Volumetric Source Reference

The Volumetric Source time-step provider is appropriate for phase mass transfer from Volume of Fluid (VOF) or Mixture Multiphase (MMP) simulations. This time-step provider adjusts the simulation time-step size based on the phase mass transfer contributions to the source terms of the continuity equation.

The Volumetric Source time-step provider determines a time-step size by comparing the volume which would be created by mass transfer from phase interaction models, such as boiling, evaporation/condensation, impingement/stripping, cavitation, or user defined sources with the volume of the receiving cell. The proposed new time-step size depends on how fast the mass transfer occurs and the volume of the cell which inherits the mass transfer.

The volumetric source time-step provider is available when the Volume of Fluid (VOF) or the Mixture Multiphase (MMP) model is activated in the physics continuum, applicable to mass transfer phase interaction models. This time-step provider is also applicable to user-specified volume fraction sources, for example when the Phase Source Term is activated for the [region] > Physics Conditions > Volume Fraction Source Option. The volumetric source time-step provider determines the time-step size from the use- specified field function for the phase Volume Fraction Sources.

The volumetric source time-step provider estimates the time-step $Δ t$ based on the ratio of the net volumetric continuity source ${\dot{m}}_{V}$ from all the participating phase interaction models to the (cell) volume $V$ that is available to accommodate that transfer rate within one time-step:

Figure 1. EQUATION_DISPLAY

\begin{matrix} ‖ \dot{m_{V}} ‖ \cdot Δ t \leq V & \Leftrightarrow & Δ t \leq \frac{V}{‖ \dot{m_{V}} ‖} \end{matrix}

(106)

The time-step conditions are adjusted (relaxed/tightened) by the user-defined scaling factor

C

as:

Figure 2. EQUATION_DISPLAY

\begin{matrix} Δ t \leq C \frac{V}{‖ \dot{m_{V}} ‖} \end{matrix}

(107)

Table 1. Volumetric Source Reference
Provided By	Right-click Continua > Physics 1 > Models > Adaptive Time-Step > Time-Step Providers and select New > Volumetric Source
Example Node Path	Continua > Physics 1 > Models > Adaptive Time-Step > Time-Step Providers > Volumetric Source
Requires	Time: Implicit Unsteady or PISO Unsteady Material: Multiphase. Multiphase Models: Volume of Fluid (VOF) or Mixture Multiphase (MMP). Optional Models: Fluid Film, Dispersed Multiphase (DMP), or Lagrangian Multiphase (LMP) A Phase Interactions model is required, or a user-specified volume fraction source.
Properties	Enable/Disable, Scaling Factor, Smoothing Steps,Cut-off Percentage. See Volumetric Source Properties.
Activates	Field Functions	Volumetric Source Proposal See Field Functions.

Volumetric Source Properties

Enable/Disable

See Adaptive Time-Step Provider Common Properties.

Scaling Factor

The ratio between the permissible phase transfer volume and the cell volume. This value is the scaling factor $C$ in Eqn. (107). The range for this property is 0.001 to 10, the default is 1 (phase mass transfer fills the cell volume per time-step).

Smoothing Steps

The number of smoothing steps. This value specifies the number of times that the volume-weighted smoothing operation (Eqn. (94)) is performed.

Cut-off Percentage

Specifies a percentage $p$ of small/bad cells to be ignored by the model. The prescribed cut-off percentage is used to find the quantile $t_{q} (p)$ such that for a given $p$ :

Figure 3. EQUATION_DISPLAY

\frac{# [c e l l s : Δ t_{c} \leq t_{q} (p)]}{# [a l l c e l l s]} \approx p %

(108)

The time-step is then set as $t_{q} (p)$ and any local time-steps that the provider proposes below this value will be ignored by the model. The range for this property is 0 (default) to 100.

Field Functions

The following field function is available when the Volumetric Source time-step provider is activated.

Volumetric Source Proposal: The Volumetric Source time-step proposal for each individual cell.