[sarrazs]

Hello
does the control volume of the space averaging in the Navier-Stokes equations in CFX defined as the control volume for the numerical discretization? In other terms do the control volume of the space averaging depends on the mesh size.

[ghorrocks]

Yes and yes.

The CFX documentation (theory manual) describes in detail how the control volumes are constructed from the mesh.

[sarrazs]

Originally Posted by ghorrocks

Yes and yes.

The CFX documentation (theory manual) describes in detail how the control volumes are constructed from the mesh.

Thank you for your reply. In the CFX documentation, they describe the control volumes for the numerical discretization.
In my case, I'm simulating bubble column with the Euler-Euler approach with mean diameter 4mm. For very fine mesh when the control volume contains only air how cfx resolve the problem and how does he calculate the interfacial forces. And I think this is more absurd for the Euler-Lagrange model when the control volume is inside a bubble.

[ghorrocks]

In euler-euler models and euler-lagrange models the interphase effects are simply applied at the control volume level. There is no concept of phases becoming large enough that a full control volume would now be one phase or another.

For instance the drag of the bubble creates a force, and that force is applied to the control volume. But the size of the initial bubble is not used to work out whether the individual bubble affect one or multiple control volumes. It is simply the volume fraction field which is used to do this.

So if you are looking for the effects of individual bubbles you need to consider higher resolution modelling approaches like free surface models.