and downwind sailing conditions, sail twist and atmospheric boundary layer, flow separation, fluid structure interaction, etc...


In a more general sense, this membrane design problem is a complex multidisciplinary


problem at the


crossroads of the research developments needed in fluid structure coupling with numerous fields of application. This complex and multidisciplinary problem implies that various approaches are currently in development with


various hypotheses. Rigorous comparisons


between each of them are of great benefit in promoting a critical mind in a community where passion is sometimes dominant.


For the aerodynamic part of the FSI problem, some existing tools are based on inviscid modelling [6, 7] and some are based on viscous flow modelling [8, 9, 10].


Velocity Prediction Programs (VPP) that are frequently used in sailing yacht design are based on empirical aerodynamic and hydrodynamic models to predict aero- hydrodynamic forces and their dependences to design


©2011: The Royal Institution of Naval Architects B-103


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