Hey,
When setting up a 3D porous media, you have to set up 2 unit vectors. These vectors represent the principal axes of the porous media.
There’s a rule though. The second unit vector must be normal to the first one. There’s actually a third unit vector which is automatically determined by the software (third vector being normal to the first 2).
For a simple example, it would look something like this (green block = porous media):
/Ric