Problem with alpha.water > 1 in multiphase flow
 

Hello everyone!
I'm new to this community and I'm a beginner in openfoam programming so bare that in mind. I'm simulating a gas generation from a porous media into a liquid bassin. The two domains are resolved via two previously developed openfoam codes:
porous media code: Handles the generation of gas and the transport of gas governed by Darcy equation
liquid bassin code: Handles fluid flow (based on compressible flow)


I developed a code for the interface boundary conditions for:alpha.water, U and P


The U and P conditions are the based on pressurePermeableAlphaInletOutletVelocity and prghPermeableAlphaTotalPressureFvPatchScalarField that are used in the dam break tutorial.


For the alpha.water condition, I want to precise that when the gas pressure in the porous medium surpasses that of the neighbouring cell in the liquid bassin, the gas bubble can flow and thus:


if(p_Porous>p_Bassin):

{
this->refValue()=0.9;
this->valueFraction()=1,0;
}


else
{
this->refValue()=1.0;
this->valueFraction()=0,0;
}



However, the alpha.water during calculations becomes greater than 1 and, at some point, the simulation diverges because of a "negative initial temperature".


What is wrong with the conditions specified? what might be the source of the error?


Any help is appreciated.


Thanks




initial conditions for alpha.water:


boundaryField
{
walls
{
type zeroGradient;
}
atmosphere
{
type inletOutlet;
inletValue uniform 0;
value uniform 0;
}
interface
{
type coupledmixedAlphaMultiphaseBC; (developed library)
neighbourFieldName poreMedia;
value uniform 1;
}
}



For the U file:


boundaryField
{
walls
{
type fixedValue;
value uniform (0 0 0);}

atmosphere
{
type pressureInletOutletVelocity;
value uniform (0.0 0.0 0.0);
}

Interface
{
type coupledMixedVelocityMultiphaseBC ; (developed library)
value uniform (0 0 0);
alphaMin 0.01;

}





and for the P file:


boundaryField
{
walls
{
type fixedFluxPressure;
}
atmosphere
{
type totalPressure;
p0 uniform 101325;
U U;
phi phi;
rho rho;
psi none;
gamma 1;
value uniform 101325;
}


Interface
{
type mycoupledmixedPressureMultiphaseBC; (developed library)
value uniform 101325;
alphaMin 0.01;

}