Multiphase Flow
The Multiphase Flow branch () enables the modeling of multiphase flows. These physics interfaces are included:
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The Laminar Two-Phase Flow, Level Set Interface () (available under the Two-Phase Flow, Level Set branch ()).
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The Laminar Two-Phase Flow, Phase Field Interface () (available under the Two-Phase Flow, Phase Field branch ()).
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The Laminar Three-Phase Flow, Phase Field Interface () (available under the Three-Phase Flow, Phase Field branch())
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The Laminar Two-Phase Flow, Moving Mesh Interface () (available under the Two-Phase Flow, Moving Mesh branch ()).
The Two-Phase Flow interfaces can add surface tension forces (including the Marangoni effect) at the two fluid interface(s). A library of surface tension coefficients between some common substances is available.
For problems involving topological changes (for example, jet breakup), use either the Level Set or Phase Field interfaces. These techniques use an auxiliary function (the level set and phase field functions, respectively) to track the location of the interface, which is necessarily diffuse. The Level Set interface does not include surface tension force per default, and is recommended for use in larger scale problems with larger velocities, or when the effects of the gradient of the surface tension coefficient are relevant. The interface also includes a domain feature for porous domains. The phase field method is physically motivated and is usually more numerically stable than the level set method. It is can also be extended to more phases and is compatible with fluid-structure interactions.
The moving mesh method represents the interface as a boundary condition along a line or surface in the geometry. Because the physical thickness of phase boundaries is usually very small, for most practical meshes The Laminar Two-Phase Flow, Moving Mesh Interface describes the two-phase boundary the most accurately. However, it cannot accommodate topological changes in the boundary.
For all the Two and Three-Phase Flow interfaces, compressible flow is possible to model at speeds of less than 0.3 Mach. You can also choose to model incompressible flow by simplifying the equations to be solved. Stokes’ law is also an option.
In each physics interface, the density and viscosity are specified for both fluids. You can easily use non-Newtonian models for any of the fluids, based on the Power law, Carreau, Bingham-Papanastasiou, Herschel-Bulkley-Papanastasiou, and Casson-Papanastasiou models, or using an arbitrary user-defined expression.
It is often advantageous to use more than one of these techniques to solve a problem — for example, a level set model for jet breakup could be checked prior to breakup by a moving mesh model to ensure that the surface tension is captured accurately by the diffuse interface.
Under the Mathematics>Moving Interface branch () when adding an interface, The Level Set Interface (), The Level Set in Porous Media Interface (), The Phase Field Interface (), and The Ternary Phase Field Interface () are available in a form uncoupled with the equations of flow. These interfaces can be used to model phenomena in which other factors dominate over the fluid flow, such as some forms of phase separation.