max courant/courant...velocity spikes?

mdjames · September 1, 2010, 12:55

Hi all,

I'm running a turbulent half-channel flow (dynSmag). I'm wondering why the max courant number is being reported in the neighborhood of 10-12 while the mean courant is around 0.3, where i calculated it based on expected mean flow.

Where might these wild velocity fluctuations be coming from?

Thanks very much for any help!

alberto · September 17, 2010, 00:59

Have you very refined cells somewhere in your domain?

mdjames · September 17, 2010, 13:08

Ah, yes. I have some near wall refinement but only in the wall normal direction. Eddy generation and therefore v and w velocities occurring I suppose?

stevenvanharen · September 21, 2010, 15:06

Have the same "problem" in my channel flow LES/DNS.

If you are interested you can use the Co utility to determine where the high Courant number appears.

maysmech · September 24, 2010, 03:32

Hello,
i have two questions.

Quote:

Originally Posted by mdjames

Hi all,

I'm running a turbulent half-channel flow (dynSmag). I'm wondering why the max courant number is being reported in the neighborhood of 10-12 while the mean courant is around 0.3, where i calculated it based on expected mean flow.

How can you find mean courant number? because in terminal min and max courant number is displaying only.

Quote:

Originally Posted by stevenvanharen

Have the same "problem" in my channel flow LES/DNS.

If you are interested you can use the Co utility to determine where the high Courant number appears.

Is it possible to tell more about Co utility?

stevenvanharen · September 24, 2010, 04:20

Which solver are u using? I get mean and max Co in my terminal window using channelFoam/channelOodles.

Co utility should be in your openfoam folder. Just use Co -help to see how it works.

maysmech · September 24, 2010, 05:44

Quote:

Originally Posted by stevenvanharen

Which solver are u using? I get mean and max Co in my terminal window using channelFoam/channelOodles.

Co utility should be in your openfoam folder. Just use Co -help to see how it works.

i use pisoFoam. i want solve a rearward facing step with RAS and LES. my problem is i don't know how much can courant be large in solving process. do you know about it?

stevenvanharen · September 24, 2010, 06:26

RAS, no idea
LES, max CFL ~ 0.5

maysmech · September 24, 2010, 09:13

Quote:

Originally Posted by stevenvanharen

RAS, no idea
LES, max CFL ~ 0.5

Thanks for your reply.
is it a law for LES or it depends on cases? also please tell your reference.
Best regards.

September 1, 2010, 12:55	max courant/courant...velocity spikes?	#1
mdjames New Member Matt James Join Date: Jun 2010 Location: Marinette,WI, USA Posts: 25 Rep Power: 15	Hi all, I'm running a turbulent half-channel flow (dynSmag). I'm wondering why the max courant number is being reported in the neighborhood of 10-12 while the mean courant is around 0.3, where i calculated it based on expected mean flow. Where might these wild velocity fluctuations be coming from? Thanks very much for any help!

September 17, 2010, 00:59		#2
alberto Senior Member Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,912 Rep Power: 36	Have you very refined cells somewhere in your domain? __________________ Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats (current status: http://albertopassalacqua.com/?p=1541) OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using.

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September 17, 2010, 13:08		#3
mdjames New Member Matt James Join Date: Jun 2010 Location: Marinette,WI, USA Posts: 25 Rep Power: 15	Ah, yes. I have some near wall refinement but only in the wall normal direction. Eddy generation and therefore v and w velocities occurring I suppose?

September 21, 2010, 15:06		#4
stevenvanharen Senior Member Steven van Haren Join Date: Aug 2010 Location: The Netherlands Posts: 149 Rep Power: 15	Have the same "problem" in my channel flow LES/DNS. If you are interested you can use the Co utility to determine where the high Courant number appears.

September 24, 2010, 04:20		#6
stevenvanharen Senior Member Steven van Haren Join Date: Aug 2010 Location: The Netherlands Posts: 149 Rep Power: 15	Which solver are u using? I get mean and max Co in my terminal window using channelFoam/channelOodles. Co utility should be in your openfoam folder. Just use Co -help to see how it works.

September 24, 2010, 06:26		#8
stevenvanharen Senior Member Steven van Haren Join Date: Aug 2010 Location: The Netherlands Posts: 149 Rep Power: 15	RAS, no idea LES, max CFL ~ 0.5