Porous-media flow
= Porous-media flow
{wiki}
<Porous-media flow> is <fluid> motion through the interconnected voids of a <porous medium>, such as a sand bed, a rock or a filter. Individual passages can be tiny and tortuous, yet their combined discharge can be predicted without resolving every passage. <Darcy law> supplies this bulk description when viscous resistance dominates pore-scale inertia; <porosity> measures how much space stores <fluid>, while <permeability of a porous medium> measures how readily that space transmits it.
The basic fully saturated model assumes one <Newtonian fluid> fills the connected pore space of a stationary solid framework, with <incompressible flow>, a small pore-scale <Reynolds number>, and averaging volumes large compared with individual pores but small compared with macroscopic variations. These are assumptions of the model developed below, rather than a claim that <Darcy law> describes every <porous-media flow>. <Two-phase porous-media flow> and <poroelastic aquifers> require additional constitutive and storage information.
For a first calculation, see <Darcy flow through a homogeneous slab>: a pressure drop determines the discharge, but <porosity> determines the corresponding <pore velocity>. <Layered porous permeability> then shows how geometry alone can make the bulk response <anisotropic>.