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CFL condition: can a mass balance problem arise if violated?

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Old   August 21, 2011, 10:52
Default CFL condition: can a mass balance problem arise if violated?
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I'm a newbie to fluid dynamics. I'm trying to figure out the source of some strange results in code that I wrote for tracking concentrations during advection/diffusion.

If there is a problem with the time step I use (i.e., if the time step violates the CFL condition), could that lead to mass balance problems?
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Old   August 22, 2011, 11:37
Default your question is not easy to answer
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according to my experimence,

if you violate the CFL condition , you could not get the convergent solution

however, it is not easy to define accurately the CFL condition for most numerical methods

and even if you know the CFL condition, people would use a safety factor;

best wishes
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Old   August 23, 2011, 03:12
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Thanks a lot.
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Old   August 24, 2011, 15:12
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Quote:
Originally Posted by bzz77 View Post
I'm a newbie to fluid dynamics. I'm trying to figure out the source of some strange results in code that I wrote for tracking concentrations during advection/diffusion.

If there is a problem with the time step I use (i.e., if the time step violates the CFL condition), could that lead to mass balance problems?

Hm, typically, if you violate the CFL condition by a considerable amount, your code blows up.... it might however be that you are dancing around the permittable CFL number, and your code is somewhat semi-stable....that might indeed lead to an mass balance problem....however, that's just a theory....

try the following: take half of your CFL an rerun your code. if the problem persists, you can rule out the time step. What kind of scheme are you using? FV?

Post back here if you need any more help!

Cheers!
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