Learning Forum

[drocha]

I am modeling a stratified air and water flow inside a pipe using VOF with adaptive meshing in Fluent. The air velocity is about 40 times higher than the water velocity.
In the initial moments, velocities much higher than the air velocity appear at the air/water interface, leading to the formation of artificial waves near the domain inlet. These waves dissipate over time, and the results become consistent, but it consumes unnecessary processing time.
What could be the possible causes of this phenomenon and how can it be avoided?

[jcooper]

Hi:

Since the artefacts you are describing coincide with the air/water interface (where the mesh adaption also acts), I suspect that the mesh adaption is causing the high velocities. I have seen similar things happen in my own calculations.

I would consider making a mesh that already has refinement where it will be needed throughout the calculation.  You will gain back the time that is lost while the solution recovers from the adaptions, and there will be less chance of losing (or creating) momentum/energy/mass as the solution is transferred during the refinement process.

Best Regards,

Judy