[japanese student]

Hello!
I'm so happy if you give me some advice.

I want to use multi fluid vof model to study single bubble behavior.

Questions
1.Can I use the model to study it?
2.What is the Diameter in the secondary phase dialog box?
Is it the bubble diameter I want to study?

Thank you!

[LuckyTran]

Originally Posted by japanese student

Hello!
I'm so happy if you give me some advice.

I want to use multi fluid vof model to study single bubble behavior.

Questions
1.Can I use the model to study it?
2.What is the Diameter in the secondary phase dialog box?
Is it the bubble diameter I want to study?

Thank you!

1. Probably. The multifluid vof model is highly appropriate for bubbly flows in a liquid (dispersed bubbles in a flowing fluid). Is this what you have?
2. It's better described as an average particle size of the dispersed phase and typically the Sauter mean diameter is used. But it's basically going to become your bubble diameter. See section 17.5.5 in Fluent Manual for more details.

http://en.wikipedia.org/wiki/Sauter_mean_diameter

[japanese student]

Thank you very much for your reply!

I study single bubble(diameter=3mm) behavior using VOF(1 fluid model).
So, I don't focus on bubbly flow.

I focus on the mass transfer from the gas to the liquid.
But I can't study the momentum transfer between the gas and the liquid using VOF(1 fluid model) (section 17.7.1).
I want to study it by two fluid model, because I can study the momentum transfer.

Question.
1.If I can study single bubble behavior using multi fluid vof, is the diameter 3mm in the dialog box (fig.1)?

Thank you!

[famon]

Hello, I think VOF is not appropriate for bubbly flow, VOF is availabe when your phases have distinct layer, for example Slug.
for Bubbuly (velocity of 1st and 2nd phases are different according to their density) so Eulerian might be good choice as I know
This is what I know :-)

Originally Posted by japanese student

Thank you very much for your reply!

I study single bubble(diameter=3mm) behavior using VOF(1 fluid model).
So, I don't focus on bubbly flow.

I focus on the mass transfer from the gas to the liquid.
But I can't study the momentum transfer between the gas and the liquid using VOF(1 fluid model) (section 17.7.1).
I want to study it by two fluid model, because I can study the momentum transfer.

Question.
1.If I can study single bubble behavior using multi fluid vof, is the diameter 3mm in the dialog box (fig.1)?

Thank you!

[LuckyTran]

Originally Posted by famon

Hello, I think VOF is not appropriate for bubbly flow, VOF is availabe when your phases have distinct layer, for example Slug.
for Bubbuly (velocity of 1st and 2nd phases are different according to their density) so Eulerian might be good choice as I know
This is what I know :-)

Multi fluid VOF is an Eulerian model. Multi Fluid VOF is different than Volume of Fluid model.

[japanese student]

I understand the difference between VOF and multi fluid VOF.

I'll do my best for my reseach.

Thank you for your reply!

[japanese student]

If anyone has some ideas for my reseach, please tell me.

My reseach: mass transfer from the gas(single bubble) phase to the liquid phase.

Thank you!

[masoud.ravan]

Hi everyone,
I have a question about the Multi-Fluid VOF Model that would be accessible when the Eulerian Model is enabled in Ansys Fluent. According to Ansys Fluent help (17.5.19) “The multi-fluid VOF model provides a framework to couple the VOF and Eulerian multiphase models”. As others mentioned (Cerne et al.,2001; Strubelj and I. Tiselj, 2011; and some other published papers), in order to develop a coupled model, It’s necessary to choose a model to deal with both sharp and dispersed interface regimes and also deploy an appropriate switching criteria to recognize and distinguish these two interfaces and switch the solving approach. For example, one can choose the Mixture or Two-Fluid model for the dispersed interface regime and VOF or Level Set for the sharp interface regimes. I would be appreciated if anyone could give me more details about theory, equilibriums and switching criteria of Multi-Fluid VOF model.
Thanks in Advance

[Rohtiwari]

Hi everyone,

In the Fluent manual, there is no detailed theory about Eulerian multi-fluid VOF model. As per my knowledge it includes interface tracking model in Eulerian model. My question is regarding coupling behaviour. How is it coupled with momentum equation? Can anyone give a good reference for coupling of interface modeling?

Thanks in advance.

[masoud.ravan]

Originally Posted by Rohtiwari

Hi everyone,

In the Fluent manual, there is no detailed theory about Eulerian multi-fluid VOF model. As per my knowledge it includes interface tracking model in Eulerian model. My question is regarding coupling behaviour. How is it coupled with momentum equation? Can anyone give a good reference for coupling of interface modeling?

Thanks in advance.

What do you mean by "coupling of interface modeling?"?
briefly, this model could capture sharp interface between phases by using a special discretization scheme called the Compressive Advection Scheme. If you want more on this issue, see these two papers:

"Zwart, Philip J., Alan D. Burns, and Paul F. Galpin. "Coupled algebraic multigrid for free surface flow simulations." Proc. OMAE2007, San Diego, California, USA, June (2007): 10-15."

"Vallée, Christophe, et al. "Experimental investigation and CFD simulation of horizontal stratified two-phase flow phenomena." Nuclear Engineering and Design 238.3 (2008): 637-646."

[Rohtiwari]

Thanks for your reply. Actually, I am using sharp/dispersed interface modelling and I want to know how does Fluent decides the type of interface between sharp and dispersed? What is the criteria for switching from stratified region to dispersed region?

[masoud.ravan]

Originally Posted by Rohtiwari

Thanks for your reply. Actually, I am using sharp/dispersed interface modelling and I want to know how does Fluent decides the type of interface between sharp and dispersed? What is the criteria for switching from stratified region to dispersed region?

When you have enabled sharp/dispersed modelling, an interface modelling option would be available, in that option, you could check phase localized or zone localized.
For instance, by enabling phase localized you could define the value of compressive coefficient between each phases which indicates the degree of sharpening of an interface between selected phases.