Mixture Multiphase (MMP) Model Reference

In cases where the mixture of phases can accurately represent the quantities of the individual phases, the Mixture Multiphase (MMP) model can be used as an alternative to more numerically expensive Eulerian Multiphase (EMP) simulations. You can model resolved free surfaces and unresolved mixtures, and include both mixtures and free surface flows in the same simulation.

To model the interface between phases, when such an interface exists, Mixture Multiphase (MMP) uses the large scale interface detection model that is implemented within the Eulerian Multiphase (EMP) multiple flow regime framework. This model determines the group of cells that contain a large interface.

Mixture Multiphase (MMP) Properties

Convection

Sets the discretization scheme that Simcenter STAR-CCM+ uses for computing the convection flux on a cell face in appropriate transport equations.

Method	Corresponding Method Nodes
1st-Order First-order upwind scheme. Only use when a higher-order scheme fails to give convergence, or in order to obtain an initial solution before switching to a higher-order scheme.	None.
2nd-Order Second-order upwind scheme. Using this scheme can lead to poorer convergence properties, but gives accuracy as good as or better than the first-order scheme.	None.
Adaptive Interface Sharpening Adaptive Interface Sharpening (ADIS) convection scheme for Mixture Multiphase (MMP). This method models the interface between phases, when such an interface exists. The ADIS scheme adaptively blends an interface sharpening scheme (the High Resolution Interface Capturing (HRIC) scheme) and a Total Variation Diminishing (TVD) scheme (the first order or second order scheme). Using this option is appropriate in cases where sharp interfaces and dispersed mixtures co-exist between the same pair of phases. It is also useful in cases where the interface between the phases becomes large, or when the interface enters a region where the numerical mesh is sufficiently fine to resolve the interface. See Adaptive Interface Sharpening (ADIS) Scheme for Volume Fraction.	Adaptive Interface Sharpening The following properties are available: Angle Factor The angle factor $C_{\theta }$ in the HRIC convection discretization scheme for interface tracking. If the free surface is not smooth and not following the grid lines, increase its value. CFL_l The lower Courant number limit in the HRIC convection discretization scheme. This value is ${Co}_l$ in Eqn. (2594). CFL_u The upper Courant number limit in the HRIC convection discretization scheme. This value is ${Co}_u$ in Eqn. (2594). Use Second Order TVD When this option is deactivated, the first order scheme is used as the Total Variation Diminishing (TVD) scheme in blending. Number of Cell Layers for Smoothing Specifies the number of cells across which the blending function is smoothed from the Large Interface Marker Band. See $n_s$ in Eqn. (2316). The default value is 3 cells. Large-Scale Interface Detection Enables the detection of large interface cells and the calculation of the interfacial distance in those cells. See Large Scale Interface Detection.

Face Density Reconstruction

Sets the discretization scheme to reconstruct density at internal faces.

Method	Corresponding Method Nodes
1st-Order Uses first order face density reconstruction. This discretization scheme is computationally cheaper, but less precise. For simulations where a high level of consistency between different transport equations is less important, this option can be used to reduce the simulation time.	None.
2nd-Order Uses second order face density reconstruction. This discretization scheme is computationally more expensive, but offers a high level of consistency between all transport equations. This option is the default selection and should be used for compressible simulations (that is, if the Mach number exceeds about 0.3).	None.

二阶梯度

Simcenter STAR-CCM+ 流动求解器中有两个二阶梯度源：

• 用于扩散的边界二阶梯度
• 网格单元面上用于扩散的内部二阶梯度

使用此属性可控制求解器中要包括哪些梯度。打开时将提供两种梯度，关闭时排除这两种梯度。选择仅限内部和仅限边界时，将选择相应的梯度。

流体边界扩散

激活时，此属性将包括如 Eqn. (899) 所给定的流体边界扩散通量（或流模型的粘性通量）。默认情况下，此属性已激活。

Models

When the Mixture Multiphase (MMP) model is activated, the following model becomes available in the physics continuum:

Porous Media

This model represents a porous material as a solid phase. Use it to model the physical velocity inside a porous medium instead of the superficial velocity, or when solid and fluid inside porous media are not in thermal equilibrium.

See Porous Media Models.

Film-MMP Phase Interaction

This model is selected automatically when you create a phase interaction with a Fluid Film phase and an MMP phase. The following phase interaction models are available:

Incident Mass Flux Impingement

Calculates the mass flux of the droplets that impinge on the wall to form a fluid film. You specify the impingement efficiency, that is, the fraction of the total mass impinging on the fluid film boundary that is transferred from the MMP phase into the fluid film.

See Incident Mass Flux Impingement.

Stripping

Models the transfer of mass due to droplets stripping from the fluid film to the corresponding MMP phase. You specify the stripping methods to model: edge stripping, wave stripping, or both. Edge film stripping models the ejection of droplets from the fluid film when it flows over a sharp edge. Wave film stripping models the ejection of droplets from the fluid film as a result of wave-induced instabilities.

See Edge Stripping and Wave Stripping.

Materials and Methods

Dynamic Viscosity

The dynamic (shear) viscosity of the fluid mixture is a measure of its resistance to shearing flows. The value that you set here is ${\mu }_m$ in the formulation.

Computed using the Volume-Weighted Mixture method.

Activated when the Laminar model or Turbulent model is selected in the Viscous Regime.

Specific Heat

The specific heat of the fluid mixture is the ratio of the heat added to the mixture and the resulting temperature change. This value is $C_p$ in the formulation. Computed using the Mass-Weighted Mixture method.

Activated when an energy model is selected in the physics continuum.

See Segregated Multiphase Temperature Model Reference.

Thermal Conductivity

The thermal conductivity of the fluid mixture is a measure of the ability of the mixture to conduct heat. This value is $\lambda$ in the formulation. Computed using the Volume-Weighted Mixture method.

Activated when an energy model is selected in the physics continuum.

Turbulent Schmidt Number

The Turbulent Schmidt Number is used to characterize turbulent fluid flows in which there are simultaneous momentum and mass diffusion convection processes. The value that you set here is ${\sigma }_t$ in Eqn. (2875).

Activated when the Turbulent model is selected in the Viscous Regime.

Boundary Settings

Inflow Boundaries

Velocity

When the Slip Velocity model is activated, the phase velocities at the inlet boundary are extrapolated consistently from the interior domain. In this scenario, there is no direct control over the velocity of the individual phases.

Volume Fraction

The ratio of the volume that each phase occupies to the computational cell volume.

When you specify boundary values, there is no restriction on the values that you can set for the volume fractions of the phases. However, Simcenter STAR-CCM+ uses normalized values for each phase volume fraction to ensure that the total volume fraction is 1.0.

Pressure Outlet

Volume Fraction

The ratio of the volume that each phase occupies to the computational cell volume.

• This setting is relevant only if backflow occurs. If you do not have backflow, ignore this setting.

• If you have backflow, and only one phase is present at the pressure outlet, set the volume fraction of that phase to 1.

• If you have backflow, and a mixture of phases is present at the outlet, it is unlikely that the pressure outlet correctly captures your physics. (A pressure outlet assumes a constant pressure across the outflow interface.) You are advised to move the outlet further downstream and bring any outlet pipes back to the horizontal orientation so that backflow no longer occurs.

Region Settings

The following setting applies to each phase and also applies to each fluid region.

Each phase momentum source is added to the region (the fluid mixture) momentum source (see Eqn. (2877)). The phase momentum sources are also taken into account, along with the gravity force and inertial force, when calculating the Drag-Based Slip Velocity (see Eqn. (2895)).

Momentum Source Option

Method	Corresponding Physics Value Nodes
None Specified Adds a specified momentum source to the momentum equation.	When the Specified method is selected: Momentum Source Momentum Source Velocity Derivative See Momentum Source Option.

The following settings apply to fluid regions.

Initial Condition Option

Lets you customize initial conditions for an individual region.

See Setting Initial Conditions for a Particular Region.

Turbulence Source Option

Available when a turbulence model is activated in the physics continuum.

Method

Corresponding Physics Value Nodes

Turbulence Source Option None Specified Ambient

When the Specified method is selected: Specific Dissipation Rate Source Available for the K-Omega turbulence model. See K-Omega Regions Reference. Turbulent Kinetic Energy Source Available for both the K-Omega and K-Epsilon turbulence models. Turbulent Dissipation Rate Source Available for the K-Epsilon turbulence model. Turbulent Dissipation Rate Source Derivative Available for the K-Epsilon turbulence model. Turbulent Kinetic Energy Source Derivative Available for the K-Epsilon turbulence model. See K-Epsilon Regions Reference. When the Ambient method is selected: Ambient Turbulence Specification

Volume Fraction Source Option

Method	Corresponding Physics Value Nodes
Phase Source Term When activated, user-specified volume fraction sources are enabled.	Volume Fraction Sources Volume Fraction Sources Pressure Derivative Volume Fraction Sources Volume Fraction Derivative

Field Functions

When the Mixture Multiphase (MMP) model is activated, the following field functions become available:

Absolute Total Pressure of [phase]

The pressure that results from isentropically bringing the flow to rest in the absolute frame of motion, defined as $P_{t,abs}^i=p_{t,i}+p_{ref}$ , where $p_{t,i}$ and $p_{ref}$ are the Total Pressure and the Reference Pressure for each phase.

Total Pressure of [phase]

The absolute total pressure minus the reference pressure defined. The total pressure is specified per phase.

For incompressible fluid:

$$p_{\text{t,i}}=p+\frac{1}{2}{\rho }_i{v_{rel,i}}^2$$

For compressible fluid:

$$H_{t,rel}^i=H(T_0,p_{t,i})$$

and

$$s(T_0,p_{t,i})=s(T,p)$$

where

• $p$ is the mixture pressure
• ${\rho }_i$ is the density of the phase i
• ${\text{v}}_{rel,i}$ is the relative velocity of phase i
• $H_{t,rel}^i$ relative total enthalpy of phase i
• $H(T,p)$ enthalpy at temperature T and pressure p
• $s(T,p)$ entropy at temperature T and pressure p and pressure.

Total Temperature of [phase]

The temperature that is obtained from bringing the fluid to rest. The total temperature is specified per phase, using the equation of state of the phase under consideration.

For incompressible fluid:

$$H_{t,rel}^i=H(T_{\mathrm{t},i},p_{t,i})$$

For compressible fluid:

$$H_{t,rel}^i=H(T_{\mathrm{t},i},p_0)$$

and

$$s\left(T_{t,i}{,p}_0\right)=s(T,p)$$

where

• $T$ is the mixture temperature
• $T_{t,i}$ relative total temperature of phase i
• $H_{t,rel}^i$ relative total enthalpy of phase i

Mass Flow Rate of [phase]

The mass of a particular phase per unit time $kg/s$ flowing through the boundary face. The convention is such that positive mass flow rate means outflow.

Mass Flux of [phase]

The mass of a particular phase per time per area flowing through the boundary face. This value is oriented such that positive mass flux means inflow.

Mass Imbalance of [phase]

The imbalance of mass in any cell, which is defined as $\sum _f{\dot{m}}_f$ for each cell.

Velocity Divergence Imbalance

The imbalance of volume fluxes, equivalent to the mass imbalance for mass-flux based models.