Numerical and Experimental Studies of Sail Aerodynamics

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(1)Departamento de Arquitectura y Construcción Navales Escuela Técnica Superior de Ingenieros Navales Universidad Politécnica de Madrid. PhD Thesis. Numerical and Experimental Studies of Sail Aerodynamics. By. Ms. Patricia Izaguirre Alza M.Sc. in Naval Architecture. Supervisor: Prof. Luis Pérez Rojas Ph.D. in Naval Architecture Professor in Ship Theory. 2012.

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(3) Abstract The purpose of this investigation was the determination of the aerodynamic performance of sails and gain knowledge of the phenomena involved in order to improve the aerodynamic characteristics. In this research, the airflow around different sails in four scenarios was studied. The method to analyze these scenarios was the combination of numerical simulations and experimental tests by taking advantage of the best of each tool. Two different Computational Fluid Dynamic codes were utilized: the ANSYS-CFX and the CD-Adapco’s STAR-CCM+. The experimental tests were conducted in the Atmospheric Boundary Layer Wind Tunnel at the Universidad de Granada (Spain), the Twisted Flow Wind Tunnel at the University of Auckland (New Zealand) and the A9 Wind Tunnel at the Universidad Politécnica de Madrid (Spain). Through this research, it was found the three-dimensional effect of the mast on the aerodynamic performance of an IMS Class boat. The pressure distribution on a Transpac 52 Class mainsail was also determined. Moreover, the aerodynamic performance of the 43ft and 60ft Dhow Classes was obtained. Finally, a feasibility study was conducted to use a structural wing in combination with conventional propulsions systems. The main conclusion was that this research clarified gaps on the knowledge of the aerodynamic performance of sails. Moreover, since commercial codes were not specifically designed to study sails, a procedure was developed. On the other hand, innovative experimental techniques were used and applied to model-scale sails. The achievements of this thesis are promising and some of the results are already in use by the industry on a daily basis.. iii.

(4) iv. Resumen El propósito de este estudio era determinar el comportamiento aerodinámico de unas velas y mejorar el conocimiento de los fenómenos que suceden para optimizar las caracterı́sticas aerodinámicas de dichas velas. En esta investigación se estudió el flujo de aire alrededor de diferentes velas en cuatro escenarios. El método para analizar estos escenarios fue la combinación de simulaciones numéricas y ensayos experimentales mediante el aprovechamiento de las ventajas de cada herramienta. Se utilizaron dos códigos de dinámica de fluidos computacional: el ANSYS-CFX y el STAR-CCM+ de la empresa CD-Adapco. Los ensayos experimentales se desarrollaron en el túnel de viento de capa lı́mite de la Universidad de Granada (España), el túnel de viento de la Universidad de Auckland (Nueva Zelanda) y en el túnel A9 de la Universidad Politécnica de Madrid (España). Mediante esta investigación, se determinó el efecto tridimensional del mástil en un velero de la clase IMS. También se describió la distribución de presiones sobre una mayor de un Transpac 52. Además, se obtuvo el comportamiento aerodinámico de las clases 43ft y 60ft de los veleros Dhows. Finalmente, se llevó a cabo un estudio de viabilidad de la utilización de un ala estructural en combinación con sistemas de propulsión convencionales. La conclusión principal de esta investigación fue la capacidad de explicar ciertas lagunas en el conocimiento del comportamiento aerodinámico de las velas en diferentes escenarios. Además, dado que los códigos comerciales no están especı́ficamente diseñados para el estudio de velas, se desarrolló un procedimiento a tal efecto. Por otro lado, se han utilizado innovadoras técnicas experimentales y se han aplicado a modelos de velas a escala. Los logros de esta investigación son prometedores y algunos de los resultados obtenidos ya están siendo utilizados por la industrı́a en su dı́a a dı́a..

(5) Acknowledgments I’m very grateful to the following people and institutions for their assistance during this research: • Professor Luis Pérez Rojas, my supervisor and boss. I will never be able to thank him enough for his support, encouragement and guidance. ¡Gracias jefe! • The members of the CEHINAV group (Juan, Paco, Rian, Ricardo A., Ricardo Z., Jorge, . . . ) . They have not only helped on the research but they have looked after me during this process. I need to highlight the contribution of Alberto Torres and Adriana Oliva, who have helped me obtaining some of the results of this research. I’m particularly grateful to José Luis Cercós for his invaluable assistance in my computers. • Professor Richard G.J. Flay, David J. Le Pelley and the Yacht Research Unit of the University of Auckland (New Zealand). They gave me a warm welcome to their research group. They helped me grow as a person and as a researcher. Furthermore, they gave me the opportunity to discover New Zealand, one of the most beautiful places that I have ever visited. • Shaun Connolly, David Parr and Calibre Sails Ltd. They provided the dhow sails for free and guided me during the investigation. Thanks Shaun, for letting me meet your family and share with them the “kiwi” lifestyle. • Volker H. Rosenkranz and the EU-CargoXpress project. The collaboration with Volker and the project have allowed me not only obtaining very interesting results but traveling and meeting inspiring people. • José Marı́a Terrés, Jessika Garcı́a and the Wind Engineering group of the Centro Andaluz de Medio Ambiente (Spain). I have to thank them for accepting me and opening the doors of their facilities for my investigation. They helped, support and guided me during the research. • Sebastián Franchini, Javier Pérez and the Instituto Universitario de Microgravedad “Ignacio Da Riva” at the Universidad Politécnica de Madrid (Spain). I’m grateful for their work on the experimental tests and their valuable suggestions. v.

(6) vi. • Professor Yutaka Masuyama. He provided me worthwhile information and his permission to use his experimental results. • I have to highlight that this research has been partially funded by a PhD scholarship of the Universidad Politécnica de Madrid. • Quiero agradecer a mi aita, a mi ama, a Gloria, a toda mi familia, por el amor, el apoyo incondicional, por aguantarme, por mantenerme, por todo, eskerrik asko! Y cómo no, a Israel, mi compañero, el que ha soportado cada lágrima, cada ataque de ansiedad, cada momento de histeria y siempre ha estado a mi lado. Esta tesis ha sido posible gracias a todos vosotros..

(7) Contents 1 INTRODUCTION 1.1 General problem . . 1.2 Motivation . . . . . . 1.3 Scope . . . . . . . . 1.4 Contributions . . . . 1.5 Outline of the thesis. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. 1 2 3 4 4 5. 2 SAILING CONCEPTS 2.1 Nomenclature . . . . . . . . . . . . . . . 2.2 Balance of the aero/hydrodynamic forces 2.3 Aerodynamic Force . . . . . . . . . . . . 2.4 Sail Interaction . . . . . . . . . . . . . . 2.5 Apparent Wind . . . . . . . . . . . . . . 2.6 Conclusion . . . . . . . . . . . . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. 7 7 9 10 15 16 18. . . . . . . .. 21 21 22 25 25 33 34 35. . . . . . . . . .. 39 39 40 42 42 42 43 43 45 46. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. 3 LITERATURE REVIEW 3.1 Performance Prediction . . . . . . . . . . 3.1.1 Wind Tunnel Tests . . . . . . . . 3.1.2 Full-scale Tests . . . . . . . . . . 3.1.3 Numerical Simulations . . . . . . 3.2 Aeroelastic Analysis . . . . . . . . . . . 3.2.1 Fluid Structure Interaction (FSI) 3.3 Optimization approaches . . . . . . . . . 4 WIND TUNNEL TESTS 4.1 Nomenclature . . . . . . . . . . . . 4.2 History . . . . . . . . . . . . . . . . 4.3 Types . . . . . . . . . . . . . . . . 4.3.1 Based on the airflow speed . 4.3.2 Based on the return circuit . 4.3.3 Based on the test section . . 4.3.4 Special-purpose tunnels . . . 4.4 Operation and design . . . . . . . . 4.4.1 Operation . . . . . . . . . . vii. . . . . . . . . .. . . . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . .. . . . . . . .. . . . . . . . . ..

(8) viii. CONTENTS. 4.5. 4.4.2 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Measurements and Instrumentation . . . . . . . . . . . . . . . . . . . . . . 50. 5 COMPUTATIONAL FLUID DYNAMIC SIMULATIONS 5.1 Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Mathematical Model . . . . . . . . . . . . . . . . . . . . . . 5.2.1 General conservation law . . . . . . . . . . . . . . . . 5.2.2 Levels of approximation . . . . . . . . . . . . . . . . 5.2.3 Boundary Conditions . . . . . . . . . . . . . . . . . . 5.3 Space Discretization . . . . . . . . . . . . . . . . . . . . . . 5.3.1 Types . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2 STAR-CCM+ Mesh . . . . . . . . . . . . . . . . . . 5.3.3 Mesh Validity and Quality . . . . . . . . . . . . . . . 5.4 Discretization of Equations . . . . . . . . . . . . . . . . . . . 5.4.1 Continuity Equation . . . . . . . . . . . . . . . . . . 5.4.2 Momentum Equation . . . . . . . . . . . . . . . . . . 5.4.3 RANS Turbulence Models . . . . . . . . . . . . . . . 5.4.4 Wall Treatment . . . . . . . . . . . . . . . . . . . . . 5.4.5 Gradient Computation . . . . . . . . . . . . . . . . . 5.4.6 SIMPLE Solver Algorithm . . . . . . . . . . . . . . . 5.5 Solution: Time Integration Method . . . . . . . . . . . . . . 5.6 Solution: Algebraic System of Equations . . . . . . . . . . . 6 INFLUENCE OF THE MAST 6.1 Introduction . . . . . . . . . . . . . . . 6.2 Nomenclature . . . . . . . . . . . . . . 6.3 Measurements of full-scale performance 6.4 Tests with ANSYS-CFX . . . . . . . . 6.4.1 Domain and mesh . . . . . . . . 6.4.2 Boundary conditions . . . . . . 6.4.3 Numerical scheme . . . . . . . . 6.4.4 Results and comparison . . . . 6.5 Tests with STAR-CCM+ . . . . . . . . 6.5.1 Domain and mesh . . . . . . . . 6.5.2 Boundary conditions . . . . . . 6.5.3 Numerical scheme . . . . . . . . 6.5.4 Results and comparison . . . . 6.6 Conclusions . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. 55 59 62 62 65 66 67 68 69 70 71 72 75 79 82 84 87 88 89. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. 93 93 95 96 99 100 101 102 102 110 111 112 113 113 122. 7 PRESSURE DISTRIBUTION ON A TP52 MAINSAIL 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Transpac 52 Class . . . . . . . . . . . . . . . . . . . . . . . 7.3.1 Brief History . . . . . . . . . . . . . . . . . . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. 123 123 125 125 127. . . . . . . . . . . . . . . . . . . and sail shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . ..

(9) CONTENTS. 7.4. 7.5. 7.6. ix. Experimental tests . . . . . . . . . . . . . . . . . . . . . 7.4.1 Wind tunnel description . . . . . . . . . . . . . . 7.4.2 The model . . . . . . . . . . . . . . . . . . . . . . 7.4.3 Experimental set-up and test description . . . . . 7.4.4 Results . . . . . . . . . . . . . . . . . . . . . . . . Numerical simulations . . . . . . . . . . . . . . . . . . . 7.5.1 Domain and mesh . . . . . . . . . . . . . . . . . . 7.5.2 Boundary conditions . . . . . . . . . . . . . . . . 7.5.3 Numerical scheme . . . . . . . . . . . . . . . . . . 7.5.4 Comparison between simulations and experiments Conclusions . . . . . . . . . . . . . . . . . . . . . . . . .. 8 AERODYNAMICS OF SAILING DHOWS 8.1 Introduction . . . . . . . . . . . . . . . . . . . . 8.2 Nomenclature . . . . . . . . . . . . . . . . . . . 8.3 The Dhow . . . . . . . . . . . . . . . . . . . . . 8.3.1 History of the Dhow . . . . . . . . . . . 8.3.2 The Dhow nowadays . . . . . . . . . . . 8.4 Experimental Tests . . . . . . . . . . . . . . . . 8.4.1 Wind tunnel description . . . . . . . . . 8.4.2 The model . . . . . . . . . . . . . . . . . 8.4.3 Experimental set-up and test description 8.4.4 Results . . . . . . . . . . . . . . . . . . . 8.4.4.1 43ft Dhow Model . . . . . . . . 8.4.4.2 60ft Dhow Model . . . . . . . . 8.5 Numerical simulations . . . . . . . . . . . . . . 8.5.1 Geometry . . . . . . . . . . . . . . . . . 8.5.2 Domain and mesh . . . . . . . . . . . . . 8.5.3 Boundary conditions . . . . . . . . . . . 8.5.4 Numerical scheme . . . . . . . . . . . . . 8.5.5 Results . . . . . . . . . . . . . . . . . . . 8.6 Conclusions . . . . . . . . . . . . . . . . . . . . 9 EU-CARGOXPRESS PROJECT 9.1 Introduction . . . . . . . . . . . . . . . . . 9.2 Nomenclature . . . . . . . . . . . . . . . . 9.3 Existing technologies . . . . . . . . . . . . 9.4 The project . . . . . . . . . . . . . . . . . 9.4.1 Description . . . . . . . . . . . . . 9.4.2 Conclusions of the EU-CargoXpress 9.4.3 Contribution . . . . . . . . . . . . 9.5 Numerical simulations . . . . . . . . . . . 9.5.1 Geometries . . . . . . . . . . . . . 9.5.2 Domain and mesh . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . Project . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . .. 128 128 129 132 133 136 136 137 137 138 141. . . . . . . . . . . . . . . . . . . .. 143 . 143 . 145 . 146 . 146 . 147 . 150 . 150 . 153 . 155 . 158 . 158 . 165 . 169 . 169 . 170 . 171 . 172 . 172 . 175. . . . . . . . . . .. 177 . 177 . 178 . 180 . 184 . 184 . 186 . 187 . 187 . 187 . 189.

(10) x. CONTENTS. 9.6. 9.7. 9.8. 9.5.3 Numerical scheme and boundary conditions 9.5.4 Results . . . . . . . . . . . . . . . . . . . . . Experimental Tests . . . . . . . . . . . . . . . . . . 9.6.1 Wind tunnel description . . . . . . . . . . . 9.6.2 The model . . . . . . . . . . . . . . . . . . . 9.6.3 Experimental set-up and test description . . 9.6.4 Results . . . . . . . . . . . . . . . . . . . . . Feasibility study . . . . . . . . . . . . . . . . . . . . 9.7.1 Routes . . . . . . . . . . . . . . . . . . . . . 9.7.2 Wind characteristics . . . . . . . . . . . . . 9.7.3 Energy saving . . . . . . . . . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . .. 190 190 192 193 194 195 197 200 200 200 202 205. 10 CONCLUSIONS. 207. A Mast effect data with STAR-CCM+. 211. B Second set of tests: results. 213. C Yard Stiffness Scale. 215. D 43ft Dhow Model Tests. 217. E 60ft Dhow Model Tests. 223. F 43ft Dhow Model Results. 225. G 60ft Dhow Model Results. 241. H Energy Scenarios. 247. I. 249. Wind tunnel results. J Numerical results. 253.

(11) List of Figures 1.1. Volvo Ocean Race 2008-2009. Start of the Leg 1 in Alicante (Spain) . . . .. 2.1 2.2 2.3 2.4 2.5 2.6 2.7. Force balance . . . . . . . . . . . . . . . . Points of sail . . . . . . . . . . . . . . . . Flow around a sail . . . . . . . . . . . . . Components of the total aerodynamic force Flow around a mast/sail combination . . . Flow around a mainsail/jib combination . Planetary boundary layer and the twist . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. 9 10 11 12 14 16 17. 4.1 4.2 4.3 4.4. Whirling arm . . . . . . . . . . . Close-section, open-circuit tunnel Open-section, close circuit tunnel Pitot tube . . . . . . . . . . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. 41 48 49 51. 5.1 5.2 5.3. Post process with the STAR-CCM+ . . . . . . . . . . . . . . . . . . . . . . 57 Polyhedral mesh with prism layers . . . . . . . . . . . . . . . . . . . . . . . 69 Trimmer mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70. 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12 6.13 6.14 6.15 6.16. Sail dynamometer boat Fujin . . . . . . . . . . . . . . . . . . . . . . . . . 94 ID96092335 case mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Pressure distribution (ID9807172F) . . . . . . . . . . . . . . . . . . . . . . 105 Pressure distribution (ID9807172B) . . . . . . . . . . . . . . . . . . . . . . 106 Pressure distribution (ID96092335) . . . . . . . . . . . . . . . . . . . . . . 106 Plane at half of the luff of mainsail (ID9807172B) . . . . . . . . . . . . . . 107 Two vortices downstream (ID9807172B) . . . . . . . . . . . . . . . . . . . 108 ID9807172F case mesh with a mast . . . . . . . . . . . . . . . . . . . . . . 109 Increase of the number elements vs. elapsed time per iteration (computer 1)110 Domain of the ID9807172B case with mast . . . . . . . . . . . . . . . . . . 112 Force coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 Center of effort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Pressure coefficient distribution (ID9807172F with mast) . . . . . . . . . . 116 Pressure coefficient distribution (ID9807172F without mast) . . . . . . . . 117 Normalized speed and streamlines (ID9807172F) . . . . . . . . . . . . . . . 117 Normalized speed (ID96092335) . . . . . . . . . . . . . . . . . . . . . . . . 118. . . . .. xi. . . . .. . . . .. . . . .. . . . .. 1.

(12) xii. LIST OF FIGURES. 6.17 6.18 6.19 6.20 6.21. Pressure coefficient (ID9807172F with and without mast) . . . . . . . . . . Pressure coefficient (ID96092335 with and without mast) . . . . . . . . . . Generation of vortices (ID9807172F) . . . . . . . . . . . . . . . . . . . . . Maximum vorticity (ID9807172F) . . . . . . . . . . . . . . . . . . . . . . . Maximum vorticity downstream, (ID9807172F, identical downstream mesh). 118 119 120 120 121. 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9. TP52 Class yacht Balearia (2005) . . . . . . . . . . . . Atmospheric boundary layer wind tunnel at CEAMA . The model . . . . . . . . . . . . . . . . . . . . . . . . . Sections and sensors . . . . . . . . . . . . . . . . . . . The model in the wind tunnel . . . . . . . . . . . . . . Pressure coefficients, first set of tests . . . . . . . . . . Midsection plane mesh . . . . . . . . . . . . . . . . . . Computed pressure coefficient distribution (windward) Wind tunnel data vs CFD results . . . . . . . . . . . .. . . . . . . . . .. . . . . . . . . .. . . . . . . . . .. . . . . . . . . .. . . . . . . . . .. . . . . . . . . .. 126 128 129 131 133 135 137 138 140. 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11 8.12 8.13 8.14 8.15 8.16 8.17 8.18 8.19 8.20 8.21 8.22 8.23 8.24. A 43ft dhow racing . . . . . . . . . . . . . . . . . . . . . . . . . . A 60ft dhow sailing in Dubai . . . . . . . . . . . . . . . . . . . . . The Twisted Flow Wind Tunnel at the University of Auckland . . Plan of the wind tunnel . . . . . . . . . . . . . . . . . . . . . . . The model fitted with the 43ft rigging and winches . . . . . . . . 43ft dhow model during a test with stiffeners . . . . . . . . . . . . 43ft model, CX . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43ft model, CMX . . . . . . . . . . . . . . . . . . . . . . . . . . . 43ft model, CX/CMX . . . . . . . . . . . . . . . . . . . . . . . . 43ft model, CX vs HA . . . . . . . . . . . . . . . . . . . . . . . . 43ft model, CMX vs HA . . . . . . . . . . . . . . . . . . . . . . . 43ft model, Optimum Trimming Test, CX and CMX (AWA=60◦ ) 43ft model, Optimum Trimming Test, CX/CMX (AWA=60◦ ) . . . 43ft model, Bending Test, CX and CMX . . . . . . . . . . . . . . 43ft model, Bending Test, CX/CMX . . . . . . . . . . . . . . . . 43ft model, Yard Stiffness Test, CX/CMX . . . . . . . . . . . . . 60ft model, Basic Test, CX, CMX and CX/CMX . . . . . . . . . 60ft model, Basic Test with mizzen, CX and CMX . . . . . . . . . 60ft model, Optimum Trimming Test, CX, CMX and CX/CMX . Flying shapes: experimental, original and customized . . . . . . . Pressure coefficient distribution . . . . . . . . . . . . . . . . . . . Pressure coefficient . . . . . . . . . . . . . . . . . . . . . . . . . . Normalized speed at the midsection . . . . . . . . . . . . . . . . . Vortices downstream . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . .. 144 148 150 152 153 157 159 160 161 162 162 163 163 164 165 166 167 168 168 171 173 174 174 175. 9.1 9.2 9.3. Solar Albatros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 Buckau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Alcyone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183. . . . . . . . . .. . . . . . . . . .. . . . . . . . . .. . . . . . . . . .. . . . . . . . . ..

(13) LIST OF FIGURES. 9.4 9.5 9.6 9.7 9.8 9.9 9.10 9.11 9.12 9.13 9.14 9.15 9.16. xiii. Beluga-SkySails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . EU-CargoXpress Project . . . . . . . . . . . . . . . . . . . . . . . . . . . First (red), second (blue) and third geometry (green) . . . . . . . . . . . The third geometry in the numerical domain . . . . . . . . . . . . . . . . Force coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Saved power at 15knots of vessel speed (second and third geometries) . . A9 IDR/UPM wind tunnel . . . . . . . . . . . . . . . . . . . . . . . . . . Pressure model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sensor distribution, leeward(left) and windward(right) (Dimensioning in mm) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Models of the third geometry . . . . . . . . . . . . . . . . . . . . . . . . Force coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pressure coefficient, experimental vs numerical results . . . . . . . . . . . Effective power (EHP) compare to the expected power (Psail ) . . . . . . .. . . . . . . . .. 184 185 188 189 191 192 193 194. . . . . .. 195 196 197 199 204. B.1 Pressure coefficient, second set of tests . . . . . . . . . . . . . . . . . . . . 213 F.1 F.2 F.3 F.4 F.5 F.6 F.7 F.8 F.9 F.10 F.11 F.12 F.13 F.14 F.15 F.16 F.17 F.18 F.19 F.20 F.21 F.22 F.23 F.24 F.25 F.26 F.27. 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft. model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model,. Basic Test: CX vs AWA. . . . . . . . . . . . . . . . . . . Basic Test: CMX vs AWA. . . . . . . . . . . . . . . . . . Basic Test: CX/CMX vs AWA. . . . . . . . . . . . . . . . Basic Test: CD vs AWA. . . . . . . . . . . . . . . . . . . Basic Test: CL vs AWA. . . . . . . . . . . . . . . . . . . Basic Test: CX vs HA. . . . . . . . . . . . . . . . . . . . Basic Test: CMX vs HA. . . . . . . . . . . . . . . . . . . Bent Yard Test: CX vs AWA. . . . . . . . . . . . . . . . Bent Yard Test: CMX vs AWA. . . . . . . . . . . . . . . Bent Yard Test: CX/CMX vs AWA. . . . . . . . . . . . . Bent Yard Test: CD vs AWA. . . . . . . . . . . . . . . . Bent Yard Test: CL vs AWA. . . . . . . . . . . . . . . . . Bent Yard Test: CX vs HA. . . . . . . . . . . . . . . . . Bent Yard Test: CMX vs HA. . . . . . . . . . . . . . . . Optimum Trimming Test: CX vs HA (AWA=40◦ ) . . . . Optimum Trimming Test: CMX vs HA (AWA=40◦ ) . . . Optimum Trimming Test: CX/CMX vs HA (AWA=40◦ ) . Optimum Trimming Test: CX vs HA (AWA=60◦ ) . . . . Optimum Trimming Test: CMX vs HA (AWA=60◦ ) . . . Optimum Trimming Test: CX/CMX vs HA (AWA=60◦ ) . Optimum Trimming Test: CX vs HA (AWA=80◦ ) . . . . Optimum Trimming Test: CMX vs HA (AWA=80◦ ) . . . Optimum Trimming Test: CX/CMX vs HA (AWA=80◦ ) . Bending Test: CX vs AWA. . . . . . . . . . . . . . . . . . Bending Test: CMX vs AWA. . . . . . . . . . . . . . . . Bending Test: CX/CMX vs AWA. . . . . . . . . . . . . . Yard Stiffness Test: CX vs AWA (HA=0◦ ) . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 225 225 226 226 226 227 227 227 228 228 228 229 229 229 230 230 230 231 231 231 232 232 232 233 233 233 234.

(14) xiv. LIST OF FIGURES. F.28 F.29 F.30 F.31 F.32 F.33 F.34 F.35 F.36 F.37 F.38 F.39 F.40 F.41 F.42 F.43 F.44 F.45 F.46. Stiffness Stiffness Stiffness Stiffness Stiffness Stiffness Stiffness Stiffness Stiffness Stiffness Stiffness Stiffness Stiffness Stiffness Stiffness Stiffness Stiffness Stiffness Stiffness. Test: Test: Test: Test: Test: Test: Test: Test: Test: Test: Test: Test: Test: Test: Test: Test: Test: Test: Test:. CMX vs AWA (HA=0◦ ) . . . CX/CMX vs AWA (HA=0◦ ) . CD vs AWA (HA=0◦ ) . . . . CL vs AWA (HA=0◦ ) . . . . . CX vs AWA (HA=5◦ ) . . . . CMX vs AWA (HA=5◦ ) . . . CX/CMX vs AWA (HA=5◦ ) . CD vs AWA (HA=5◦ ) . . . . CL vs AWA (HA=5◦ ) . . . . . CX vs AWA (HA=10◦ ) . . . . CMX vs AWA (HA=10◦ ) . . . CX/CMX vs AWA (HA=10◦ ) CD vs AWA (HA=10◦ ) . . . . CL vs AWA (HA=10◦ ) . . . . CX vs AWA (HA=15◦ ) . . . . CMX vs AWA (HA=15◦ ) . . . CX/CMX vs AWA (HA=15◦ ) CD vs AWA (HA=15◦ ) . . . . CL vs AWA (HA=15◦ ) . . . .. 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft 43ft. model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model, model,. Yard Yard Yard Yard Yard Yard Yard Yard Yard Yard Yard Yard Yard Yard Yard Yard Yard Yard Yard. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. 234 234 235 235 235 236 236 236 237 237 237 238 238 238 239 239 239 240 240. G.1 60ft G.2 60ft G.3 60ft G.4 60ft G.5 60ft G.6 60ft G.7 60ft G.8 60ft G.9 60ft G.10 60ft G.11 60ft G.12 60ft G.13 60ft G.14 60ft. model, model, model, model, model, model, model, model, model, model, model, model, model, model,. Basic Test: CX vs AWA (with and without mizzen) . . . Basic Test: CMX vs AWA (with and without mizzen) . . Basic Test: CX/CMX vs AWA (with and without mizzen) Basic Test: CD vs AWA (with and without mizzen) . . . Basic Test: CL vs AWA (with and without mizzen) . . . Basic Test: CX vs HA . . . . . . . . . . . . . . . . . . . . Basic Test: CMX vs HA . . . . . . . . . . . . . . . . . . Basic Test: CX vs HA (without mizzen) . . . . . . . . . . Basic Test: CMX vs HA (without mizzen) . . . . . . . . Optimum Trimming Test: CX vs HA . . . . . . . . . . . Optimum Trimming Test: CMX vs HA . . . . . . . . . . Optimum Trimming Test: CX/CMX vs HA . . . . . . . . Optimum Trimming Test: CD vs HA . . . . . . . . . . . Optimum Trimming Test: CL vs HA . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. 241 241 242 242 242 243 243 243 244 244 244 245 245 245. H.1 Energy balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248.

(15) List of Tables 6.1 6.2 6.3 6.4 6.5 6.6. Sail dimensions . . . . . . . . . . . . . . . . . . . Sail shapes . . . . . . . . . . . . . . . . . . . . . . Sailing conditions . . . . . . . . . . . . . . . . . . Measured data . . . . . . . . . . . . . . . . . . . Comparison of results, reference vs present study Comparison of results, with and without a mast .. 7.1 7.2 7.3. Main dimension limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 Pressure tap location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 The tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134. 8.1 8.2 8.3 8.4 8.5. Model-scale hull dimensions . . The rigging dimensions . . . . . The yards dimension . . . . . . Summary of the conducted tests Comparison of results . . . . . .. . . . . .. . . . . .. 154 154 158 159 172. 9.1 9.2 9.3 9.4 9.5 9.6. Main characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Main dimensions of the three geometries . . . . . . . . . . . . . . . . . . Routes and areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Relationship between waves and wind speed . . . . . . . . . . . . . . . . Annual probabilities for different wave heights . . . . . . . . . . . . . . . Annual probabilities for different wind directions for wave height less than 4m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Third geometry, sail power obtained with CFD data . . . . . . . . . . . . Third geometry, comparison between numerical (CFD) and experimental (WT) results (13 knots of vessel speed) . . . . . . . . . . . . . . . . . . .. . . . . .. 186 188 201 201 202. 9.7 9.8. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . . .. 97 98 98 99 103 109. . 202 . 203 . 203. A.1 Results of the simulations with and without the mast . . . . . . . . . . . . 211 C.1 Yard data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 D.1 D.2 D.3. 43ft model: Basic Test(BT) . . . . . . . . . . . . . . . . . . . . . . . . . . 217 43ft model: Bent Yard Test(BYT) . . . . . . . . . . . . . . . . . . . . . . 218 43ft model: Optimum Trimming Test(OPT) . . . . . . . . . . . . . . . . . 219 xv.

(16) xvi. LIST OF TABLES. D.4 D.5. 43ft model: Yard Stiffness Test (YST) . . . . . . . . . . . . . . . . . . . . 220 43ft model: Bending Test (BEN) . . . . . . . . . . . . . . . . . . . . . . . 222. E.1 E.2. 60ft model: Basic Test(BT) with and without mizzen . . . . . . . . . . . . 223 60ft model: Optimum Trimming Test(OPT) . . . . . . . . . . . . . . . . . 224. I.1. Pressure tap position and pressure coefficient . . . . . . . . . . . . . . . . 249. J.1. Pressure coefficient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253.

(17) Chapter 1 INTRODUCTION The sport of sailing is of prime importance for Spain. It is the sport which has achieved more Olympic (17) and gold (11) medals than any other sport in this country. The interest increased when the 32nd and 33rd America’s Cup races were held in Valencia in 2007 and 2010, respectively. Moreover, the start of the Volvo Ocean Race 2008/2009 and 2011/2012 also contributed to the media and economic impact. The America’s Cup is one of the world’s most important sports event and the oldest of the modern age. This race is not only sport but due to its special features and high media profile, it has become a first order economic phenomenon. As an example, and according to [1], “the holding in Valencia of the America’s Cup 2007 involved an injection of expenditure of such magnitude that it translated into an annual increase during three years of around 1% of the Gross Domestic Product (GDP) and employment of the Valencia Region, generating an accumulated total of 5,748 million of output, 2,724 million of value added and 73,859 jobs over the period 2004-07”. Another figure of the America’s Cup 2007: the budget of the Spanish Challenge in that race was about 60 millions. The Spanish sailing has also gotten involved in the Volvo Ocean Race. In 2008, the. Figure 1.1: Volvo Ocean Race 2008-2009. Start of the Leg 1 in Alicante (Spain) 1.

(18) 2. CHAPTER 1. INTRODUCTION. race start was held in Alicante (see figure 1.1) and two Spanish boats participated. It was estimated that the 2008/2009 race involved 80 millions of economic impact and generated 1,500 direct and indirect employments. Furthermore, the media impact was valued in 180 million euro and a million visitors at the Village. In 2011, the race start was held in Alicante as well and there was also an Spanish challenge. Again, the next race starts will be held in Alicante (2014 and 2017). These figures highlight that sailing is not just a sport but a profitable industry. Spain is getting involved and providing this sport with funds and resources. Nowadays, sailboats present high technology advances, a leading edge engineering and the use of the latest tools. There is a continuous research on sail aerodynamics but there are some gaps which this thesis tries to explain.. 1.1. General problem. The knowledge of the airflow around the rigging of a sailboat is indispensable for the resulting performance, and therefore, increased attention is being paid to this problem in order to gain a thorough understanding of the phenomena involved. Up to now, the sail designing has been mainly based on the experience of the designers and on experimental tests. The scientific community have considered that wind tunnel tests are more adequate to analyze the flow around sails despite some drawbacks such as the scale effect or the difficulty to measure some parameters. For example, it is troublesome to obtain the pressure distribution over the sail for different apparent wind angles or the vorticity downstream. Several complex devices are needed which are usually intrusive. The use of numerical tools to study the aerodynamic of sails is recent and it is on the increase since it is cheaper and faster comparing to experimental tests. Additionally, unlike in wind tunnel testing, numerical codes can provided, with simple models, a high amount of parameters on the sails and around them. The main disadvantage to trust on numerical results is that first, codes and procedures must be validated. Therefore, it is reasonable that numerical tools do not substitute experimental tests but complement them in order to develop an efficient and trustworthy design methodology. The thread of this thesis is the combination of experimental tests and numerical simulations in four different scenarios (IMS Class, Transpac 52 Class, Dhows and structural wings) to understand the sail performance..

(19) 1.2. MOTIVATION. 1.2. 3. Motivation. Numerical codes are widely used but the procedure and the results are not easily disclosed. This is due to the excessive secrecy of the high performance sailboat industry. There is a lack of information to validate new codes and the methodology that designers may use. Most of the publications of reference provide qualitative results instead of quantitative values. Moreover, commercial numerical codes are not specifically developed to study the aerodynamics of sails. There are some difficulties such as the analysis of lifting surfaces without thickness, the complex geometry of the rigging and the elasticity of sails. During this thesis four different scenarios have been emerged with the same philosophy: combine experimental tests with numerical codes to better understand the phenomena involved near the sails. Next, the motivations for each of the four investigations are described. First, the three-dimensional effect of the mast on the aerodynamic performance of an IMS Class boat has been studied. There are several two-dimensional studies that deal with the mast influence but there is a lack of three dimensional results. Second, the pressure distribution on a Transpac 52 Class mainsail has been determined. As far as this author can tell, when this investigation began, pressure distributions on three-dimensional upwind model-scale sails had never been published. This encouraged the author to carry out this research. Third, the aerodynamic performance of the 43ft Dhow Class has been obtained as well as the performance of the 60ft Dhow Class. This research has come up from the interest shown by different sailmakers and the Yach Reseach Unit (University of Auckland, New Zealand) on the performance of sailing dhows. As far as it is known, there haven’t been conducted any aerodynamic nor hydrodynamic tests of these boats. It has been impossible to find any technical article or report which describes dhows. Fourth, a feasibility study has been conducted to use a structural wing in combination with conventional propulsions systems. Due to the increase of the fuel cost and the environmental concern, the shipping industry has high requirements on propulsion technologies using offshore wind which is an endless energy source, free of charge, powerful at seas and renewable. The EU-CargoXpress project deals with this problem and the aerodynamic performance of different structural wings have been analyzed under the context of this thesis..

(20) 4. CHAPTER 1. INTRODUCTION. 1.3. Scope. The principal objective of this research is to establish a procedure to study the sail aerodynamics by combining the use of numerical viscous codes and experimental tests. Moreover, the specific objectives for each of the scenarios are:. • Evaluate the effect of the mast on the sail performance of an IMS Class rigging. • Measure the pressure distribution on a Transpac 52 Class mainsail. • Characterize the main parameters that affect the sail performance of sailing Dhows. • Study the viability of using a structural wing to reduce the fuel consumption and emissions on the EU-CargoXpress Project.. 1.4. Contributions. One of the main contributions of the research is the study of the three-dimensional effect of a mast on sail performance. Numerical results have been compared with full scale data. This investigation has been partially disclosed in the papers “Computational Study of Sail Performance of a Racing Yacht” presented at the 47◦ Congreso de Ingenierı́a Naval e Industria Marı́tima in 2008 [2] and “The Effect of the Mast on Sail Performance” prestented at the IV International Symposium on Yacht and Motor Boat Design and Production [3] in 2010. The pressure distribution on the three-dimensional upwind model-scale Transpac 52 Class mainsail have been measured in a wind tunnel. The experimental technique that has been used is widely spread in civil wind engineering but it is innovative in sail aerodynamics. Moreover, the tests have been reproduced with a numerical code. Another relevant achievement of this research is to be the first that has scientifically studied sailing dhows. These tests lay the grounds of future investigations. Both experimental and numerical tests have been conducted. The results of the experimental tests have been partially disclosed by the author in the report “Aerodynamics of Sailing Dhows” [4]. A methodology to study the viability of using structural wings combined with conventional propulsion systems has been also developed within the EU-CargoXpress Project. The aerodynamic performance of three different geometries have been compared numerically and then, the results have been validated with wind tunnel tests. The results of this investigation have been partially disclosed by the author in the paper “Viability Study of Sailing Propulsion combined with a Conventional System” presented at the XXII Congreso Panamericano de Ingenierı́a Naval, Transporte Marı́timo e Ingenierı́a.

(21) 1.5. OUTLINE OF THE THESIS. 5. Portuaria [5]. The author also collaborated on the report “Proposal for sustainable energy elaborated” of the Universidad Politécnica de Madrid [6]. Moreover, the paper “EU-CargoXpress: Wind Propulsion Concept” [7], written by this author and presented at the Transport Research Arena - Europe 2012, won the Best Paper Award. This highlights the relevance of this project and in particular, the innovative achievements of this author to the concern of the shipping industry.. 1.5. Outline of the thesis. The remainder of this thesis is the following. In chapter 2 the context is set. Chapter 3 puts the reader in the picture. The tools that have been used in this research are described in chapters 4 and 5. The four scenarios are presented in chapters 6, 7, 8 and 9. Finally, the conclusions are summarized in chapter10. Chapter 2 Sailing Concepts. In this chapter the basic ideas to understand the aerodynamics of sailing are presented. It is included an explanation of the aero/hydrodynamic balance of forces, the sail interaction, the apparent wind concept, as well as the nature of the aerodynamic force. Chapter 3 Literature review. Here, the research on sail aerodynamics is described. The tools to predict the performance of a sailboat, such as numerical simulations, wind tunnel and full scale tests, are presented. It is also included a description of the investigations related to aeroelastic studies and optimization approaches. Chapter 4 Wind tunnel tests. The history and types of wind tunnels are described in this chapter. Moreover, the operation and design are explained. It is also included a summary of the most common measurements that are acquired in wind tunnels and the instrumentation needed for those measurements. Chapter 5 Computational fluid dynamic simulations. In this chapter the basic concepts to understand a Computational Fluid Dynamic code are included. Furthermore, a description of the formulation and methodology used by the CD-Adapco’s STAR-CCM+ code are described. This chapter is particularized to the study of sail aerodynamics. Chapter 6 Influence of the mast. First, the reference full-scale tests are described as well as the sail shapes and the results for comparison. Then, the numerical simulations carried out with ANSYS-CFX are included. In the next section, the simulations performed with the CD-Adapco’s STAR-CCM+ code are presented. Finally, the conclusions are summarized. Chapter 7 Pressure distribution on a TP52 mainsail. First, the Transpac 52 Class is described. Then, the experimental test conducted at the Atmospheric Boundary Layer.

(22) 6. CHAPTER 1. INTRODUCTION. Wind Tunnel (Universidad de Granada, Spain) are included. In the next section, the numerical simulations are presented as well as the comparison of results. Subsequently, the conclusions are summarized. Chapter 8 Aerodynamics of sailing dhows. In this chapter, a description and the history of dhows are presented. Next, the experimental tests conducted at the Twisted Flow Wind Tunnel (University of Auckland, New Zealand) are described as well as the numerical simulations carried out with the STAR-CCM+ code. In the last section, there is a summary of the conclusions. Chapter 9 EU-CargoXpress project. First, the existing technologies are indicated. Next, the EU-CargoXpress project is briefly summarize. Then, the numerical simulations and the experimental tests are presented. These tests have been conducted at the A9 Wind Tunnel (Universidad Politécnica de Madrid, Spain). Subsequently, the feasibility study is described. In the last section, there is a summary of the conclusions that have been drawn. Chapter 10 Conclusions. In the last chapter of this thesis, the main conclusions are drawn..

(23) Chapter 2 SAILING CONCEPTS In this chapter, the basic sailing concepts are explained in order to better understand the studies that are described in this thesis.. 2.1. Nomenclature. β. Apparent wind angle. δm. Trim angle of the mainsail. A. Angle between lift (L) and total aerodynamic force (FT ). γ. True wind angle. λ. Leeway angle. µ. Air dynamic viscosity. ρ. Air density. ∆. Displacement. Θ. Heel angle. D. Drag force. FH. Total heeling force. FHlat. Horizontal heeling force. FR. Driving force. FS. Total side force. FSlat. Horizontal side force 7.

(24) 8. CHAPTER 2. SAILING CONCEPTS. FT. Total aerodynamic force. FV. Vertical aerodynamic Force. FV W. Vertical hydrodynamic force. g. Gravity. L. Lift force or cross wind force. Lc. Characteristic length. MH. Heeling moment. MP A. Aerodynamic pitching moment. MP W. Hydrodynamic pitching moment. MR. Righting moment. MY L. Hydrodynamic yawing moment. MY W. Aerodynamic yawing moment. R. Water resistance. Re. Reynolds number. V. Wind speed. VA. Apparent wind. VS. Boat speed. VT. True wind. W. Weight. z. Height, vertical distance. zref. Reference height. z0. Roughness length. Abbreviations CE. Center of effort.

(25) 2.2. BALANCE OF THE AERO/HYDRODYNAMIC FORCES. 2.2. 9. Balance of the aero/hydrodynamic forces. How does a sailing yacht navigate with a constant speed? This phenomenon is the consequence of the balance of the aerodynamic, hydrodynamic, buoyancy and gravity forces. As stated by [8], these forces, in turn, depend on the wind strength, the shape of sail, type of rig and control gadgets, the size and shape of the hull, displacement of the boat and distribution of weight, sea conditions and the crew’s level of expertise. The easiest and most common method to study the balance is to consider the forces acting separately and then, include the effect among them. In figure 2.1 (obtained from [9]) the components of these forces are illustrated, as well as the moments produced.. Figure 2.1: Force balance. The force/moment balance can be simplified to the resolution of six simple equations as presented in [9]: • Driving force (FR ) = Water resistance (R) • Horizontal heeling force (FHlat ) = Horizontal side force (FSlat ) • Vertical aerodynamic force (FV ) = Vertical hydrodynamic force (FV W ).

(26) 10. CHAPTER 2. SAILING CONCEPTS. • Aerodynamic pitching moment (MP A ) = Hydrodynamic pitching moment (MP W ) • Heeling moment (MH ) = Righting moment (MR ) • Aerodynamic yawing moment (MY M ) = Hydrodynamic yawing moment (MY L ) The difficulty arises when determine the components of the forces. In our case, the problem is focused on the aerodynamic force which depends not only on the wind strength but on the sail, the rig, mast and hull. It is also important to highlight that the aerodynamic force behaves differently depending on the angle between the wind and the boat. This concept is named “point of sail” as presented in figure 2.2 (obtained from [10]).. Figure 2.2: Points of sail. When a boat is sailing upwind, the angle of incidence of the apparent wind (concept explained in section 2.5) to the sail is small. The sails are pulled tight to the boat, the camber is small and the flow is mainly attached. In these conditions, sails act like traditional airfoils. The typical sloop-rig sailing boat uses the mainsail and a bow sail such as a genoa. If the angle of incidence of the apparent wind is larger, the point of sail is named “reach”. In this case, the mainsail is hoisted together with the gennaker or spinnaker. The flow is more complex since there is large scale separation. At the highest angles of incidence, the point of sail is called downwind (or run). The sails hoisted are the mainsail and the spinnaker. Here the flow is completely detached and becomes unsteady. The traditional airfoil theory cannot be applied in this situation. Therefore, the method to calculate the aerodynamic force depends on the point of sail in study, due to the different behavior of the flow in each case.. 2.3. Aerodynamic Force. But, where does the aerodynamic force come from? The sails have a profile around with the air flows. Due to the camber of the sail, the air on the leeward side has a higher.

(27) 2.3. AERODYNAMIC FORCE. 11. velocity comparing to the air on the windward side in order to verify the continuity of the field. According to the Bernoulli’s principle, the high speed flow provokes a reduction of pressure and therefore a suction comparing to the windward side of the sail. The aerodynamic force of a sail is a combination of the suction on leeward side and the pressure on windward side.. Figure 2.3: Flow around a sail. In figure 2.3 (obtained from [11]) the flow around a sail is plotted together with the pressure distribution on both sides. The aerodynamic force is the difference between the two curves (the pressure on each side). It can be seen that the major contribution to the force comes from the suction on the leeward side of the sail, as explained in [11]. In chapter 7, the pressure distribution on the windward side of a mainsail will be measured. In chapter 9, the pressure distribution on a rigid sail is calculated on both sides. The total aerodynamic force can be decomposed in two ways. The first method considers the driving (FR ) and heeling (FH ) components of the total force. This is used when studying the balance of the aero-hydrodynamic forces. But, when the aerodynamic behavior is analyzed by its own, it is a common practice to decompose the aerodynamic force in its lift (L) and drag (D) components as plotted in figure 2.4 (obtained from [9]). Drag has the direction of the apparent wind whereas the lift is perpendicular. Equation 2.1 shows the simple trigonometrical relation between the two methods of decomposition which depends on the apparent wind angle (β)..

(28) 12. CHAPTER 2. SAILING CONCEPTS. Figure 2.4: Components of the total aerodynamic force. FR = L sin β − D cos β FH = L cos β + D sin β. (2.1). It is obvious that the goal is to maximize the driving force and simultaneously minimize heeling force. When beating against the wind, the contribution of the drag is negative not only because it increases the heeling force but reduces the driving forces. The ratio L/D (or the angle between the lift and the total aerodynamic force) serve as an index of the aerodynamic efficiency. Therefore, in this point of sail, the objective is to maximize the lift and minimize the drag. As the apparent wind angle increases through the reaching point of sail, the contribution of the drag to the driving force becomes more important. At the last stage, when downwind, the maximum driving force will be equivalent to maximum drag. It can be seen that the study of the behavior of the drag is essential to understand the overall aerodynamic sail performance. Theory and experiments indicate that the drag (D) of a given rig is made up of four components: induced drag, friction drag, form (or pressure) drag and additional drag. Induced Drag Induced drag is produced in every lift-generating device and is manifested on the tip vortices. It is a rotating mass of air that is trailed behind sails and produces a continuous loss of wind kinetic energy. In chapter 6 the vortices are obtained with a numerical code.

(29) 2.3. AERODYNAMIC FORCE. 13. and the plot is included. The vortices are generated due to the difference of pressure on windward and leeward sides near the edges, foot and head. In those edges, the high pressure air on windward flows to the suction side on leeward, producing the tip vortices. Since the lift and the induced drag have the same origin this drag cannot be avoided but it can be reduced. Sail designers control the induced drag by three parameters. The first is the aspect ratio. Is is known that the higher the aspect ratio, the smaller the induced drag. This general statement should be considered together with other aspects than can be negative. For example, the heeling moments increase with the aspect ratio and the point of sail as mentioned before. The second parameter is the sail planform. An elliptic shape has low induced drag values whereas traditional triangular planforms have high values. Latest versions of high performance sails have a trapezoid shape with large heads. It has been proven that this shape has the benefits of the ellipctic shape not being detrimental to downwind sailing. The last parameter to control the induced drag is the gap between the boom and the deck. The boom can be lowered, or made wider or simply, the gab can be sealed. The objective is to prevent the air from flowing around the foot. Friction Drag The origin of the friction drag is the viscosity even though the direct effect is small. The problem arises because the viscosity generates the “boundary layer”. The layer, though thin, plays a crucial part in flow studies due to the shear stresses. Even for an incoming laminar flow, the shear stress provokes this flow become turbulent and increase the friction drag. In order to analyze if the transition from laminar to turbulent flow would occur, the Reynolds number (Re) is calculated (see equation 2.2, where ρ is the air density, µ is the air dynamic viscosity, V is the wind speed and Lc is the characteristic length which can be the camber of a section or the boom length, for example). It has been measured that the transition occurs approximately at Reynolds numbers around 5 · 105 . ρ · V · Lc (2.2) µ In the air (ρ ≈1.2 kg/m3 y µ ≈1.810−5 Ns/m2 ) the Reynolds number is approximately Re=Lc · V · 0.67 · 105 . For example, at 15knots of boat speed (7.7m/s), the transition from laminar to turbulent would occur at 65cm from the leading edge. Therefore, it is natural to think that in most cases, sails produce turbulent flow and consequently, an increase of the friction drag. Re =. But friction drag depends not only on the Reynolds Number but also on the smoothness of the sail surface. This affects the selection of the sailcloth. Thus, in order.

(30) 14. CHAPTER 2. SAILING CONCEPTS. to control the magnitude of the friction drag it is important to study the design, the trim when sailing and the sailcloth. Form (or pressure) Drag The form drag could be included in the friction drag since the origin of both is the air viscosity. But, it is convenient to consider both separately. This pressure drag arises from the separated flow which exists over some parts of a body (sail) in an air stream. It is named “form” because it is a consequence of the shape of the body. For example a large camber provokes flow detachment as well as the presence of a mast. The mast has a great influence in the speed performance since it disturbs the incoming flow to the sail. It generates turbulence and detachment. The flow can be attached again but the loss of energy would have already been produced.. Figure 2.5: Flow around a mast/sail combination. In figure 2.5 (obtained from [11]) the flow around a mast-sail configuration is shown. Three zones of separation can often be distinguished. As explained in [11], two are immediately behind the mast, to windward and leeward, respectively, while the third zone is on the aft part of the leeward side. This third zone depends on the forward separation and the loading of the sail. The main objective is always to improve the airflow pattern and thus to maximize the pressure differences between the windward and leeward sides of the mast-sail configuration. The adverse effect of a mast can be reduced by profiling it carefully, eliminating the gap between the mast and the sail, reducing the diameter and introducing turbulence stimulator. Moreover, the negative influence of the mast can be reduced by the sail sheeting. There is an optimum gab between sails that can reduce the form drag. In chapter 6 more information of the mast effect is included. Additional Drag.

(31) 2.4. SAIL INTERACTION. 15. The total area above waterline can be divided into two areas: sail and residual. This last generates the additional aerodynamic drag. Here the forces generated by the wind on the hull, rigging, mast and crew are taken into account. The impact of the additional drag to the total aerodynamic forces depends on the ratio between the sail and residual areas. The contribution of the additional drag is positive when sailing downwind but it does not compensate the losses that produces when sailing upwind. It is usually desirable to reduces as much as possible the effect of the parasitic area. Due to an appropriate design of the rigging, hull and superstructure, the additional drag can be reduced even though it will never be eliminated.. 2.4. Sail Interaction. When two or more sails are hoisted together, the interaction among them must be studied since their performance is not the sum of their contributions by their own. In figure 2.6 the easiest configuration is presented. There are two sails without the mast and sailing upwind. The thin lines are the streamlines for the single mainsail whereas the thick lines are the streamlines of the two sails in combination as presented in [11]. In the lower part of the figure the pressure curves are plotted. As it can be observed, the streamlines vary depending on the configuration. In the two-sail case the jib gets the load while the mainsail is unloaded, comparing to the single sail case. It is also observed that the presence of the jib modifies the suction side of the mainsail. The contribution of the mainsail to the total aerodynamic forces is reduced but there is a larger increase of the contribution of the jib. There are two theories that explain what happens between the two sails, which is called the “slot effect”. The traditional theory states that there is an increase of the airflow speed between the sails due to the Venturi effect. Recently, the second theory has demonstrated that the airflow speed decreases when reaching the gap between the sails. This makes the combination of the two sails behave as a single airfoil. If there is a suitable trimming, the lift generation of the combination of both sails is greater than the sum of each forces by their own. As mentioned in the previous section, the interaction between sails can also reduce the negative effects of the mast and prevent the flow from detaching..

(32) 16. CHAPTER 2. SAILING CONCEPTS. Figure 2.6: Flow around a mainsail/jib combination. 2.5. Apparent Wind. In real life, the onset flow onto a sail of a yacht (apparent wind, VA ) is not uniform. The flow has a vertical speed gradient and twist since the speed and direction of the flow change with height. This complex flow structure results from the vertical speed gradient in the atmospheric boundary layer (true wind, VT ) combined with the movement of the yacht (boat speed, VS ). In figure 2.7 (obtained from [12]) the true wind gradient is plotted in the left site while the apparent wind structure is presented on the right side. At sufficiently great heights above the surface of the earth, the influence of the friction of the wind along the ground becomes negligible. This region is called the free atmosphere. Within the atmospheric or planetary boundary layer the wind velocity is slowed down by the friction along the ground. The atmospheric boundary layer depth is typically between several hundred and 3km depending on the wind intensity, roughness of the terrain and angle of latitude. When considering yacht sails, only the lower portion.

(33) 2.5. APPARENT WIND. 17. Figure 2.7: Planetary boundary layer and the twist. of the boundary layer up to about 100m above the ground is of interest. The atmospheric wind in relation to sailing is called “true wind” (VT ). Extensive research has been conducted over the years to measure and describe the velocity profiles in boundary layers. In relation to the atmospheric boundary layer, the first representation of the wind profile in a horizontally homogeneous terrain was the power law proposed in 1916. Initially, it was assumed that the entire boundary layer depth could be approximated with a constant exponent. However, a number of experiments and real life observations have shown that only the lower fraction (∼ 10%) of the atmospheric boundary layer can be accurately described by a logarithmic velocity profile. In order to define the whole atmospheric boundary layer, empirical velocity profiles have been developed from theory and experiments, which are a combination of the logarithmic and power laws where the exponent varies with height. For the application to yacht sails the influence of the non-logarithmic terms can be ignored since the logarithmic law is known to hold well up to a height of at least 100m. Providing that the characteristic height of the sail is not larger than 100m, the true wind speed (VT ) at the height z can thus be calculated from the equation 2.3 where z0 is the terrain roughness length.. VT (z) = VT (zref ). ln(z/z0 ) ln(zref /z0 ). (2.3). For open waters, the roughness length (z0 ) is a function of the wave height, which again, it is a function of the wind speed. Cook [13] thus gives the roughness length as equation 2.4 where zref is 10m above the water and g is the acceleration due to gravity..

(34) 18. CHAPTER 2. SAILING CONCEPTS. z0 ≈ 5 · 10−5. VT (zref )2 g. (2.4). According to this equation, for typical true wind speeds between 5m/s and 20m/s, the roughness lengths would range from 0.13mm to 2.04mm. Clearly, ocean waves are larger than these roughness lengths, but their crests are rounded enough for the flow to follow the curvature without separating, which reduces the friction and in turn, the roughness length. Moreover, ocean waves travel in the direction of the wind, which reduces the speed differential, friction and roughness length. This expression for z0 is generalized. If not fully developed waves are to be considered, then an enhanced expression would be required. Similarly, the logarithmic law only applies for homogeneous terrain and gradient wind. For winds close to shore, another expression could be more convenient. As mentioned before, the variation of true wind speed with height affects the apparent wind velocity in magnitude and direction for each sail section. The apparent wind angle and speed for different heights resulting from the constant yacht speed and the logarithmically increasing true wind speed is shown in figure 2.7, as mentioned before. It can be seen that both the apparent wind speed and angle increase with height above the water. The apparent wind angle (β) and speed (VA ) can be calculated from the geometric relationship at any height z with equations 2.5 and 2.6, where λ is the leeway angle (which is usually ignored in the wind tunnel) and VT varies logarithmically with z as shown in equation 2.3.. β(z) = tan−1. VA (z) =. VT (z) sin(γ + λ) −λ VT (z) cos(γ + λ) + Vs. β[0, 180◦ ]. p Vs2 + VT (z)2 + 2VS VT (z) cos(γ + λ). (2.5). (2.6). The structure of the apparent wind is relevant to the problem of deliberate twisting of the sails. It is recommended that each section of the sail should operate at the same effective angle of incidence relative to the apparent wind. Furthermore, rolling and pitching should be taken into account due to their influence on the apparent wind strength and direction, because of the associated movements of the mast and sails. The effect is greatest toward the top of the mast, where the motion is more violent.. 2.6. Conclusion. It can be concluded that there are many factors affecting aerodynamic forces: sail setting (sheeting), heel angle, wind velocity and turbulence, mast, sail interaction, sail.

(35) 2.6. CONCLUSION. 19. planform and cloth (elasticity), heading, sail camber and twist, etc. In order to quantify the aerodynamic forces and investigating the influence of the aforementioned factors on an specific sailing yacht, prediction performance analysis, aeroelastic studies and optimization techniques must be applied. These three research fields are described next. For further information about “sailing concepts”, the author recommends [11] [9] and [8], from which most of the information of this chapter has been obtained..

(36) 20. CHAPTER 2. SAILING CONCEPTS.

(37) Chapter 3 LITERATURE REVIEW The research on sail aerodynamics can be divided in three main fields: performance prediction (section 3.1), aeroelastic analysis (section 3.2) and optimization approaches (section 3.3). Each field studies the same physical problem with a different point of view. In this chapter, the state of the art in these investigations is presented. Applied methods such as wind tunnel tests, full-scale tests and numerical simulations, are described. Performance Prediction Programs (VPP) and Fluid-Structure Interaction (FSI) programs are also explained.. 3.1. Performance Prediction. When designing a sailing yacht, the main objective is finding the optimal aerodynamic performance to beat the hydrodynamic features of the yacht and sail as fast as possible. A Velocity Prediction Program (VPP) is one of the most important tools in this field. These computer codes predict speed, heel angle, leeway angle and many other parameters under different wind conditions. The first VPP was developed by Kerwin in the mid 70’s for the International Measurement System (IMS) handicapping formula [14]. VPPs are used for predicting the performance of a sailing boat by balancing the aerodynamic and hydrodynamic forces and moments so that the vessel sails in equilibrium. This occurs, as explained in [11], when the forces and moments in each of the three directions cancel each other: driving force/hydrodynamic resistance; aerodynamic side force/hydrodynamic side force; vertical force/buoyancy; heeling moment/righting moment; pitching moment/restoring moment; and aerodynamic yawing moment/hydrodynamic yawing moment (see section 2.2). Both aerodynamic and hydrodynamic forces and moments are calculated from coefficients for each condition. The program runs through a set of given true wind speeds and for each speed, a set of wind directions. The result of the VPP is often presented in the form of a polar plot. 21.

(38) 22. CHAPTER 3. LITERATURE REVIEW. Each curve represents the boat speed for a constant true wind speed. Traditional VPPs are based on a steady-state equilibrium between aero- and hydrodynamic forces. But, in the last decade, there have been several investigations to include the dynamic behavior of the yacht. These programs are now called DVPP (Dynamic Velocity Prediction Programs). These can include unsteady conditions due to seakeeping and maneuvering. For example, in 2002, Day et al.[15] developed a tool for time-domain simulation of yacht performance in waves. In 2008, Binns et al.[16] presented a velocity prediction program which was used to simulate the steady state force balance based on towing tank and wind tunnel experiments. Then, they considered the dynamic terms of the equations by systematic series of full scale tests. Another development in VPPs, apart from the dynamic consideration, is the depowering technique. The traditional method uses the trim parameters “reef” and “flat” as introduced by Kerwin [14] to model the depowering. More recently, a third trim parameter named “twist” was introduced by Jackson [17]. Nowadays, the depowering is obtained from wind tunnel tests such as in [18], [19] and [20]. Instead of considering the force coefficients as curves, they can be treated as surfaces where the influence of trim parameters are included. It can be stated that the most important part of a VPP is the quality of the force and moment coefficients. According to [18], prior to the 2000 America’s Cup, many, if not most VPP’s used upwind and downwind aerodynamic models that were essentially similar to the approach first developed by Kerwin [14]. Nowadays a good VPP has the aerodynamic force and moment coefficients of the specific boat in study. These coefficients can be determined in several ways: wind tunnel tests, full-scale measurements and numerical simulations. Which tool or combination of techniques is used depends on the particular case and, of course, the resources available.. 3.1.1. Wind Tunnel Tests. Wind tunnel tests are carried out not only to obtain the aerodynamic coefficients but to have a real-time aerial view of the flying shape of sails. Forces are usually measured with a 6-component balance located below or inside the model. Furthermore, smoke can be used to efficiently visualize the streamlines. The flexible scaled sails can be trimmed remotely. Therefore, the change of forces and streamlines with the sail trim can be acquire immediately. In most of the wind tunnels where sail aerodynamics is investigated, special devices allow the flying shapes to be detected. Thus, forces and flying shapes are recorded simultaneously. The first wind tunnel testing of sailing yacht rigs were performed in the late 1950’s at the Southampton University. The work of the Yacht Research Group and Tony Marchaj [9] has been continued by the Wolfson Unit for Marine Technology. While the wind.

(39) 3.1. PERFORMANCE PREDICTION. 23. tunnel used for the first tests has remained substantially the same, measuring devices and techniques have been gradually refined. Although the general set-up of a wind tunnel has remained substantially the same since the first tests, there was an important development in the mid 90’s when the concept of twisted flow wind tunnel (TFWT) was introduced. It was originally developed by Flay [21] for the New Zealand America’s Cup Challenge in 1995 at the University of Auckland. The TFWT is unique in that it was developed specifically for the testing of yacht sails. This facility can reproduce the twisted flow generated by the true wind profile and the boat speed. More recently, other wind tunnels have incorporated the flow twisting concept, including the Politecnico di Milano in Italy and the University Applied Science Kiel in Germany. Advantages and drawbacks The main advantage of the wind tunnel testing is that the trimming process is similar in the wind tunnel and full-scale since flexible sails are used on the model. Model-scale sails are trimmed remotely and the aerodynamic forces are displayed to the operator in real-time. When the optimum trim is achieved, the aerodynamic forces are recorded. This procedure allows different trims to be investigated easily. Wind tunnel testing is also a cost effective tool comparing to full-scale tests and it is much less time consuming. Moreover, wind tunnel measurements have a good repeatability thanks to the steady and controllable test environment. These advantages make this tool useful in early stages of the design process. The fundamental disadvantage of wind tunnel testing is the inaccurate extrapolation from model scale to full scale values. Results are not completely reliable due to the difficulty of simulating the elasticity of the sails and rigging. To overcome this problem some investigations have been conducted with rigid scaled sails which reproduce the flying shape. There is a good insight of the phenomena involved in the flow around sails and rigging but the trimming process is withdrawn. Recent Investigations Next, it is presented a list of some of the latest publications related to sail aerodynamic research in which wind tunnel tests are conducted.. • Lasher et al. [22] built twelve parametric spinnaker models and tested them in a wind tunnel. In these models, five sail shape parameters were varied (cross-section camber ratio, sail aspect ratio, sweep, vertical distribution of camber, and vertical distribution of sail width). Lift and drag forces were measured for a range of angles of attack and the results were analyzed for three points of sail..

(40) 24. CHAPTER 3. LITERATURE REVIEW. • A symmetrical spinnaker was also tested in [23] for the validation of a fluid-structure interaction program. The model was tested in the Kiel’s Twisted Flow Wind Tunnel (TFWT). • In 2008, Fossati et al. [24] presented an experimental database to provide the scientific community for numerical simulation benchmarking activities, concerning upwind sail aerodynamics. They included some results concerning the relationship between upwind flying shapes and the aerodynamic performance at different apparent wind angles and sail trim settings. The tests were performed in the Politecnico di Milano Twisted Flow Wind Tunnel using a typical IMS cruiser-racer 1/10th scaled model. • Most DVPPs use aerodynamic forces which are calculated from quasi-steady theory. The paper of Gerhardt et al.[25] discusses whether this assumption of quasi-steady aerodynamics can be justified and also analyzes the error introduced by such quasisteady analysis. In order to validate the unsteady potential flow theory for a thin sail-like aerofoil, experiments with an oscillating 2D mainsail model were carried out in the University of Auckland’s Twisted Flow Wind Tunnel. The researchers conclude that if the performance of the yacht is to be predicted on a time-scale shorter than the pitching period, this can be achieved better with an unsteady aerodynamic model rather than with a quasi-steady model. • There are also some recent DVPPs which allow studying the behavior of a yacht while tacking. The aerodynamic models used in these codes usually suffer from a lack of available data on the behavior of the sail forces at very low apparent wind angles where the sails are flogging. In [26] measured aerodynamic force and moment coefficients for apparent wind angles between 0 degrees and 30 degrees are presented. Tests were carried out in the University of Auckland’s Twisted Flow Wind Tunnel in a quasi-steady manner for stepwise changes of the apparent wind angle. • Fossati et al. [27] characterize the aerodynamic behaviour of a 48’ yacht rig scale model by means of experimental tests in the Politecnico di Milano Twisted Flow Wind Tunnel. The experiments allowed to characterize the aerodynamic forces and to study the aeroelastic behaviour of the sailplan. • More recently, Viola et al. [28] presented a paper to provide a benchmark set of pressure distributions for the validation of numerical codes. Modern upwind sails were built at 1/15th -scale and tested in the Twisted Flow Wind Tunnel at Yacht Research Unit (University of Auckland). In chapter 4 more information related to wind tunnel testing is included..