Porous Regions Workflow

To simulate a porous material, set the region type to Porous Region, then set the porosity and the inertial and viscous coefficients. These are required for the porous source term in the momentum equation. If a turbulence model is active, specify turbulence quantities downstream of the porous region. An option is also available to control the use of porous media flux.

1. Select the node Regions > [porous region].
2. Set Type to Porous Region.
3. Under the selected region, select Physics Values > Porosity and set the value of the Method property. Do likewise for Physics Values > Tortuosity.

   Porosity $\chi$ and tortuosity $\tau$ are used to scale the diffusion coefficients for species and passive scalar transport. Porosity is used to calculate the effective thermal conductivity in the porous region.

   Porosity is defined as the ratio of open volume to total volume of the porous region, and is entered as a scalar profile. For unsteady flow calculations, the porosity is used to modify the fluid density $\rho$ in the time derivative terms of the continuity, energy, and species equations; $\rho$ is replaced by the product $\rho \chi$. This substitution reflects the fact that the fluid occupies only part of the volume. For effective thermal conductivity, the porosity is used to blend the thermal conductivities of the fluid and solid materials that are represented within the porous region. See Superficial Velocity Formulation.

   Tortuosity is defined as the ratio between actual (convoluted) path length between two points in the porous material and the length of the straight path connecting the same points. The higher the tortuosity of a porous region, the lower the rate of diffusion, since the convoluted paths slow down the spread of the diffusing material.

4. Specify porous resistance. The porous inertial resistance ${\mathbf{\text{P}}}_i$ and the porous viscous resistance ${\mathbf{\text{P}}}_v$ are defined as tensor profiles. You specify these properties for the region.
   • Select [porous region] > Physics Values > Porous Inertial Resistance and select the value of the Method property. Repeat for Porous Viscous Resistance.

   • For multi-phase flows, for each phase, select [porous region] > Phase Conditions > [phase] > Physics Values > Porous Inertial Resistance. Select the value of the Method property and specify the local orientation and the values of each component of the selected tensor.

     Repeat for Porous Viscous Resistance.

     In the [porous region] > Physics Values > Porous Inertial Resistance and Porous Viscous Resistance, the Method property is automatically set to Mixture Porous Inertial Resistance and Mixture Porous Viscous Resistance, respectively.

5. If you are using the Segregated Flow model, decide whether to solve for momentum fluxes. By default, the momentum equation is solved with the addition of terms for convection and viscous fluxes. See Eqn. (1843). To omit these terms, edit the Regions > [porous region] > Physics Conditions > Porous Media Flux Option node, then activate the Discount Momentum Fluxes property.

   Omitting these terms reduces computational expense, but the flow solver becomes less robust. Therefore, it is best to use the default setting.

6. If you are using the VOF Multiphase model or Eulerian Multiphase Mixture model, decide whether to add user-specified volume fraction sources.

   To add these sources, select the Regions > [porous region] > Physics Conditions > Volume Fraction Source Option node, then activate the Phase Source Term property.

   Under the Physics Values node, specify the Volume Fraction Sources, Volume Fraction Sources Pressure Derivative, and Volume Fraction Sources Volume Fraction Derivative.

7. If the flow through the porous region is turbulent, select the Turbulence Specification node in the Physics Conditions manager. This node contains a Method property that provides several options for how turbulence scales are set within the porous region. Specify the appropriate turbulent quantities under the Physics Values node.

   The turbulence transport equations are not solved for in the porous regions. Turbulence quantities in the fluid leaving the porous region are constructed from the user-defined values; they are not transported from the upstream side of the porous region.

8. If the simulation involves energy transport across porous regions, specify the thermal properties of the porous solid material and of the fluid passing through it. When one of the fluid energy models is active, the following values are provided in the Physics Values node of a porous region:
   • Solid Density
   • Solid Specific Heat
   • Solid Thermal Conductivity

   The fluid energy models are Coupled Energy, and the Segregated Fluid Enthalpy, Temperature, and Enthalpy models.