Momentum transport mechanism for water flow over porous media

The momentum transport phenomena at the interface of the porous medium and fluid have been numerically investigated. The single domain approach is used with matching boundary conditions; that is, the Brinkman-Forchheimer-extended Darcy equation is used for the present study. Five typical porous media found in natural and engineered systems are selected in order to cover a wide range of the Darcy number (6.25 × 10^-4 ≤ Da ≤ 5.90 × 10^-11). In addition, six different Reynolds numbers (10 ≤ R ≤ 1,000) are tested for each case. When Da > 10^-7, the results showed the importance of viscous shear in the channel fluid. The viscous shear propagates across the interface into the porous medium and forms a transition region of disturbed flow in the porous medium. The depth of penetration is only dependent on the Darcy number of the porous medium rather than the Reynolds number and the shape of velocity profile. In the vicinity of the interface, it is clear that Darcy's law is inappropriate to describe flow in a permeable wall fracture or flow over porous media.