The present work discusses an upwind case study about full scale measurements gathered during navigation on the Politecnico di Milano Sailing Yacht Laboratory (SYL). SYL is a 10m sailing boat, consisting in standard instrumentation, integrated dynamometer, a 3D flying shape detection system and distributed pressure sensors on sails. Particular attention was devoted to pressure measurements: full scale results are analysed and compared with wind tunnel test. The comparison of full scale/wind tunnel pressure distributions holds consistently, with the highest differences observed in the regions close to the leading edge. Critical aspects related to performing full scale measurements are also discussed.

Computational methods currently form a significant part of a sailing yacht design project. The fluid-dynamics that characterises a sailing yacht is extremely complex, due to the fact that the yacht is partly immersed in water and partly in air with major three-dimensional and turbulent phenomena. A large number of investigations, using both experimental and numerical methods, have created an extensive knowledge of the physics of a sailing yacht, but at the same time highlighted the extent and complexity of this research field. A better understanding of the physics involved in both the aerodynamics and fluid dynamics of the yacht, together with the need to develop, improve and validate existent numerical models are primary reasons to further extend the work done on this subject. There have been a number of studies of the aerodynamics of upwind sails. Viola (Viola et al., 2013) modelled the air flow field around a hypothetical AC33 class yacht design, using a steady RANS solver, and highlighted the main flow features and structures involved in upwind sailing aerodynamics. Even though the flow is mainly attached to the sails, numerical results showed areas of leading edge flow separation, especially at the top of the mainsail, where the influence of the downwash generated by the headsail is less predominant. Querard & Wilson (Querard & Wilson, 2007) and Masuyama (Masuyama et al., 2007) showed the need for a high quality, fine mesh in order to capture these flow features and correctly reproduce the pressure distribution on the sail surface. Queutey (Queutey et al., 2015) addressed some misbehaviour of numerical models to geometric incongruities with the experimental benchmark model. The present work further investigates upwind sailing aerodynamics, analysing the effects of geometric and mesh modifications, in combination with the use of Large Eddy Simulation. LES has proven its ability to model highly turbulent and separated flow (Sagaut & Mary, 2001) (Sampaio et al., 2014), albeit at the expense of high computational costs. To date there are no published results of LES in sailing aerodynamics, and so the application of the methodology to the modelling of a well documented experiment (Fluck, 2010) allows the testing of LES’s capabilities and applicability to this field of research. A high resolution grid was used so as to capture the finest flow structures trying to correctly reproduce the pressure distribution across the sails, especially in regions of flow separation. Particular effort was made to replicate the experimental test conditions and to analyse the influence that different set ups have on the computational results. Simulations were performed using RANS and LES on the same mesh, allowing a direct comparison between the methods.

The structural design of a racing yacht is aimed at lowering the centre of gravity and mass of the boat within strength constraints in order to increase the sail carrying ability and reduce hull drag...