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Old   November 13, 2012, 02:37
Exclamation High Courant number
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Arun S
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I am performing LES of a roundjet using OpenFOAM. SGS model is smagorinsky.
Upto around 12500 time steps my courant number was well below 1 (0.5-0.7). After that it has been increasing and, now at 13750 iterations, it is ~14. Is the solution right? I am using a time step 5e-5. Why is this sudden increase in courant number happening?
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Old   November 13, 2012, 05:02
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Filippo Maria Denaro
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Originally Posted by arunsmec View Post
I am performing LES of a roundjet using OpenFOAM. SGS model is smagorinsky.
Upto around 12500 time steps my courant number was well below 1 (0.5-0.7). After that it has been increasing and, now at 13750 iterations, it is ~14. Is the solution right? I am using a time step 5e-5. Why is this sudden increase in courant number happening?
if your time-step is fixed then you have an increasing of the velocities, that can indicate a numerical instability
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Old   November 13, 2012, 11:38
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Arun S
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I am surprised why this instability has come up after these many timesteps
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Old   November 13, 2012, 12:10
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I am surprised why this instability has come up after these many timesteps
why not? numerical instability can be a slow process ...
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Old   March 28, 2013, 07:04
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Tushar Chourushi
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I am surprised why this instability has come up after these many timesteps
I agree with "FMDenaro",

@Arun...

The error usually builds up during iterations, try to add under-relaxation factor to the variables. Also, re-check your mesh.
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