# blockMesh problem

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December 4, 2009, 09:44
blockMesh problem
#1
Member

Dennis Rown
Join Date: Oct 2009
Posts: 51
Rep Power: 9
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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 December 8, 2009, 16:03 #2 Senior Member     Sebastian Gatzka Join Date: Mar 2009 Location: Frankfurt, Germany Posts: 729 Rep Power: 13 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? __________________ Schrödingers wife: "What did you do to the cat? It's half dead!"

 December 9, 2009, 06:00 #3 Member   Dennis Rown Join Date: Oct 2009 Posts: 51 Rep Power: 9 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.

December 9, 2009, 06:39
#4
Senior Member

Sebastian Gatzka
Join Date: Mar 2009
Location: Frankfurt, Germany
Posts: 729
Rep Power: 13
Quote:
 Originally Posted by shangzung 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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 December 9, 2009, 07:21 #5 Member   Dennis Rown Join Date: Oct 2009 Posts: 51 Rep Power: 9 But it does grow, since I use a gravity! It only disappears completely when the pipe steepness (mesh) exceeds certain gradient.

 December 9, 2009, 09:18 #6 Member   Dennis Rown Join Date: Oct 2009 Posts: 51 Rep Power: 9 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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