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Daniel January 18, 2008 03:57

about Courant number
During calculation, my Courant number was larger than 1, then, is my outcome correct?

what does Courant number really mean? Is it only for watching the stability?

What if some of my time step's largest courant number is larger than 1 (or 5 or what)? In what limitation can I believe my solution is good?

Many thanks,


Usman January 19, 2008 22:23

Re: about Courant number
Courant number is stability as well as accuracy requirement. I order to have accurate solution you should keep it close to unity. Large courant number may improve the stability of simulation but it will be at the cost of accuracy.


Deepak January 20, 2008 12:24

Re: about Courant number
I also believe that is also deals with convergence, as when my solution starts diverging, lowering your Courant no is a good option..

Please correct me if i am wrong. Thanks, Deepak

pankaj February 2, 2008 14:47

Re: about Courant number
hi, Courant number is responsible for stability of explicit scheme. If, you use implicit scheme then you dont have to think for courant no. But, if it is explicit , then, if it cross 1, your code will, always use less courant no. usually 1/4......

Daniel February 9, 2008 02:58

Re: about Courant number
Hi there,

thank you all.

If my discretization schemes of temporal and convective and viscous terms are implicit, but my pressure terms are explicit. (you know, I am trying to use OpneFOAM).


1. do I need to think for courant no.?

2. what do you mean by saying " use less courant no. usually 1/4", are there any references that I can rely on?

3. Again I want to know, whether my result is "correct" once my courant number was larger than one during calculation?

4. What's the relationship between "stable" and "correct"? I mean what if my courant no. is, say 2 or 3, of which you say it is unstable, can i believe my result to be correct? Must I be concerned for stability all the way?

Thanks for your patience.

And finally, Happy new year to you all. (I 'm from China)


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