Trans RINA, Vol 153, Part B2, Intl J Small Craft Tech, 2011 Jul-Dec
parameters. These models are crude representations of the real forces acting on sailing yachts [11-15]. Some of their drawbacks are known to result in some misleading predictions but increasing their performance is not easy [11-15]. As said before by Korpus [16], experiments are probably the best method to predict these forces by taking into account
illustrate capabilities of the computational framework ADONF for sail design and optimization with an FSI formulation for three-dimensional flows.
2. real world effects like viscous
separation, unsteadiness, etc… However, it is difficult to discard scale effects during the transposition to real yachts. In that direction, full-scale measurements have been recently performed [17]. It is always difficult to take into account aero-structural coupling which is one of the main factors in sail design. Another difficulty specific to experiments is the ability to access all physical variables needed to better understand flow around bodies which may be helpful to guide future design.
The best aerodynamic model we have today is viscous CFD through RANS simulations [16, 18-23]. RANS codes have two drawbacks when used to predict forces acting on a yacht. They may be time-consuming and they need some expertise to be accurate. However, the greatest time consuming task in the process is the engineer time needed to generate meshes with a high quality standard on complex geometries. These facts drive two questions to make RANS methods useful for yacht and sail designers:
These
Is it possible to automate mesh generation and integrate RANS simulations into a friendly environment?
user-
Is it possible to validate RANS predictions by comparisons with experiments representative to real flow conditions?
papers [21,
questions have 22]
by
been addressed in previous developing a computational
framework ADONF for two-dimensional aerodynamic problems. It has been shown that it is possible to resolve the optimization problem about sail design and sail interactions by simulating a large number of flow configurations
through high-fidelity RANS solver.
Examples illustrated have been focused on questions like: how to better design and trim interacting sails, or complex rigs? How to maximize a given function like driving force
chosen to evaluate In this paper the the sailing boat
performance and taking into account some constraints like the maximum heeling moment?
framework ADONF is
extension of the computational proposed to address
dimensional FSI problem. The
fluid model is briefly presented in its main
components and key elements for accurate results. The structural model is described with special attention to the fluid structure interfacing methods computational
used. The framework and the optimization algorithm are also described. Then examples are used to three-
In this section, main elements of the computational model are described. Fluid dynamics equations used to simulate the flow around interacting sails are presented with the solver and physical models and limitations. RANS equations have been resolved on hybrid meshes with structured and unstructured mesh and conformal or non-conformal interfaces between domains [19]. The hybrid mesh strategy is a powerful technology which increases flexibility to generate high quality meshes around interacting sails for two and three-dimensional flows [19].
2.1 SOLVER
The solver used for the resolution of the Navier-Stokes equations in most of the paper is Fluent 6.3 except in section 7.5 where OpenFOAM 1.6 is used. FLUENT is a steady or unsteady, compressible or incompressible, three-dimensional solver which resolves the previously given RANS equations. In the
present study, the
incompressible version with segregated solver and the Spalart-Allmaras turbulence model [24] with standard constants have been used. Second-order spatial schemes were used and second-order temporal schemes were used for unsteady
simulations. The usefulness of
second-order scheme will be illustrated in the result section.
To solve the Navier-Stokes equations, proper boundary conditions are required on all frontiers of the flow domain. At the wall boundaries, the no-slip condition is applied. A pressure outlet boundary condition is applied at the outlet. A symmetry boundary condition is used on the top and bottom faces of the domain. A velocity inlet boundary condition is applied on other frontiers (inlet, leeward and windward) with a background turbulence level simulations,
of a 1%. MESH ISSUES uniform wind
For Three-dimensional without
atmospheric
boundary layer profile is used for the inlet condition. 2.2
The mesh generation is a crucial step in the process of RANS simulation. It is a time consuming activity which needs engineer experience and long practice to rigorously clean the CAD geometry and to make the best choice for the mesh topology and generation. The mesh influence on the
configurations may be important
results on typical sails and
should be
carefully evaluated and bounded by relevant choices in mesh size and distribution over the flow domain. Boundary layers have to be resolved on bodies (mast and sails) and this imposes some criteria on mesh size
FLUID MODEL
B-104
©2011: The Royal Institution of Naval Architects
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