T-Junction buyoancy driven flow.

Multiphase Mikal · April 27, 2016, 05:44

Hi all,

I'm currently trying to simulate a multiphase T-Junction where the inlet is pumping air into a fluid filled channel.

Like this:

..........................| outlet. |
..........................| to bulk |
..........................| liquid...|
..........................|.......... |
..........................|.......... |
_______________|.......... |
Velocity gas................... |
Inlet .............................. |
--------------------------- ..........|
...........................|......... |
...........................|......... |
...........................| .........|
...........................|.. Inlet |
...........................| from.. |
...........................|.. Bulk |
...........................| Liquid |

I've set up my case by modifying the damBreak tutorial case in interFoam, and according to checkMesh, my mesh is "OK", plus, using paraFoam, my velocity inlet seems to be fine and my alpha.water phase fraction seem to be fine.

However, when i go to run my case with adjustable time step, my courant number peaks and my deltaT drops (as a result) to around 1.e-7 kind of values, which seem unreasonable.

What can I do to solve this, or has anyone done this type of simulation before or do they have some template code that I can use??

Just really confused as to why my case isn't running properly.

akidess · April 27, 2016, 11:54

Such a value is reasonable for microfluidic devices:
http://www.cfd-online.com/Forums/ope...tml#post574191

Multiphase Mikal · April 28, 2016, 15:09

Quote:

Originally Posted by akidess

Such a value is reasonable for microfluidic devices:
http://www.cfd-online.com/Forums/ope...tml#post574191

Hmmmm, I looked around and it does seem reasonable according to other people simulating microfluidic flow domains.

My problem is, the speed is far too slow for me (it would take several months to simulate 1 second) at that timestep; is there anything I can do to speed it up?

Perhaps change the solver or something?

Incidentally, I changed the dimensions of my mesh and ran the simulation, it ran in a reasonable amount of time with a timestep of around 0.005 seconds and seemed reasonable, so really it seems to be the mesh size that is my problem.

Will coarsening my mesh have much effect? Or is my best bet to just change the solver?

akidess · April 29, 2016, 01:53

Part of your study will have to include a mesh refinement test to determine the influence on your results.

April 27, 2016, 05:44	T-Junction buyoancy driven flow.	#1
Multiphase Mikal New Member Michael Olsen Join Date: Apr 2016 Posts: 2 Rep Power: 0	Hi all, I'm currently trying to simulate a multiphase T-Junction where the inlet is pumping air into a fluid filled channel. Like this: ..........................\| outlet. \| ..........................\| to bulk \| ..........................\| liquid...\| ..........................\|.......... \| ..........................\|.......... \| _______________\|.......... \| Velocity gas................... \| Inlet .............................. \| --------------------------- ..........\| ...........................\|......... \| ...........................\|......... \| ...........................\| .........\| ...........................\|.. Inlet \| ...........................\| from.. \| ...........................\|.. Bulk \| ...........................\| Liquid \| I've set up my case by modifying the damBreak tutorial case in interFoam, and according to checkMesh, my mesh is "OK", plus, using paraFoam, my velocity inlet seems to be fine and my alpha.water phase fraction seem to be fine. However, when i go to run my case with adjustable time step, my courant number peaks and my deltaT drops (as a result) to around 1.e-7 kind of values, which seem unreasonable. What can I do to solve this, or has anyone done this type of simulation before or do they have some template code that I can use?? Just really confused as to why my case isn't running properly.

April 27, 2016, 11:54		#2
akidess Senior Member Anton Kidess Join Date: May 2009 Location: Germany Posts: 1,377 Rep Power: 29	Such a value is reasonable for microfluidic devices: http://www.cfd-online.com/Forums/ope...tml#post574191 __________________ On twitter @akidTwit Spend as much time formulating your questions as you expect people to spend on their answer.

April 29, 2016, 01:53		#4
akidess Senior Member Anton Kidess Join Date: May 2009 Location: Germany Posts: 1,377 Rep Power: 29	Part of your study will have to include a mesh refinement test to determine the influence on your results. __________________ On twitter @akidTwit Spend as much time formulating your questions as you expect people to spend on their answer.

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