Learning Forum

[sivaraman-s]

Hi all, 

I have a technical doubt in ANSYS intrepretation of phases in VOF multiphase. I am using VOF model for modelling multiphase boiling using Lee model. In my phases, I have one as pure liquid and other as a mixture of vapor and air. I have enabled species transfer model.

My problem is, since FLUENT solved the volume fraction equation only for secondary phases, I wanted to have the mixture as my secondary phase instead of pure liquid. However, my simulation diverges when I use mixture as my secondary as opposed to using liquid as my secondary phase. Can you tell me is this a limitation in FLUENT or in your opinion there is any error ? 

PS: I created my mixture using 'mixture template', constant density for air (air was taken from FLUENT database) and ideal gas EOS for vapor material.

Thanks in advance

[SRP]

Hi,

In general, you can specify the primary and secondary phases whichever way you prefer. It is a good idea, especially in more complicated problems, to consider how your choice will affect the ease of problem setup.

Also refer to this forum discussion: https://forum.ansys.com/forums/topic/secondary-mixture-phase-in-vof-model/

To understand more please refer theory guide: https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v222/en/flu_th/flu_th_sec_multiphase_vof.html

If you are not able to access the link, please refer to this forum discussion: Using Help with links (ansys.com)

Thank you

Saurabh

[sivaraman-s]

Thanks. I will check

Also, when I enable species transfer, by creating mixture materials. Does it apply only for one of the phases (if I have 3 phases) or species transfer will apply to all phases chosen in the model?

Thank you 

[SRP]

Hi,

The material chosen for the mixture will be subject to species transfer.

Thank you

Saurabh

[sivaraman-s]

Hi, 

Just adding another question of doubt in the context of the thread. 

I have tried two different simulations, 1. Case with mixture of vapor/air as my primary phase (species transport) and secondary as liquid.

2. Case with liquid as my primary phase and mixture as my secondary phase. 

In case 1, everything seems physical. Primarily, I would expect mass transfer rate to be zero after initialization before starting the simulation and this is correct in case 1. However, in case 2, where liquid is my primary phase, after initialization, my mass transfer rate is always a "non-zero value". There is unstable solution and possible divergence which I believe could be attributed to this issue. 

Can anyone kindly explain why fluent intreprets this way?  

Thanks in advance

PS: I use FLUENT 2020 R2