 # Porous Media

A Porous medium can be defined to specify porousity characteristics of the computational domain.

To model a porous mediuam, navigate to Advanced Concepts and under Porous Media add a new porous medium. The following models are supported:

## Darcy-Forchheimer

This porousity model takes non-linear effects into account by adding inertial terms to the pressure-flux equation. The model requires both Darcy d and Forchheimer f coefficients to be supplied by the user. The model leads to the following source term:
$$\vec{S} = – (\mu d + \frac{\rho |\vec{U}|}{2} f) \vec{U}$$
where μ represents dynamic viscosity, ρ density, and $$\vec{U}$$ velocity.

The Darcy d coefficient is the reciprocal of the permeability κ.
$$d = \frac{1}{\kappa}$$
If the coefficient f is set to zero, the equation degenerates into the Darcy equation.

## Fixed coefficients

This model requires α and β to be supplied by the user. The corresponding source term is:
$$\vec{S} = – \rho_{ref} (\alpha + \beta |\vec{U}|) \vec{U}$$

Additionally, a coordinate system specifies the main directions of the porous zone resistance. The vectors $$\vec{e_1}$$ and $$\vec{e_3}$$ are unit vectors. The vector $$\vec{e_2}$$ is implicitly defined such that $$(\vec{e_1} \vec{e_2} \vec{e_3})$$ is a right-handed coordinate system like (xyz). The x, y and z components for d and f correspond to the vectors $$\vec{e_1}$$, $$\vec{e_2}$$ and $$\vec{e_3}$$ respectively. It can be used to define non-isotropic porosity. For isotropic media, all 3 values should be identical.

Once the setup is complete, a porous region must be assinged. Such a region can be defined using Geometry Primitives.