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-   -   droplet simulation (http://www.cfd-online.com/Forums/openfoam/67491-droplet-simulation.html)

andre_001 August 17, 2009 04:07

droplet simulation
 
Hi
I am new to open FOAM (using it since last Monday). I try to simulate a droplet which forms itself out of a pipet. I use the InterFoam solver and just changed the geometry from the dambreak tutorial. My geometry looks like two cylinders on top of each other (the lower one is the bigger one, filled with air at the beginning of the simulation and the upper cylinder is a small cylinder filled with water at the beginning of the simulation). For all the walls of the lower (big) cylinder (except the wall that is in connection with the upper cylinder) I use the bc:
Pressure (0/pd):
{
type totalPressure;
U U;
phi phi;
rho none;
psi none;
gamma 1;
p0 uniform 0;
value uniform 0;
}
Velocity (0/U):
{
type pressureInletOutletVelocity;
phi phi;
value uniform (0 0 0);
}
For the wall where the water comes in (the upper surface of the upper cylinder) I use the bc:
pressure:
{
type totalPressure;
U U;
phi phi;
rho none;
psi none;
gamma 1;
p0 uniform 5000;
value uniform 0;
}
Velocity:
{
type pressureInletVelocity;
phi phi;
rho rho;
value uniform (0 0 0);
}
For the Mesh I used wedges. The initialization of gamma (volume fraction of water/air) is similar to the dambreak tutorial.
My problem is that there is not really a formation of a droplet but instead I just see a jet. When I use the same boundary conditions with a mesh that is not a wedge but a two dimensional mesh (actually three dimensional but with only one node in the z-direction) composed of two rectangels (instead of the two wedge-pieces representing the cylinders) I see a lot of disturbances in the jet and also some flow separation going on (indicating to me that this is a rather physical solution (may be not the best one but on the right track)).
My question now is: Is there a problem with the capability of a wedge-mesh to correctly calculate surface tension effects in the middle (at the axis of the wedge) of the cylinder?
Thanks for any comment on this.


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