Simulation two Phase flow without Interfaction

sasanghomi · August 14, 2019, 04:00

Dear friends,

I am trying to simulate a piece of solid which is cooled down by two fluids (air and water) separately. In fact, there is no interaction between water and air. My question is that how I can simulate such case without going through two-phase modeling. Honestly, I don't want to deal with volume fraction and the like in order to simulate the case because the above mentioned fluids have no interactions and they just touch the solid separately.
The problem is that when I use one fluid in Pre-CFX, I cannot define two materials for the domains and I have to define two fluids (two phase) in order to specify two separate materials for my case.
Do you have any idea? Modeling a two-phase flow is the only solution that I can go through?

Best Regards

ghorrocks · August 14, 2019, 06:32

Modelling it as a two phase flow is the only approach which is officially supported. But there is an unsupported feature where you set the expert parameter "allow unmatched domain physics = True" (or a name very similar to that, do a search to get the exact wording) and then you will be able to set different fluids in different domains but not use a multiphase model. But be aware it is unsupported, so be careful.

sasanghomi · August 14, 2019, 07:49

Thank you so much.

Do you have any suggestions for the simplest setup for running a two phase simulation in which there is no interactions between two fluids (Air & Water)?
There are different models for multi-phase flow simulations. Any idea with the least computational cost?

ghorrocks · August 14, 2019, 08:21

If you want to run this as a multiphase model then set both fluids as continuous fluids just like for a free surface simulation. The only difference being you don't define any interface model or surface tension. Make sure the momentum equation, turbulence equation and heat (if you have it) are set to homogeneous. Then you are only adding a volume fraction equation so the additional cost is small.

But the biggest problem with this approach is that the large density difference between air and water is like to make convergence harder than a normal single phase model. You won't know if this is problem for you until you run it and try it.

sasanghomi · August 14, 2019, 12:48

So helpful, thank you for sharing your ideas.

August 14, 2019, 04:00	Simulation two Phase flow without Interfaction	#1
sasanghomi Senior Member Sasan Ghomi Join Date: Sep 2012 Location: Denmark Posts: 292 Rep Power: 15	Dear friends, I am trying to simulate a piece of solid which is cooled down by two fluids (air and water) separately. In fact, there is no interaction between water and air. My question is that how I can simulate such case without going through two-phase modeling. Honestly, I don't want to deal with volume fraction and the like in order to simulate the case because the above mentioned fluids have no interactions and they just touch the solid separately. The problem is that when I use one fluid in Pre-CFX, I cannot define two materials for the domains and I have to define two fluids (two phase) in order to specify two separate materials for my case. Do you have any idea? Modeling a two-phase flow is the only solution that I can go through? Best Regards

August 14, 2019, 06:32		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	Modelling it as a two phase flow is the only approach which is officially supported. But there is an unsupported feature where you set the expert parameter "allow unmatched domain physics = True" (or a name very similar to that, do a search to get the exact wording) and then you will be able to set different fluids in different domains but not use a multiphase model. But be aware it is unsupported, so be careful. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

August 14, 2019, 08:21		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	If you want to run this as a multiphase model then set both fluids as continuous fluids just like for a free surface simulation. The only difference being you don't define any interface model or surface tension. Make sure the momentum equation, turbulence equation and heat (if you have it) are set to homogeneous. Then you are only adding a volume fraction equation so the additional cost is small. But the biggest problem with this approach is that the large density difference between air and water is like to make convergence harder than a normal single phase model. You won't know if this is problem for you until you run it and try it. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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August 14, 2019, 07:49		#3
sasanghomi Senior Member Sasan Ghomi Join Date: Sep 2012 Location: Denmark Posts: 292 Rep Power: 15	Thank you so much. Do you have any suggestions for the simplest setup for running a two phase simulation in which there is no interactions between two fluids (Air & Water)? There are different models for multi-phase flow simulations. Any idea with the least computational cost?

August 14, 2019, 12:48		#5
sasanghomi Senior Member Sasan Ghomi Join Date: Sep 2012 Location: Denmark Posts: 292 Rep Power: 15	So helpful, thank you for sharing your ideas.