The use of numerical simulation to solve fluid flows and other physical problems has significantly increased during the last decade. This growth is largely a result of improved software user interfaces, more efficient pre- and post-processing tools, and exponentially growing computer horsepower. While the use of Computational Fluid Dynamics (CFD) in the aerospace field has been common place for quite a while, the routine application of CFD to marine related problems has only recently become relatively common place with application to naval, offshore, and America’s Cup sailboat problems leading the way. In the last few years, growing application of CFD to problems facing high speed motor yachts has grown to include:

• Calm Water Resistance
• Added resistance in waves
• Dynamic Stability
• Propulsion
• Seakeeping
• Maneuvering

The most common CFD software applicable to these classes of problems for high speed yachts is based upon the Reynolds Averaged Navier-Stokes equations (RANS). All CFD is based upon varying levels of approximating the Navier-Stokes (NS) equations that are applicable to water and most air flows. The approximation of the NS equations by the RANS equations introduces the necessity for turbulence modeling. Research into improving turbulence modeling continues but suffice it to say that no particular turbulence model allows the accurate prediction of broad classes of real flows. This issue and the impact of gridding on CFD results continue to reduce the fidelity of, and confidence in, CFD results. In spite of these challenges, CFD is a necessary component of a comprehensive design and analysis strategy, best applied in concert with, rather than in isolation of, appropriate experimental studies.

The chief advantages of CFD include:

• Ability to determine results at every point in the flowfield as a natural part of the computation rather than the fairly limited information that is commonly available from experimental results such as integrated properties like lift and drag, pressure at limited number of points on the surface, or flow properties surveyed at a very limited number of points in the flowfield.
• Flows can be solved at full-scale that allows avoiding issues of mismatched similarity parameters (like only being able to match Froude or Reynolds number in tow tank experiments)
• Boundary conditions are more easily matched and flows must not be bounded by the physical constraints of experimental facility. This offers promise of higher fidelity results and avoids having to perform cumbersome blockage corrections to experimental results.

The staff at DLBA includes hydrodynamicists, aerodynamicists and CFD experts who are experienced in the design and application of CFD studies to the design of marine vehicles and routinely utilize this important tool as part of a comprehensive design and analysis strategy as appropriate for each project.