Learning Forum

[cs437]

Hi,

 

Please see the attached file. The file is a non-conformal mesh; however, at the air-liquid interface the node is not aligned when meshing. For VOF with the figure, Vf water and air is initially 1 and 0, which seem to be correct.

I also did another mesh approach "a conformal mesh", which interface boundary disappeared at the boundary condition. The mesh looked nicer and nodes aligned properly at interface; however, when I do VOF, at the interface Vf water and air become some fraction between 0-1 meaning not only red and blue contour plot I saw on that plane. 

I would like to know which way it is more proper for air-liquid interface.

 

Best regards,

 

[cs437]

[Keyur Kanade]

If I understand your question correctly, you want to say that after VOF run, you will get very volume fraction of 0 and 1 only. 

At start of the simulation, you will get volume fraction as 0 or 1 in all cells. But when you run VOF, the cells at interface will have volume fraction between 0 to 1. Please see help document for more information on VOF and how equations are solved. 

 

[cs437]

Hi,

 

It is not like what you meant. I do as follows:

I have three domains: air domain on the top, liquid outer domain, and liquid inner domain.

I used adaption and patched the cell zone to have their volume fraction initially. 

The attached figure is when I do conformal mesh in my geometry including at two-fluid interface. As seen, we see some ratio of air-water at the interface when initialization. When I did that with non-conformal mesh, I used to see ONLY blue and red in the beginning. I know that when I do conformal mesh, the interface boundary zone could not be identified. Therefore, I would like to know which set-up is more appropriate if I do MRF and if I do sliding mesh.

[Rob]

Replot the above with node values off: you're picking up the graphics smoothing. You may also want to review the mesh resolution on the interface. 

Reference frame  & sliding mesh are both valid approaches, and both/either are commonly used in very similar applications.  Maybe show what you're modelling and we can tell you what to look out for.  A good starting point is the tutorials (via Help in Fluent) and User's Guide & Theory Guide to understand the approach used in the reference frame model. 

[cs437]

Hi,

I got it and I am looking for vortex formation. What do you mean by reviewing the mesh resolution on the interface since this is conformal mesh and there is no interface boundary condition. Did you mean real interface phenomena between two fluids? If that, I think I need to do more meshes at the real liquid-liquid interface by dividing a stationary domain into sub-volumes to mesh at specific location. 

 

Thank you.

[Rob]

You'll want to refine the mesh around the interface. I'd advise reading the manual regarding VOF and dynamic adaption rather than try and pre-mesh if you're looking at vortex formation.