I am seeking to model a simple bubble growth/collapse in Ansys. I have tried using 2D, VOF with an initial patch air circle geometry surrounded by water. I include surface tension and make the air have ideal gas density. I also patch the air space to have pressure difference (have tried both higher and lower pressure than static water pressure). After calculating, the water-air interphase does not grow or collapse, it only "wiggles"/has small oscillations. Am I missing some setting that is important? Any feedback is helpful, thank you.
Hi,
I guess, that you try this in a closed domain (all side faces are walls)?
If yes, than this could be the issue. If Water is specified as incompressible media, than a shrinking of the bubble should cause an expansion of the Water phase (occupation of a larger volume). But if Water is incompressible and if your domain has no openings, than this is a contradictory assumption and the bubble cannot shrink or expand.
The situation should change, if you make e.g. the upper boundary condition an opening and allow water to flow into your domain. Thereby the inflow of Water could compensate for the amount of volume which is made available by the shrinking air bubble due to air compressibility.
Please correct me, if my assumption (about the closed domain) was wrong for your setup.
Regards,
Dr. Th. Frank.
you can specify an inlet at the boundary and provide an inlet velocity or flow rate for the secondary phase and the bubble size and shape produced are calculated with surface tension between the phases unless you want to model the bubbles individually and let them float. The diameter indicated for secondary phase in Mixture and Eulerian methods is to provide a mean diameter to take into account for the drag force between the phases. (i.e. air bubble spheres moving through the continues phase). And if the application needs to include drag/lift forces apart from surface tension, the VOF on its own doesn't give that option. So, in that case an Eulerian coupled with MF VOF can be a appropriate model. However, the calculation will take much longer than VOF due to more complex equations.
Hi,
Considering a free surface for water in your domain with a deforming mesh in the contact region between the water and air may help.
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