The momentum balance equation relating a pressure gradient \nabla p in porous medium with the induced fluid flow (percolation) with velocity {\bf u}:
(1) | {\bf u} = - \frac{k}{\mu} \ \nabla p |
where
Only valid for relatively slow percolation: { \rm Re} < 2,000
For a wider range of flow regimes see Forchheimer Equation.
See also
Physics / Fluid Dynamics / Percolation