# Diverging simulation

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 November 20, 2015, 05:01 #41 Member   Join Date: Sep 2015 Posts: 30 Rep Power: 11 Alright, so I will set my deltaT as 0.25E-4, maxCo as 0.5 and make the changes in the PIMPLE block, and see how it goes. Just wondering, would maxCo = 0.5 make my simulation to run for ages? Because initially I set it as 0.5 and its really crawling and I do not have that luxury of time.

 November 20, 2015, 05:57 #42 Senior Member     Matvey Kraposhin Join Date: Mar 2009 Location: Moscow, Russian Federation Posts: 355 Rep Power: 21 I saw this strange place in your fvSolution just now: Code: ```relaxationFactors { U 0.1; nuTilda 0.1; p 0.1; k 0.1; omega 0.1; }``` If you are doing transient simulation, you must set relaxation factors for all fields to 1. But, if you need only a steady-state solution, you can set relaxation factors as folows: Code: ```relaxationFactors { U 0.3; nuTilda 0.5; p 0.2; k 0.5; omega 0.5; }``` Then, you must set nOuterCorrectors to larger value, let's say about 10-50. And this will let you to increate deltaT to values with Co >> 1 Code: ```PIMPLE { nOuterCorrectors 20; nCorrectors 2; nNonOrthogonalCorrectors 0; pRefCell 0; pRefValue 0; }``` __________________ MDPI Fluids (Q2) special issue for OSS software: https://www.mdpi.com/journal/fluids/..._modelling_OSS GitHub: https://github.com/unicfdlab Linkedin: https://linkedin.com/in/matvey-kraposhin-413869163 RG: https://www.researchgate.net/profile/Matvey_Kraposhin

 November 20, 2015, 07:08 #43 Member   Join Date: Sep 2015 Posts: 30 Rep Power: 11 Yes, I'm running transient simulation. If I set all the relaxationFactors to 1, do I still need to set the nOuterCorrectors to 20 as well?

November 20, 2015, 07:15
#44
Senior Member

Matvey Kraposhin
Join Date: Mar 2009
Location: Moscow, Russian Federation
Posts: 355
Rep Power: 21
Quote:
 Originally Posted by czhongrong Yes, I'm running transient simulation. If I set all the relaxationFactors to 1, do I still need to set the nOuterCorrectors to 20 as well?
No, if you are running transient simulation, you don't need to use outer corrections, so you msut set nOuterCorrectors to 1. And all relaxation factors must be set to 1.

 November 20, 2015, 23:22 #45 Member   Join Date: Sep 2015 Posts: 30 Rep Power: 11 It seemed to be able to simulate past the error point. But its taking way too long~(about 6hours to reach 0.01) What are some ways where I can speed up the process without having it to diverge again?

 November 21, 2015, 07:17 #46 Senior Member     Matvey Kraposhin Join Date: Mar 2009 Location: Moscow, Russian Federation Posts: 355 Rep Power: 21 1) Increase maxCo to 0.8-0.9, but at the cost of chance of divergence 2) Use more CPU __________________ MDPI Fluids (Q2) special issue for OSS software: https://www.mdpi.com/journal/fluids/..._modelling_OSS GitHub: https://github.com/unicfdlab Linkedin: https://linkedin.com/in/matvey-kraposhin-413869163 RG: https://www.researchgate.net/profile/Matvey_Kraposhin