Macro Porosity Model Reference

The Macro Porosity model is used to detect shrinkage-related defects in a solidifying liquid with temperature-dependent density. The Macro Porosity (fully coupled) model is used in a full VOF simulation to model flow, pressure, and thermal effects. The Macro Porosity (pure thermal) model is used with a pure thermal simulation to model only the solidification process of the melt.

Table 1. Macro Porosity Model Reference
Model Names	Macro Porosity (fully coupled)
	Macro Porosity (pure thermal)
Theory	See Macro Porosity Formulation. Applies to the Macro Porosity (fully coupled) model only.
Provided By	[physics continuum] > Models > Multiphase Interaction > Phase Interactions > [phase interaction] > Models > Optional Models
Example Node Path	[physics continuum] > Models > Multiphase Interaction > Phase Interactions > [phase interaction] > Models > Macro Porosity (fully coupled)
Requires	A VOF Multiphase simulation with the following models selected: Space: Axisymmetric, Two Dimensional, or Three Dimensional Time: Implicit Unsteady Material: Eulerian Multiphase Eulerian Multiphase Model: Volume of Fluid (VOF) Energy: Segregated Fluid Isothermal or Segregated Multiphase Temperature Optional Models: Pure Thermal (required for the Macro Porosity (pure thermal) model only) A minimum of two VOF phases: a liquid phase (for the melt) and a gas phase (for the pores/void). The liquid phase must be a single-component liquid and have a temperature-dependent density, such as User Defined EOS or Polynomial Density. The gas phase must be a single-component gas. For the Macro Porosity (fully coupled) model only, the gas must be compressible. A phase interaction with the following setup: The VOF-VOF Phase Interaction model activated, with the Primary Phase set to the liquid phase and the Secondary Phase set to the gas phase. Phase Interaction Topology: VOF-VOF Phase Interaction Optional Models: Macro Porosity (fully coupled) or Macro Porosity (pure thermal)
Properties	See Macro Porosity (pure thermal) Model Properties and Macro Porosity (fully coupled) Model Properties.
Activates	Model Controls (child nodes)	For the Macro Porosity (pure thermal) model: Solid Cell Indicator Pore Probability Indicator See Macro Porosity (pure thermal) Child Nodes.
	Field Functions	See Field Functions.

Macro Porosity (pure thermal) Model Properties

The Macro Porosity (pure thermal) model has the following property:

Verbose: When activated, writes an output before the first iteration of each time-step. This output details the amount of the primary phase (melt) that is replaced by the secondary phase (void).

Macro Porosity (fully coupled) Model Properties

The Macro Porosity (fully coupled) model has the following properties:

Void Pressure: The pressure $p_{void}$ in Eqn. (354) below which a gaseous phase void is assumed to outgas from the liquid phase. The default value is 50000 Pa.
Under-Relaxation Factor: At each iteration, this property governs the extent to which the newly computed void phase fraction supplants the old solution. The default value is 1.0.
Scaling Factor: The scaling factor in the Macro Porosity (fully coupled) model is a multiplicative factor to the source rate of the void phase. This value is $s$ in Eqn. (360). Limited to $s \geq 0$ .
See Variation of the Scaling Factor.

Macro Porosity (pure thermal) Child Nodes

The Macro Porosity (pure thermal) model has the following child nodes:

Solid Cell Indicator

Identifies the cells that are considered solid and the cells that are fluid. Macro porosity can occur only for liquid zones that are fully enclosed by either wall boundaries or solid cells. A value of zero indicates a fluid cell, a non-zero value indicates a solid cell. A Liquid Zone Index value is assigned to each liquid cell, indicating the enclosed liquid zone to which the cell belongs. Shrinkage, and consequently the target amount of melt that is replaced by void to keep the melt mass constant, is computed for each of the cell clumps that have the same Liquid Zone Index.

If you choose the Field Function method, the Flow Stop Flag field function is set automatically. This is a built-in field function that is available with the Melting-Solidification model. See Melting-Solidification Model Field Functions.

The default setting is a constant value of 0.

Pore Probability Indicator

Identifies the cells within which melt is replaced with void in cases of shrinkage, in order of priority. For each group of cells that have the same Liquid Zone Index, the replacement of the target amount of melt with void is performed first in the cell that has the maximum value for the pore probability.

For expansion, the inverse value of the pore probability is used to determine the cells in which the void phase is replaced with liquid phase.

For example, when the Gravity Potential method (the default setting) is used for the pore probability profile:

To model shrinkage, the liquid phase is replaced in the upper-most cells of the liquid zone that contain liquid phase.
To model expansion, the void phase is replaced with liquid phase in the lowest cells of the liquid zone that contain void phase.
If no void phase is available in the liquid zone, the mass change of the liquid zone cannot be compensated for. A mass conservation error can result.

Method	Description
Gravity Potential	The phase replacement takes place in the highest (with respect to the gravity vector) cells of each enclosed liquid region. After the phase replacement, the melt volume is the same as it was at the beginning of the previous time-step. If no gravity model is selected for the simulation, it is considered a zero-gravity simulation and the pore probability is uniformly zero.
Pressure Field	The phase replacement takes place in the cells of each enclosed liquid region where the absolute pressure is minimal. After the phase replacement, the melt volume is the same as it was at the beginning of the previous time-step.

Field Functions

The following primitive field functions are available to the simulation when the Macro Porosity (pure thermal) model is used.

Contiguous Stopped Region Index: A domain-wide unique index of contiguous stopped regions. This is used to indicate that a cell belongs to a certain liquid zone enclosed by either flow-stopped cells or boundaries.
Liquid Zone Index of <phase interaction>: Index of the contiguous liquid zone. A Liquid Zone Index value is assigned to each liquid cell, indicating the enclosed liquid zone to which the cell belongs. Shrinkage, and the appropriate phase replacement, is computed for each of the zones that have the same Liquid Zone Index.
Phase Replacement Volume Fraction Limit of <phase interaction>: Positive values indicate shrinkage, negative values indicate expansion.