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Time-dependent simulation stuck at 4% progress

Posted 2023年6月16日 GMT-4 11:44 Chemical, General, Computational Fluid Dynamics (CFD) Version 6.1 1 Reply

ssh80
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Hello,

I'm using the turbulent flow and dilute chemical transport modules to model a concentration gradient through a reaction chamber. My time dependent simulation does not progress past 4% without even starting the first timestep. This lasts for an hour before it quits on its own.

I've attached my .mph file below. Any help/suggestions are appreciated

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1 Reply Last Post 2023年6月19日 GMT-4 06:11
Igor Rusu
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Posted: 10 months ago 2023年6月19日 GMT-4 06:11
Updated: 10 months ago 2023年6月19日 GMT-4 06:13

At first glance I can see that your physics are not coupled. You have no inlet/outlet BC for the transport of diluted species physics, nor are your transport properties coupled to the flow. Maybe you decided to only solve one physics but that is not apparent from the model you posted.

Secondly, you have a wide range of geometrical sizes which leads to high resolution mesh requirements. This is the warning I obtain upon meshing your geometry: Number of vertex elements: 38
Number of edge elements: 3111
Number of boundary elements: 83436
Number of elements: 1612463
Minimum element quality: 0.004827
Warning: Low minimum element quality
Do you think this might have something to do with your solution time?
Thirdly, you are not ramping up your boundary condition, as is advised in virtually any COMSOL Blogpost/documentation. Another option would be to solve the turbulent flow first, then use that as the initial solution for you concentration study.
Lastly, I advise experimenting with a simpler geometry, one physics at a time rather than delve into the actual problem immediately.
For reference: https://www.comsol.com/blogs/viscosity-ramping-improves-the-convergence-of-cfd-models/
https://www.comsol.com/blogs/improving-convergence-multiphysics-problems/
https://www.comsol.com/blogs/how-to-place-inlet-and-outlet-boundary-conditions-in-cfd-simulations/
Kind regards,
Igor

At first glance I can see that your physics are not coupled. You have no inlet/outlet BC for the transport of diluted species physics, nor are your transport properties coupled to the flow. Maybe you decided to only solve one physics but that is not apparent from the model you posted. Secondly, you have a wide range of geometrical sizes which leads to high resolution mesh requirements. This is the warning I obtain upon meshing your geometry: Number of vertex elements: 38 Number of edge elements: 3111 Number of boundary elements: 83436 Number of elements: 1612463 Minimum element quality: 0.004827 **Warning: Low minimum element quality** Do you think this might have something to do with your solution time? Thirdly, you are not ramping up your boundary condition, as is advised in virtually any COMSOL Blogpost/documentation. Another option would be to solve the turbulent flow first, then use that as the initial solution for you concentration study. Lastly, I advise experimenting with a simpler geometry, one physics at a time rather than delve into the actual problem immediately. For reference: https://www.comsol.com/blogs/viscosity-ramping-improves-the-convergence-of-cfd-models/ https://www.comsol.com/blogs/improving-convergence-multiphysics-problems/ https://www.comsol.com/blogs/how-to-place-inlet-and-outlet-boundary-conditions-in-cfd-simulations/ Kind regards, Igor

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