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

Residue of FD scheme doesn't fall to machine zero?

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   May 4, 2004, 12:31
Default Residue of FD scheme doesn't fall to machine zero?
  #1
Practitioner
Guest
 
Posts: n/a
Dear all, I wish to enquire something about FD schemes.

I am solving an incompressible viscous steady state flow using a finite difference, fractional step method on the Navier Stokes equations on a non-staggered grid. I use the SOR method to solve for the Pressure Poisson equation.

I realise that my momentum residues and mass residue (using the momentum and continuity equations) do not fall to machine zero. Instead, most often the residues will only drop to magnitudes of around order 10^-3 to 10^-5. Is this because that finite difference schemes are essentially non-conservative in nature?

Thank you!
  Reply With Quote

Old   May 5, 2004, 01:38
Default Re: Residue of FD scheme doesn't fall to machine z
  #2
Praveen
Guest
 
Posts: n/a
A common cause for failure of convergence is the use of non-differentiable limiters like min-max. Are you using some sort of limiter ? Also look at the L<sub>&infin;</sub> residue and find where the maximum change is taking place. That might shed some light on your problem.
  Reply With Quote

Old   May 12, 2004, 03:56
Default Re: Residue of FD scheme doesn't fall to machine z
  #3
Practitioner
Guest
 
Posts: n/a
Hi,

I don't believe I'm using any limiters, and the residues don't really show anything significant. So it is possible for residues to fall to machine zero using finite difference? Or does the use of a non-staggered, collocated grid cause the "non-conservativeness"?
  Reply With Quote

Old   May 12, 2004, 05:46
Default Re: Residue of FD scheme doesn't fall to machine z
  #4
Praveen
Guest
 
Posts: n/a
Non-conservativity need not be the cause of failure to converge (in terms of residue fall). There are huge number of finite difference schemes that do give good residue convergence.
  Reply With Quote

Reply


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
how to understand high resolution scheme and high order scheme iilw1314 Main CFD Forum 7 April 12, 2022 13:29
2nd order upwind scheme (Fluent and CFX) Far FLUENT 0 May 22, 2011 02:50
Distributed Parallel on dual core remote machine Justin CFX 1 February 3, 2008 18:23
extrapolation in MUSCL scheme Chandra Main CFD Forum 6 February 14, 2007 12:21
PC vs. Workstation Tim Franke Main CFD Forum 5 September 29, 1999 16:01


All times are GMT -4. The time now is 14:06.