G'day,
I want to use Coupled scheme to calculate this case and therefore need to setup a suitable CFL number (Courant number). The CFL number in this scheme isn't used to calculate adptive time step size, a relaxation factor instead. As the pic shows its reciprocal is used as a relaxation factor, and the user's guide suggests that
If ANSYS Fluent immediately diverges in the AMG solver, then the CFL number is too high and should be reduced. Reducing the CFL number below 10 is not recommended since......In most transient cases, the CFL number should be set to a large value such as 10^7 and explicit relaxation factors to 1.0.
Well, 10≤ CFL ≤10^7 is such a wide range, so what value is good to start with?
Hope someone can help me. Thanks so much!
Hi Milne Ando
Your definition of CFL number is incorrect. Please refer any CFD fundamental book. Moreover, use CFL number less than 0.1. Then your simulation will work.
thanks
Deepak Kumar Pandey hi,
well I know the definition of CFL number which is used to calculate adaptive time step size. However, the CFL number I'm discussing is Flow Courant number which is totally different from original CFL number. It seems only ANSYS used this specific term as an under-relaxation factor. And the user's guide gives a wide range of Flow Courant number; I didn't find any paper discussing how this term can affect the accuracy of results. But I found someone give a relatively clear answer:
https://www.cfd-online.com/Forums/fluent/226708-fluent-courant-number-value.html
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