# Gravity influence

Taking into account the gravity in the darcyFoarm solver, is complex and needs a good basics in programming on OpenFoam.

Indeed having a gravity field involves a new boundary condition in the bottom of the domain on the pressure gradient.
Then the condition zero velocity on the bottom is expressed by :

then we have the following boundary condition on the pressure gradient:

After adding the gravity to the solver, we decided to compare the case with gravity to the case without gravity term that intervenes in Darcy law.
In this study the solver used is a solver without anisotropy, moreover the permeability will be equal to $K=7.10 {-7} \ m^2$.

Therefore we studied the influence of the gravity on the pressure and on the velocity fields :

# Gravity influence on the velocity field

Velocity field without gravity presence :

Velocity field with gravity presence :

We notice that the gravity has few impact on the velocity field.

# Gravity influence on the pressure field

Pressure without gravity field :

Pressure with gravity field :

We notice that the gravity decreases the negative maximum pressure.