Beginner's question: VoF vs two-phase

[ed mumei]

Hi,

I have read several examples and test cases, but I am not sure I understand correctly the main differences between VOF and two-phase. In particular, the page for two-phase.h mentions "The interface between the fluids is tracked with a Volume-Of-Fluid method". Could someone please explain to me how the two methods differ, and when should one use one or the other?

Thank you!

Ed

[Amin Taziny]

Hi Ed,

I believe you have a misunderstanding: VoF and two-phase are not different methodologies. Two-phase flows are a class of fluid problems that are comprised of two-phases just as the name implies. When solving these fluid problems, different numerical implementations can be applied to account for the interface between each phase and how it evolves through the simulation. Volume-of-fluid is one of these methods to account for said interface and is the one described in the two-phase.h page.  

Hope this helps!

Amin

[ed mumei]

Thank you Amin for your reply.

I agree that in general VOF is just one of several possible methods to handle two-phase flows.

It seems that, in Basilisk, two-phase.h implies vof.h but one can also use vof.h without two-phase.h. However, all the examples using vof.h (without two-phase.h) are indeed two-phase flows, aren't they?

• Axisymmetric mass conservation
• Capillary wave
• Shape oscillation of an inviscid droplet
• Time-reversed VOF advection in a vortex
• Sessile drop

etc.

So, when should one use vof.h or two-phase.h?

Thank you,

Ed

[Karl Cardin]

Hi Ed,

I believe vof.h provides a method to advect volume fraction fields and two-phase.h provides a method to associate properties such as density and viscosity with the volume fraction field.

In examples where vof.h is used without two-phase.h the variation of properties is either not necessary or it is handled in some way independent from two-phase.h.

Best,

Karl