libraries_porousBoundaryConditions_darcyGradPressure

darcyGradPressure BC

Description

This boundary condition provides a fixed gradient condition for pressure p, pressure head h or potential potential to impose fixed Darcy velocity. After computing the flux phi corresponding to the fixed velocity U, fixed gradient is computed as:

grad(p) = - (phi-phiG-phiPc)/M

where phi is the total flux, phiG the gravity-induced flux, phiPc capillary-induced flux and M the phase mobility (depends on the solver used)

Solver specificities

• all solvers except impesFoam: phiPc = 0

• saturated quasi-2D solvers (groundwater2DFoam, groundwaterTransport2DFoam, steadyGroundwater2DFoam) : phiG = 0

• Phase mobility expression:

  • Two-phase flow solver: M = K x kr / mu with K the permeability, kr the relative permeability and mu the dynamic viscosity.

    impesFoam

  • saturated quasi-2D solvers: K x g x rho / mu: with g the gravity and rho the density

    groundwater2DFoam, groundwaterTransport2DFoam, steadyGroundwater2DFoam

  • unsaturated groundwater solvers: K x g x rho x kr / mu

    groundwaterFoam, groundwaterTransportFoam, steadyGroundwaterFoam

Usage

<patchName>
{
    type            darcyGradPressure;
    phiName         phi; // optional (phi by default)
    value           uniform 0; // optional initial value (necessary for paraview display)
}

Comments

This boundary generally requires a fixedValue BC on velocity which may be variable in time and in space (darcyGradPressure updates pressure gradient at each time iteration).

Restrictions

This boundary works for most solvers except anisoImpesFoam which requires the use of darcyGradPressureAniso due to its tensorial permeability field.

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