# Extrusion with FreeSurface

Dear all,

I am trying to simulate an extrusion process of a liquid (say high viscous fluid) into the ambient. I have a cylindrical nozzle in which there is my fluid. After the nozzle there is the ambient with air. The fluid is dragged towards the ambient by a pressure difference between inlet and ambient pressure. I would like to simulate the expansion of the fluid in the ambient using the TwoPhaseFields3D<T,DESCRIPTOR> fields, like in the showcase damBreak3D:

In main I call:
setToFunction(fields.flag, fields.flag.getBoundingBox().enlarge(-1), setFlags);

where setFlags is:
int setFlags(plint iX, plint iY, plint iZ)
{
plint cy=ny/2; //center of the nozzle y
plint cz=nz/2; //center of the nozzle z
T rSqr = util::sqr(iY-cy) + util::sqr(iZ-cz);
bool insideNozzle =
iX < nx/3 && //one third of the domain
rSqr <= radius*radius;

``````if(insideNozzle)
{
return twoPhaseFlag::fluid;
}
else if(iX>nx/3)
{
return twoPhaseFlag::empty;
}
else return twoPhaseFlag::wall;
``````

}

This works, but I have 2 problems:

1. The nozzle gets empty during the simulation, while I would like to have a running flow
2. The fluid now is dragged by an external force. I tried to impose a dirichlet B.C. on the nozzle inlet (an overpressure),
but the fluid is not dragged by this overpressure and do not expand outside the nozzle.

I would really appreciate if someone can give me some advice: 1) how can I have a running flow in the nozzle (i.e. nozzle always full)? How can I impose the B.C. in a two phase problem like this?

Thank you in advance.

Alex