[marsa27]

Originally Posted by ghorrocks

The opening is just a normal pressure opening. No special treatment at all. But in the port leading to the opening you apply a volume bulk momentum source to stop the glass phase only.

Excuse me, but I can't find the option to introduce the volume bulk momentum source in the patch where I set the opening condition. Where is it?
Then I don't understand that value put to stop the glass phase only.

Kindly can you explain in detail the steps and an example?

[ghorrocks]

You can't put it on the opening. You obviously don't understand what I am saying so I have posted this picture of what I mean. Does this explain it to you?


Vent.png

It shows a small vent port in the side of the cavity with a normal opening at the end. A bulk momentum source term at the start of the vent stops the glass phase from going down the port.

[marsa27]

Originally Posted by ghorrocks

You can't put it on the opening. You obviously don't understand what I am saying so I have posted this picture of what I mean. Does this explain it to you?


Attachment 74585

It shows a small vent port in the side of the cavity with a normal opening at the end. A bulk momentum source term at the start of the vent stops the glass phase from going down the port.

Pratically you propose to put some small ducts where the air can escape and internal to these ducts set a porous subdomain with a resistance that stop the glass and let to go out for the air. Is correct?

[ghorrocks]

Yes, but I propose more than just some resistance. Use a source term to totally stop the glass phase. Then the air can flow through it unimpeded, but the glass will be stopped from entering. This appears to be what you are looking for.

[marsa27]

Originally Posted by ghorrocks

Yes, but I propose more than just some resistance. Use a source term to totally stop the glass phase. Then the air can flow through it unimpeded, but the glass will be stopped from entering. This appears to be what you are looking for.

Ok Thank you. I have set a subdomain to activate a momentum source. Then what should I activate? A loss model or a general momentum source? And what value? How can these options to stop only the glass and also the air?
I attached a figure with the possible options to activate. Can you suggest me the better option? thank you.

[ghorrocks]

Use a general momentum source, with the source term set up to make the velocity of the glass phase zero. You can do this by using the old trick of a source term to set the velocity to a defined value. This link describes how to do it: how to set velocity in certain place in CFX5

(And it also describes how long I have been around here )

[marsa27]

Thank you. But I cannot understand how this source is valid only for the glass and not also for the air. There is not a specification on the fluid (VOF) in which to apply this source. So I fear that it stops all the fluids (both glass, both air)

[ghorrocks]

Have a look in the CFX documentation on bulk source terms and how it appears it can act on one phase only. See if that does what you want.

[marsa27]

Originally Posted by ghorrocks

Have a look in the CFX documentation on bulk source terms and how it appears it can act on one phase only. See if that does what you want.

Thank you. You are actually right the CFX documentations tells: "Bulk sources take account of the volume fraction of each phase when applying the source term" however it doesn't specify if that holds true both for VOF homogeneous, both for Inhomogeneous models. Then I reading some posts of this forum I have seen that a general momentum source can specify the velocity in a certain place of the domain. As regards I am interested to set the velocity of the glass to zero, while the air can escapes.
Now in the menu of the subdomain (that I attach here) CFX requires to set the X,Y,X component in [kg/(m^2*s^2)]: what value must I set to have a velocity of the glass zero? Then momentum source coefficient? Is then necessary specify for the momentum source coefficient an expression to make this coeffcient high only for glass.Vof>0?
Thank you

[ghorrocks]

Looking into the bulk option you are right, it does not appear to allow you to apply the source term to one phase only. You appear to be able to do it for mass fractions (so it works for multicomponent mixtures), but it does not work for volume fractions (so it does not work for multiphase models).

You might be able to do it in CCL rather than through the GUI. I have not tried that, I will leave it up to you to explore that.

I don't understand why you can do it for mass fractions but not volume fractions. But it suggests that what you are proposing (a vent which works for one phase only in a homogenous multiphase model) cannot be done.

In that case you may be restricted to making the holes small, so the high viscosity of glass and surface tension stops the glass phase going out the vent. Of course this is how the vents work in actual glass moulding - it is usually preferable to model what happens in the actual case anyway.