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

CFX vs. CFDesign

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

Reply
 
LinkBack Thread Tools Display Modes
Old   September 21, 2010, 04:14
Default
  #21
New Member
 
JohnParry's Avatar
 
John Parry
Join Date: Mar 2009
Posts: 12
Rep Power: 7
JohnParry is on a distinguished road
Narender,
You said above "My main concern is the CFdesign code does not maintain the steady state such as not maintain equal in and out flow rates (at inlet and outlet)." If you've not been able to fix that I would ignore the CFdesign results. However, assuming you have, and you've checked you've got a good mass balance in both codes I'd look carefully at the differences in the solutions to see if either exhibit any non-physical behaviour based on your engineering knowledge. Beyond that I'd coarsen the mesh in both cases and look to see how the results change to get a feel for which code is giving you results that are closest to mesh independent. You may be a long way off with first order on a tet mesh. I'd be inclined to go with the result that's the least mesh dependent. You could look at overall pressure drop as a measure of mesh independence. Hope that helps,
__________________
Dr John Parry, CEng CITP
Electronics Industy Manager
Mecahnical Analysis Division
Mentor Graphics Corporation
JohnParry is offline   Reply With Quote

Old   February 9, 2012, 16:49
Default
  #22
New Member
 
anonymous
Join Date: Feb 2012
Posts: 1
Rep Power: 0
sbarthelson is on a distinguished road
Hi,

What I think is behind differences between CFX and Cfdesign is that Cfdesign uses the SIMPLE or SIMPLER algorithms and segregated solvers, which were state of the art in the late 80s. CFX on the other hand uses multigrid and a powerful coupled solver developed in the mid 90s. In brief I believe that the result is better converged equations.

What is especially uncomfortable about Cfdesign is the criteria it uses for convergence -it looks at plateauing of residuals as opposed to how many orders of magnitude their size has been reduced. I don't think this correct.

best of wishes,

Steve
sbarthelson is offline   Reply With Quote

Old   February 9, 2012, 19:49
Default
  #23
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 9,551
Rep Power: 76
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
The coupled solver in CFX is frequently a good thing for steady state runs where it allows convergence in far less iterations than an uncoupled solver. But for transient runs an uncoupled solver is often faster as the small time steps required by a transient run mean the weaker p-v coupling in an uncoupled solver is more than compensated by the much faster time per coefficient loop.

But there are exceptions to these general principles as well - really you need to compare it for your specific case as it is case by case as to which is best.
ghorrocks is offline   Reply With Quote

Reply

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
Pros and Cons for CFX, CFdesign, COMSOL Val Main CFD Forum 3 June 10, 2011 02:20
FloEFD CFDesign or CFX Bigga CFX 4 January 4, 2010 06:41
CFX or CFDesign Ed Chavez Main CFD Forum 8 October 18, 2007 04:26
PhD using CFX Rui CFX 9 May 28, 2007 05:59
CFDesign > CFX or ICEM CFD Endlos CFX 0 June 14, 2005 02:55


All times are GMT -4. The time now is 12:06.