Seepage flow

The flow of one or more fluids ( phases ) through a porous medium , the migration of filter media, is referred to as seepage flow or seepage flow .

Such media are e.g. B. the soil , sand or the like, or the aquifer of the groundwater , but also other liquids (petroleum).

It is characteristic of a seepage flow that the flow behavior of the fluids involved is mainly determined by the pressure gradient and the conductivity of the medium. The effects of surface tension can optionally be taken into account as capillary pressure. The equations of seepage flows can be derived from the Navier-Stokes equations by simplifying assumptions . The Navier-Stokes equations model the transport and flow behavior of fluids, whereas the surface tension is only influenced at the edge of the area under consideration.

In theory, seepage flows could be described using Darcy's law . In general, however, the pore shape of the medium (e.g. the soil) is unknown. In addition, in the case of seepage flows, adsorption and storage effects in the pores ( capillaries ) of the medium are taken into account . In addition, a complete calculation of the flow behavior of the fluids in a complex structure of a porous medium would be very time-consuming. With seepage, however, the pore structure of the medium z. B. described by permeability and affinity constants ( permeability coefficient ). This enables an approximate description of the flow behavior.

Leakage flows can be described by partial differential equations . The best-known model for this is the Richards equation , which describes a seepage flow of an air-liquid mixture in a porous medium. By coupling several Richards equations, additional phases (i.e. fluids) can be added to the seepage flow model. So z. B. the spread of an oil-water mixture in the ground can be described.

One application of the seepage flow model is the modeling of groundwater, for example the spread of contamination in the ground with a groundwater model . In particular, by suitable choice of the boundary conditions of the descriptive partial differential equations, solutions for eliminating such contaminations can be determined.

A useful way of representing and calculating a seepage flow is the flow network .

See also

• Pore ​​water
• Capillary curvature pressure
• Leakage line (boundary between the leaked and non-leaked part of the porous medium)

literature

• Arthur Casagrande : Seepage through dams , Harvard University, Graduate School of Engineering in Cambridge, Mass., 1937