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 solver: phiPc = 0
saturated quasi-2D solvers (groundwater2DFoam solver, groundwaterTransport2DFoam solver) : 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.
saturated quasi-2D solvers: K x g x rho / mu: with g the gravity and rho the density
unsaturated groundwater solvers: K x g x rho x kr / mu
Usage
<patchName>
{
type darcyGradPressure;
phiName phi; // optional (phi by default)
value uniform 0; // optional initial value (necessary for paraview display)
}
Restrictions
This boundary works for most solvers except anisoImpesFoam solver which requires the use of darcyGradPressureAniso BC due to its tensorial permeability field.
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).