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

How to estimate numerical diffusion ?

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

LinkBack Thread Tools Display Modes
Old   June 2, 2001, 01:55
Default How to estimate numerical diffusion ?
Posts: n/a
We come across the term 'numerical diffusion' (ref. contributions by S.V. Patankar and B.P. Leonard). We perhaps experience it (problem specific) especially when using lower order upwind scheme for the convection term. Is there any way to estimate the quantity of 'numerical diffusion' - localised or in the domain?
  Reply With Quote

Old   June 2, 2001, 09:22
Default Re: How to estimate numerical diffusion ?
Jim Park
Posts: n/a
This analysis technique is detailed by C. W. Hirt, "Heuristic Stability Theory for Finite-Difference Equations," J. Comp. Physics, v. 8, p. 119 (1968).
  Reply With Quote

Old   June 6, 2001, 02:26
Default Re: How to estimate numerical diffusion ?
Praveen C
Posts: n/a
One way is to consider inviscid subsonic flow in which there should be no entropy production. Whatever entropy is generated is purely due to numerical dissipation.
  Reply With Quote

Old   June 19, 2001, 09:35
Default Re: How to estimate numerical diffusion ?
Mike Noskov
Posts: n/a
In the textbook on Numerical Methods (such as Tannehill et al 1997) you can find the expression for the numerical diffusion due to the upwind first order discretization of the convective (first derivative) terms. It has the form: u*h/2

u-velocity, h-grid spacing

To see how large is your artificial diffusion, send a vortex in the still fluid. Integrate the vorticity over the domain for each time step. There is an analytical experssion for the decay of vorticity. See how the numerical integration correspond to analytical function.
  Reply With Quote


Thread Tools
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 On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Moving mesh Niklas Wikstrom (Wikstrom) OpenFOAM Running, Solving & CFD 122 June 15, 2014 06:20
Numerical Diffusion in CFX John S. CFX 4 August 17, 2008 19:47
Numerical diffusion. jinwon Main CFD Forum 2 June 27, 2007 11:42
Estimation of numerical diffusion varghese FLUENT 0 March 24, 2003 06:02
How to Estimate Numerical Diffusion Jon Johnson Main CFD Forum 3 November 4, 1999 15:00

All times are GMT -4. The time now is 23:32.