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zoozoozoo June 15, 2010 01:32

RMS Courant Number vs MAX Courant Number
Hi all,

sorry for confronting you guys with such a stale topic.

I thought when everybody is talking about the Courant Number, such as CFL has to be less than 1 etc. ...
it is addressed to the max Courant number.
Now I've read the following sentence in Ansys CFX, 12.1 Help:
"For accuracy, the average Courant (or CFL) number should be in the range of 0.5-1. "
What does it mean? Do I have to consider the RMS Courant number.

Help will be appraciated

Thanks in advance.

f_sizer August 19, 2010 09:38

This is related also to mesh size.

Since the courant number is calculated using dx (distance between cell centre or interface depending on solver) what this means is that in regions where the flow is fast you need smaller cells to achieve the courant number value of between 0.5 and 1.

Danial Q June 11, 2012 01:24

IN my transient simulation of homogeneous multiphase problem involving free surface also, i have RMS courant Number = 0 , Max Courant nUmber = 0 :eek:, is it OK??? If not what could be the problem??


Ford Prefect June 12, 2012 13:44

Accuracy and stability. If you use an explicit scheme and violate the CFL condition then stability should suffer. However the Courant number should be as close to unity as possible for accuracy. When it comes to accuracy then I guess that you could use an average value for the entire mesh.

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