Control surfaces, such as airplane elevators or rudders may use symmetric airfoil shapes which are mostly based on single airfoil geometry. For the 2013 America's Cup sailboat competition rigid sails were specified, based on tandem symmetrical airfoils of equal chord. Because of the unique geometry of this combination and because none of the traditional two-element airfoils were designed for this application, a more suitable airfoil shape was sought. Furthermore, control surfaces such as the rudder are not designed for high lift, while the rigid sail studied here is expected to operate near a lift coefficient of one. A parametric study, using numerical methods, on the effect of different geometrical variables led to the development of an improved sail geometry, compared with the initial baseline shape. Therefore, the first objective of the present study is to validate those predictions for this particular application. Because of the large dimensions of the actual sail, its operating Reynolds numbers are high compared with the available wind tunnel facility. The conservative approach in this study is based on the assumption that the smaller Reynolds number tests provide a satisfactory validation for the higher Reynolds number sailing conditions.
Authors: Giovanni Lombardi (Cubit), Joseph Katz (San Diego State University), Maurizio Foresta (Università di Pisa)
Most sailboats use flexible sails to generate the aerodynamic propulsive force. However, for the 2013 America's Cup sailboat competition, rigid sails were specified. These sails resemble an airplane's wing and traditional wing-design tools (computational and experimental) were used to study the performance of the multi-element sail system. The shape of the proposed sail is based on two, tandem, symmetric airfoils, resulting in a geometry, unlike any traditional two-element airfoil. Because racing regulations limit the sail shape, only the two-dimensional airfoil geometry was open for a redesign. Therefore, the first objective of this study was to identify the possible variables affecting the aerodynamic performance of such sails (within the framework of racing regulations). At the same time, a secondary objective was to evaluate the effectiveness of simple computational and experimental tools for such a design exercise.
Authors: Giovanni Lombardi (Cubit), Joseph Katz (San Diego State University), Maurizio Foresta (Università di Pisa)
Keywords: rigid sail, America's Cup, aerodynamics, multi-element airfoil, sailboat racing
Transactions of the Royal Institution of Naval Architects part B, 155(part B1), B13-B24, International Journal of Small Craft Technology, 138
Le applicazioni della Computational Fluid Dynamics (CFD) in ambito nautico hanno raggiunto un elevato livello di maturità, consentendo l'analisi integrata delle prestazioni, della stabilità e del comportamento dinamico di imbarcazioni ad alte prestazioni in condizioni di mare reale.
L'impiego di modelli non stazionari con superficie libera e moto rigido a sei gradi di libertà permette di simulare in modo realistico l'interazione tra aerodinamica delle parti emerse, idrodinamica dello scafo e risposta dinamica del sistema. Le procedure CFD risultano particolarmente efficaci sia nelle attività di ottimizzazione di componenti specifici, come derive e bulbi, sia nella valutazione delle prestazioni globali di configurazioni complete, inclusi yacht da competizione e catamarani veloci.
Le simulazioni forniscono informazioni quantitative su velocità, assetto, accelerazioni, carichi e frequenze dominanti del moto, difficilmente ottenibili con sole prove sperimentali. Nonostante gli elevati costi computazionali, l'uso di infrastrutture HPC rende la CFD uno strumento chiave nel processo di progettazione e validazione in ambito navale.
Conference/Journal: La Simulazione Fluidodinamica: Stato dell'Arte nelle Applicazioni Marine, UNIGE, 2013
Authors: G. Lombardi
Keywords: CFD nautico, idrodinamica, yacht, catamarano, ottimizzazione, superficie libera, HPC
La Simulazione Fluidodinamica: Stato dell’Arte nelle Applicazioni Marine, UNIGE
The evolution of computational resources has been a key enabler for the progressive integration of Computational Fluid Dynamics (CFD) into aerodynamics analysis and design. From early potential-flow solvers running on mainframe systems to modern high-performance computing (HPC) clusters, increasing computational power has allowed the transition toward large-scale RANS simulations, unsteady flow analysis, thermo-aerodynamics, optimization procedures, and fluid-structure interaction.
The availability of parallel architectures and fast networks has significantly reduced turnaround times while enabling the use of finer grids and more realistic geometries. This evolution has strengthened the synergy between CFD and experimental testing, positioning numerical simulation as a central tool in industrial design processes, particularly in automotive, naval, and aerospace applications.
Current trends toward massively parallel systems, GPU acceleration, and reduced memory per core highlight the need for new software paradigms and methodologies to further improve efficiency, accuracy, and predictive capability in future CFD-driven design workflows.
Conference/Journal: 2nd Future Automotive AeroDynamics Conference, Berlin (DE), 2013
In modern automotive design, aerodynamics plays a central role and is strongly coupled with styling, structural constraints, cooling requirements, and vehicle dynamics. This paper discusses the role, potential, and critical issues of numerical optimization techniques applied to car aerodynamics, with particular emphasis on CFD-based approaches.
The continuous growth of computational power has enabled the integration of automated optimization procedures into the aerodynamic development process, allowing the systematic exploration of large design spaces and the evaluation of thousands of geometrical configurations.
The basic principles of aerodynamic optimization are outlined, from the definition of cost functions and constraints to mesh generation and solver coupling. Examples of industrial-oriented applications are presented, showing how optimization can support the designer in improving performance, reducing drag, and enhancing flow control solutions. At the same time, the paper highlights the main limitations of current methodologies, including computational cost, robustness, and the difficulty of managing complex real-world constraints.
Conference/Journal: Future Automotive AeroDynamics Conference, Berlin (DE), 2012
Authors: G. Lombardi
Keywords: numerical optimization, car aerodynamics, CFD-based design, drag reduction, automotive development
Future Automotive AeroDynamics Conference, Berlin (DE)
High-speed catamaran design requires accurate prediction of performance and dynamic behavior under both calm and rough sea conditions. Advanced CFD techniques enable the simultaneous analysis of hydrodynamics, aerodynamics, and vessel motion, providing detailed insight into stability, loads, and propulsion efficiency.
A fully unsteady numerical approach with free-surface modeling and six-degrees-of-freedom rigid body motion allows realistic simulation of hull dynamics in waves. Sensitivity analyses on grid resolution highlight the trade-off between computational cost and solution accuracy, while refined meshes improve the representation of wave-hull interaction.
The numerical results provide quantitative information on speed, trim, accelerations, dominant motion frequencies, and the influence of weight and inertial properties. Simulations in rough sea conditions show modified oscillation amplitudes and frequencies, while preserving harmonic motion characteristics. The methodology demonstrates the capability of CFD to support the design and optimization of high-performance marine platforms.
Conference/Journal: STAR European Conference, London, 2010
Alessandro Mariotti, Giovanni Lombardi, Marco Maganzi
2010
Cubit, Università di Pisa
Abstract
Advanced CFD techniques make it possible to investigate the complex interaction between aerodynamics, hydrodynamics, and rigid-body motion in sailing yachts operating in realistic sea conditions. Free-motion simulations that couple unsteady multiphase flow models with six-degree-of-freedom dynamics enable the evaluation of yacht performance in up-wind sailing under rough sea states. This integrated approach combines turbulence modeling, volume-of-fluid wave representation, and dynamic mesh handling to capture both sail aerodynamics and hull–wave interactions. The methodology allows detailed analysis of boat motions, thrust generation, hydrodynamic loads, and their correlations with velocity, heel, and pitch, providing insight into off-design behavior that cannot be obtained from simplified or steady configurations. Although computationally demanding, such simulations offer a powerful tool to support yacht design and performance assessment, improving the understanding of real operating conditions and enabling more informed engineering choices in high-performance sailing applications.
Authors: G. Lombardi, M. Maganzi, A. Mariotti
Conference/Journal: STAR European Conference, London, 2010
Enrico Cardile, Ferdinando Cannizzo, Giovanni Lombardi, Marco Maganzi
2010
Cubit, Ferrari, Università di Pisa
Abstract
Un'analisi aerodinamica che consideri gli effetti di tutti i parametri potrebbe sembrare difficile. Nell'analisi tramite ottimizzazione numerica un codice aerodinamico è accoppiato ad una routine di ottimizzazione per gestire automaticamente i valori delle variabili di progetto, con l'obiettivo di minimizzare una funzione obiettivo assegnata. Questo approccio è estremamente flessibile ed in grado di rispondere ad esigenze multidisciplinari.
Il progetto ha dimostrato l'applicabilità delle procedure di ottimizzazione nel contesto del settore automobilistico, utilizzando un codice CFD per l'aerodinamica. L'integrazione dell'ottimizzazione aerodinamica in fase di progettazione permette ai progettisti di interagire velocemente con gli altri gruppi. Diventa possibile cercare soluzioni che garantiscano le prestazioni cercate, che non influenzino negativamente lo stile dell'auto, e che al contempo diano un elevato grado di efficienza e sicurezza.
Enrico Cardile, Ferdinando Cannizzo, Giovanni Lombardi, Marco Maganzi
2010
Cubit, Ferrari, Università di Pisa
Abstract
Il comfort termico in abitacolo rappresenta un aspetto sempre più rilevante nella progettazione automobilistica ad alte prestazioni, risultando dall'interazione complessa tra fenomeni termo-fluidodinamici e percezioni fisiologiche soggettive.
Viene presentata una procedura integrata per la valutazione del comfort termico basata su simulazioni CFD, finalizzata alla definizione di indici quantitativi rappresentativi delle condizioni ambientali interne al veicolo. L'approccio combina l'analisi del campo di velocità, temperatura, umidità e irraggiamento con modelli di bilancio termico del corpo umano, introducendo un indice globale di comfort ottenuto dalla ponderazione di contributi locali legati a equilibrio termico, raffiche, gradienti verticali e laterali di temperatura.
Le simulazioni includono flussi freddi e caldi, meccanismi di conduzione, convezione e irraggiamento solare, su geometrie realistiche di abitacolo. La procedura è validata mediante prove sperimentali in galleria climatica e test soggettivi, mostrando una buona correlazione tra risultati numerici e dati sperimentali.
David Nuri, Ferdinando Cannizzo, Giovanni Lombardi
2010
Cubit, Ferrari, Università di Pisa
Abstract
The rear diffuser represents an important tool to increase the vertical load of a high-performance car. In order to improve its effectiveness, a solution based on flow blowing is considered. Different geometrical scheme of the blowing were considered. To make a corrected comparison between the different solutions, an optimisation procedure were applied to each geometrical scheme. Coarse tetrahedral grids are used during the optimisation process, while a final verification with a very refined grid is presented to validate the results. More than 2500 different configurations are analysed, spending one month on a 16 nodes linux cluster. Final results show that important increase in the down-force, without drag penalization, can be obtained by using flow-blowing devices.
Authors: Giovanni Lombardi, Nuri David, Ferdinando Cannizzo, Enrico Cardile
Conference/Journal: 8th MIRA International Vehicle Aerodynamics Conference, Oxford (GB)
