CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > General Forums > Main CFD Forum

COURANT NUMBER

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 26, 2006, 03:23
Default Re: COURANT NUMBER
  #21
diaw (Des Aubery)
Guest
 
Posts: n/a
Refer to "computational Fluid Mechanics & HeatTransfer", 2 ed., Tannehill J.C., Anderson D.A. & Pletcher R.H., Taylor & Francis.

Specifically refer to pages 88 & 89.

abs(c*dt/dx)<=1

where: c*dt/dx = Courant number.

Hopefully this reference should convince you of the reasoning behind the Courant Number. There will also be many others.

diaw...
  Reply With Quote

Old   February 26, 2006, 06:29
Default Re: COURANT NUMBER
  #22
AnotherCFDUser
Guest
 
Posts: n/a
Thanks for the reference DIAW (some sanity at last).

You do have to be careful using that definition with my previous examples though as you require the additional conditions c > 0 or c < 0 (I used a instead of c in my example) depending on whether the scheme is a FTBS or FTFS discretization (I'm sure you know this, I'm sure its in the text you reference but the comment may be useful for those who are just starting out). If the Courant number can;t be negative then concepts like upwinding and the Courant, Friedrichs, Levy condition would have no or very limited usefulness.

A little aside for our fiend A:

On the subject of negative non-dimensional numbers:

Pressure coefficient Lift Coefficient Pitching moment coefficient

are all examples of non-dimensional numbers that can have negative values without breaking the laws of Physics - and there are many, many, many more.

I believe you may be confusing the concept of non-dimensional numbers and similarity parameters. As I have said previously the Courant number is *not* a similarity parameter.

This will be my last word on the subject as there is very little left to say - the maths doesn't lie.
  Reply With Quote

Old   February 26, 2006, 12:16
Default Re: COURANT NUMBER
  #23
Hemal Shah
Guest
 
Posts: n/a
Courant number can be negetive if one can buy a negetive apple to quench ones negetive hunger.

compressible NS equations along with energy and continuity in cylindrical coordinates in conservative form, where to get those?

  Reply With Quote

Old   February 26, 2006, 19:10
Default Re: COURANT NUMBER
  #24
A
Guest
 
Posts: n/a
All what you have mentioned are, in your own words, Coefficients, in simple language, a group of definitins agreed upon by professionals of the science. NonDimensional variables on the other hand, arise as a result of nondimensionalising an equation describing a phenomenun, be it a physical, human science, biological, etc... Do you get the difference? You can do the same as Diaw, get a reference book, read and understand it ..... Good Luck
  Reply With Quote

Reply

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
Courant number fireman FLUENT 7 September 11, 2021 12:33
IcoFoam unstability, courant number gets large! vivien OpenFOAM 11 March 9, 2017 04:45
LES near wall model & courant number kasim CFX 5 March 16, 2008 19:23
IcoFoam parallel woes msrinath80 OpenFOAM Running, Solving & CFD 9 July 22, 2007 03:58
Courant number calculation - unsteady flow Kuba FLUENT 0 November 8, 2005 23:44


All times are GMT -4. The time now is 16:58.