0 (i.e. Boundary Conditions)

The BC works on the Patches which have been defined in the mesh and the guessing of the first value of the field pass through the voice

internal field

which can be filled with a uniform, but it could be changed in non-uniform if set values in system/setFieldsDict and then apply this change through setFields

Commmon types of boundary conditions:

The most common types of patches are:

fixedValue

Every face associated to the boundary is set to the conditions

zeroGradient

Matematically speaking it is a symmetry conditon hence it implements at the boundaries: \[ ∂ϕ ∕ ∂x = 0 \]

Where “x” is the space and ϕ is a field properties.

symmetryPlane

Applied to planar patches to represent a symmetry condition, equivalent to zeroGradient.

symmetryPatch
{
    type            symmetryPlane;
    ...
}

noSlip

It is a velocity condtion and it is equivalent to:

wallPatch
{
    type            fixedValue;
    value           0;
}

empty

To set a 2D simulation

frontAndBack
{
    type        empty;
}

AMIcyclic

Impose a periodic BC when the patches in study have not the same mesh, it must be declared the nature of periodicity (rotational, translation). The separationVector must contain the distances between the 2 patches in study. It is advised to use a createPatchDict to modify the BC after snappy procedure of snappyHexMesh because can cause problems to the patches)

calculated

Calculate the value from its component in the field, this doesn’t work for transport quantities but only for variable define by a formulae (for instance nut)

totalPressure

which is a fixedValue condition calculated from p and U field

pressureInletOutletVelocity

Which applies a zeroGradient on all components, except where there is inflow, in this case a fixedValue condition is applied to the tangential component

inletOutlet

It is a zeroGradient condition when outwards, fixedValue when flow is inwards

  {
    type inletOutlet;
    inletValue uniform (0 0 0); // value of the velocity
    value uniform x;            // value of the properties
  }

Basically, inletOutlet is zero gradient unless the flow is inward in which case it is fixed value (inletValue). outletInlet is zero gradient if the flow is inward and fixed value (outletValue) if the flow is outward.