[Daveed]

Hi guys. I want to change boundary condition type within the solver. how can I do it. for example initially Pressure boundary condition on a patch is fixedFluxPressure and I want when I reach certain time during simulation, change it to fixed value with specified value. (I want to do this from solver)

boundaryField
{
Left
{
type fixedFluxPressure;
}

.
.// other BCs
.

}


then change it to :

boundaryField
{
Left
{
type fixedValue;
value 1e5;
}

.
.// other BCs
.

}

[Daveed]

finally i found it and i leave this reply to my post maybe help another one with this issue some days later.

to change boundary condition type for a field, first you must find patch id of that face.

label leftFacePatchID = mesh.boundaryMesh().findPatchID("Left");
const polyPatch& leftPatch = mesh.boundaryMesh()[leftFacePatchID];

then you can set boundary type with this syntax: (for example if pressure is desired field with p notation)

p.boundaryFieldRef().set(leftFacePatchID , fvPatchField<scalar>::New("fixedValue", mesh.boundary()[leftFacePatchID ],p));

in above, first argument of New() must be boundary type, and for example here it sets BC to fixedValue.
then to assign a value to this fixed value BC, we must go through all cells face in patch and set desired value.

forAll(leftPatch , faceI)
{
p.boundaryFieldRef()[leftFacePatchID][faceI] = pressureValue;
}