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# Why FLOW-3D?

FLOW-3D is a powerful modeling tool that gives engineers valuable insight into many physical flow processes. With special capabilities for accurately predicting free-surface flows, FLOW-3D is the ideal computational fluid dynamics software to use in your design phase as well as in improving production processes.

## Free Gridding Separates Meshing from Geometry Construction

FLOW-3D uses an approach to gridding that combines the advantages of simple rectangular grids with the flexibility of deformed, body-fitted grids. The approach is referred to as "free-gridding" because grids or geometry can be freely changed, each independent of the other. This feature eliminates the tedious task of generating body-fitted or finite-element grids. FLOW-3D uses a fixed grid of rectangular control elements because these are simple to generate and possess many desirable properties (e.g., improved accuracy, smaller demands on memory, and simpler numerical approximations). Read more about FLOW-3D's free-gridding approach in CFD-101 >

## Modeling Fluid Flow in Complex Geometry is Easy with FAVOR™

FLOW-3D incorporates a special technique, known as the FAVOR™ (Fractional Area Volume Obstacle Representation) method, which is used to define general geometric regions within the rectangular grid. The philosophy behind FAVOR™ is that numerical algorithms are based on information consisting of only one pressure, one velocity, one temperature, etc., for each control volume, so it would be inconsistent to use much more information to define the geometry. Thus, the FAVOR™ technique retains the simplicity of rectangular elements while representing complex geometric shapes at a level consistent with the use of averaged flow quantities within each volume element. Read more about FLOW-3D's FAVOR™ technique in CFD-101 >

## TruVOF and Free Surface Modeling

FLOW-3D differs from other computational fluid dynamics software in its treatment of flowing fluid surfaces. The program uses special numerical methods to track the location of surfaces and to apply the proper dynamic boundary conditions at those surfaces. In FLOW-3D, free surfaces are modeled with the Volume of Fluid (VOF) technique that was first developed by a group of scientists, including Flow Science’s founder, Dr. C. W. Hirt, at the Los Alamos National Laboratory. A number of competing CFD programs claim to have incorporated a VOF capability, when in reality they implement only one or two of the three fundamental VOF ingredients. Prospective users of CFD should be aware that these pseudo-VOF schemes will often give incorrect results. FLOW-3D has all of the ingredients recommended for the successful treatment of free surfaces. Moreover, FLOW-3D incorporates major improvements beyond the original VOF method to increase the accuracy of boundary conditions and the tracking of interfaces. We refer to our implementation as TruVOF. Read more about FLOW-3D's TruVOF method in CFD-101 >

## Multi-Block Meshing for Efficiency and Speed

FLOW-3D offers multi-block meshing, which is designed to add even more flexibility and efficiency to the finite difference meshing technique. In a standard finite difference mesh, local refinements may lead to a substantial increase in the total number of cells since mesh lines extend all the way to domain boundaries in all three directions. Use of multiple blocks allows such refinements to be more localized, and therefore requires fewer computer resources. The multi-block feature is especially useful in so-called "rangy" problems, where features exist that are small compared to the overall domain size, like small obstacles and thin channels. Using multiple mesh blocks, a user can "link" individual blocks to mesh a "rangy" domain and mesh only the areas of interest and limit the total number of computational cells. Using a "nested" block, a user can enhance the resolution around an area of interest. Read more about Multi-Block Meshing in FLOW-3D.

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