# Porous media

Homogeneous porous media are modeled by the addition of a momentum source term, \(\boldsymbol{S}_{pm}\), to the fluid momentum equation.

\[\boldsymbol{S}_{pm} =-\frac{\mu_f}{C_1} \boldsymbol{u}_f - C_2\frac{1}{2}\rho_f\lvert \boldsymbol{u}_f \rvert \boldsymbol{u}_f\]

\(\mu_f\), \(\rho_f\), and \(\boldsymbol{u}_f\) are the fluid viscosity, density, and velocity and \(C_1\) and \(C_2\) are user defined constants.

The following inputs are defined using the `pm` prefix.

| Description | Type | Default
--- | --- | --- | ---
regions | Regions used to define porous media. | String | None
[region].volfrac | Solids volume fraction of the porous media region. | Real | None
[region].c1 | Porous media permeabilty constant for the source term in fluid momentum equation. | Real | None
[region].c2 | Porous media inertial resistance factor for the source term in fluid momentum equation. | Real | None
[region].allow_particles | Allow particles to flow through the porous media region. | Int | 0