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Old   December 4, 2009, 09:44
Default blockMesh problem
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Dennis Rown
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Hello!

I have a problem with blockMesh. I modelled a tube with a hole on an upper side where water (alpha1 = 1) flows in. The problem is, when I change the z-values of the mesh to a high number, the water disappears from the simulation. As in the example picture I attached it works for the z value "3" on the outer blocks. When I choose a higher z-value, water disappears. What can cause this?
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Old   December 8, 2009, 16:03
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Sebastian Gatzka
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What is your boundary condition for the inflow?
Did you set up a small value of water (liquid phase volume fraction) which you have fogotten with your simulations z>3?
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Old   December 9, 2009, 06:00
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My boundary conditions for alpha1, p and U are:

alpha1:

walls
{
type zeroGradient;
}
ends
{
type inletOutlet;
inletValue uniform 0;
value uniform 0;
}

inletHole
{
type inletOutlet;
inletValue uniform 1;
value uniform 1;
}

p:

walls
{
type buoyantPressure;
value uniform 0;
}

ends
{
type totalPressure;
p0 uniform 0;
U U;
phi phi;
rho rho;
psi none;
gamma 1;
value uniform 0;
}
inletHole
{
type totalPressure;
p0 uniform 0;
U U;
phi phi;
rho rho;
psi none;
gamma 1;
value uniform 0;
}

U:

walls
{
type fixedValue;
value uniform (0 0 0);
}
ends
{
type pressureInletOutletVelocity;
value uniform (0 0 0);
}
inletHole
{
type pressureInletOutletVelocity;
value uniform (0 0 0);
}

I am not sure if this conditions are correct, because i tried to take them from a 2D sample case into this 3D case.

What I found out is that when I switch boundary conditions of "walls" and "ends" it works (the water does not disappear, but falls through the walls)

Sorry, I do not understand, what you mean with that I forgot the value of water with the simulations of z>3.
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Old   December 9, 2009, 06:39
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Quote:
Originally Posted by shangzung View Post

I am not sure if this conditions are correct.
I'm not sure either, but I will give you my thoughts about them.
You are using a prediscribed boundary value for alpha and velocity at the inlet. But your velocity is set to zero (uniform (0 0 0)).
So how should water "grow" inside your domain?

If you specify an amount of water in the proximity of the inlet there maybe some results because the CSF-model can compute forces on the drop.
But with no inflow-velocity your amount of water will not grow.
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Old   December 9, 2009, 07:21
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But it does grow, since I use a gravity! It only disappears completely when the pipe steepness (mesh) exceeds certain gradient.
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Old   December 9, 2009, 09:18
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Looks like with your information (usinng a downward velocity at the inlet) it seems to work even with the steep mesh. Water does not disappear instantly!

Thanks a lot!
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