CFD Online Logo CFD Online URL
Home > Forums > General Forums > Main CFD Forum

RMS Courant Number vs MAX Courant Number

Register Blogs Members List Search Today's Posts Mark Forums Read

LinkBack Thread Tools Search this Thread Display Modes
Old   June 15, 2010, 01:32
Default RMS Courant Number vs MAX Courant Number
New Member
Join Date: Aug 2009
Posts: 7
Rep Power: 16
zoozoozoo is on a distinguished road
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.
zoozoozoo is offline   Reply With Quote

Old   August 19, 2010, 09:38
New Member
Freddie Sizer
Join Date: Apr 2009
Posts: 19
Rep Power: 17
f_sizer is on a distinguished road
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.
f_sizer is offline   Reply With Quote

Old   June 11, 2012, 01:24
Default Hi
Senior Member
Join Date: Nov 2011
Posts: 179
Rep Power: 14
Danial Q is on a distinguished road
IN my transient simulation of homogeneous multiphase problem involving free surface also, i have RMS courant Number = 0 , Max Courant nUmber = 0 , is it OK??? If not what could be the problem??

Danial Q is offline   Reply With Quote

Old   June 12, 2012, 13:44
Senior Member
Ford Prefect's Avatar
Join Date: Mar 2009
Posts: 151
Rep Power: 17
Ford Prefect is on a distinguished road
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.
"Trying is the first step to failure." - Homer Simpson
Ford Prefect is offline   Reply With Quote


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
[mesh manipulation] Mesh Refinement Luiz Eduardo Bittencourt Sampaio (Sampaio) OpenFOAM Meshing & Mesh Conversion 42 January 8, 2017 12:55
DecomposePar unequal number of shared faces maka OpenFOAM Pre-Processing 6 August 12, 2010 09:01
On the damBreak4phaseFine cases paean OpenFOAM Running, Solving & CFD 0 November 14, 2008 21:14
IcoFoam parallel woes msrinath80 OpenFOAM Running, Solving & CFD 9 July 22, 2007 02:58
Could anybody help me see this error and give help liugx212 OpenFOAM Running, Solving & CFD 3 January 4, 2006 18:07

All times are GMT -4. The time now is 12:36.