Specifying Bidirectional and Orthotropic Porous Media

When the porous medium is not isotropic, Discovery offers the option to specify viscous and inertial resistance coefficients in the streamwise and crossflow directions.

To specify the direction, you must first select Porous from the Fluid Flow dropdown menu in the Simulation tab ribbon. Select one or more fluid bodies and set the Directionality option to Bidirectional or Orthotropic. Use the Direction tool guide to set the primary direction by selecting a face, edge, or axis. The following table summarizes how directionality is defined based on different filter shapes:

Directionality Example Description
Linear

Any selection of a straight edge, plane, planar face will define the streamwise direction​.

The selected surface does not need to be on the porous media body.​

*Some shapes can be assumed linear bi-directional or could be idealized as such.​
Cylindrical and conical

Selecting either the inner or outer cylindrical surface, or a circular edge, will define it with a cylindrical coordinate system, with streamwise being normal to the selected face. Cones are also supported if a face is selected (angle detected from face).​

The surface selection does not have to be on the media. Therefore, if you have an irregular shape (typically rotationally symmetric) with which you want a cylindrical cross-section to be used, choose another axially aligned cylinder or circular line (such as an inlet pipe).
Composite For ovals or other shaped filters, use multiple filter bodies, and a combination of cylindrical and linear bi-directional definitions.​
The following images explain the different directions of the viscous and inertial resistance coefficients using the selected geometry (highlighted in orange) as a reference to set the primary direction.