Several of the interfaces vary only by one or two default settings (see Table 6-1, Table 6-2, Table 6-4, and Table 6-5) in the Physical Model and Turbulence sections, which are selected either from a check box or a list. For the Multiphase Flow branch, the Bubbly Flow (bf), Mixture Model (mm), Euler-Euler Model (ee), and Phase Transport subbranches have several physics interfaces each depending on the turbulence model used. All the Two-Phase Flow interfaces contain a multiphysics coupling feature with a name as (tpf). The Three-Phase Flow, Phase Field branch contains a single interface for laminar flow.

The Bubbly Flow () branch interfaces are used primarily to model two-phase flow where the fluids are gas-liquid mixtures, and the gas content is less than 10%. The Laminar Bubbly Flow Interface () solves the Navier–Stokes equations with the momentum equation corrected by a term induced by the slip velocity. The slip velocity can be described by the Hadamard–Rybczynski drag law for small spherical bubbles, a nonlinear drag law taking surface tension into account for larger bubbles, or by defining it on your own.

The various forms of the Bubbly Flow, Turbulent Flow interfaces () solve the RANS equations for the filtered velocity field and filtered pressure as well as models for the turbulent viscosity. The Bubbly Flow, Turbulent Flow interfaces include all the turbulence models available in the Single-Phase Flow, Turbulent Flow interfaces. See The Bubbly Flow Interfaces for links to the physics interface information.

The Mixture Model () branch interfaces are similar to the Bubbly Flow interfaces except that both phases are assumed to be incompressible. Examples include solid particles dispersed in a liquid, and liquid droplets dispersed in another liquid when the two liquids are immiscible.

Like the Bubbly Flow interfaces, The Mixture Model, Laminar Flow Interface () and Mixture Model, Turbulent Flow interfaces () solve the flow equations, whether described by the Navier–Stokes equations or the RANS equations with different turbulence models, and where the momentum equation is corrected by a term induced by the slip velocity. The slip velocity can be described by the Hadamard–Rybczynski, Schiller–Naumann or Haider–Levenspiel method, or by defining it on your own.

The Euler-Euler Model () branch interfaces are used to model the flow of two continuous and fully interpenetrating phases. For both phases the conservation equations are averaged over volumes, which are small compared to the computational domain, but large compared to the dispersed phase particles, droplets or bubbles. The Euler-Euler Model, Laminar Flow Interface solves two sets of conservation equations, one for each phase. The Euler-Euler Model, Turbulent Flow Interface additionally solves transport equations for the turbulence quantities, either using a mixture averaged turbulence models or solving separate transport equations for the turbulence quantities of each phase. The drag model for solid particles or liquid droplets/bubbles can be described by the Hadamard–Rybczynski, Schiller–Naumann or Ishii–Zuber, closures, or by defining it on your own. In addition the Haider–Levenspiel and Gidaspow closures are available for solid particles, and the Tomiyama and others closure is available for liquid droplets/bubbles.

The Phase Transport Mixture Model () branch interfaces are similar to the Mixture Model interfaces. The main difference is that the Phase Transport Mixture Model interfaces are multiphysics interfaces that couple a single-phase flow interface with a Phase Transport interface, allowing for multiple dispersed phases.

Like the Mixture Model interfaces, The Phase Transport Mixture Model, Laminar Flow and Turbulent Flow Interfaces solve the flow equations, whether described by the Navier–Stokes equations or the RANS equations with different turbulence models, and where the dispersed phase velocities are determined by the slip velocity. The slip velocity can be described by the Hadamard–Rybczynski, Schiller–Naumann or Haider–Levenspiel closures, or by defining it on your own.

The Laminar Two-Phase Flow, Level Set Interface () and The Turbulent Two-Phase Flow, Level Set Interfaces (), found under the Two-Phase Flow, Level Set branch (), are used primarily to model two fluids separated by a fluid interface. The moving interface is tracked in detail using the level set method. Surface tension acting on the fluid interface can be included in the fluid-flow equations.

The Laminar Two-Phase Flow, Phase Field Interface () and The Turbulent Two-Phase Flow, Phase Field Interfaces () found under the Two-Phase Flow, Phase Field branch (), also model two fluids separated by a fluid interface. You can easily switch between the physics interfaces, which can be useful if you are not sure which physics interface provides the best description. Surface tension acting on the fluid interface are per default included in the fluid-flow equations. Library surface tension coefficients between a number of common substances are also available.

The Two-Phase Thin-Film Flow, Domain, Phase Field Interface (), The Two-Phase Thin-Film Flow, Phase Field Interface for 2D () and The Two-Phase Thin-Film Flow, Phase Field Interface for 3D () found under the Two-Phase Thin-Film Flow, Phase Field branch (), model two fluids separated by a fluid interface, in a narrow channel represented by a domain, edge or surface within the geometry. Surface tension acting on the fluid interface are per default included in the fluid-flow equations. Library surface tension coefficients between a number of common substances are also available.

The Laminar Three-Phase Flow, Phase Field Interface found under the Three-Phase Flow, Phase Field branch () models flows of three incompressible fluids separated by sharp interfaces. Library surface tensions between a number of common substances are also available.

The Laminar Two-Phase Flow, Moving Mesh Interface , () found under the Multiphase Flow>Two-Phase Flow, Moving Mesh branch (), is used primarily to model two fluids separated by a fluid interface. The moving interface is tracked as a boundary condition along a line or surface in the geometry. However, the method cannot accommodate topological changes in the boundary. Surface tension acting on the fluid interface are per default included in the fluid-flow equations. Library surface tension coefficients between a number of common substances are also available.