CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

Problem with simpleFoam

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 21, 2011, 10:02
Default Problem with simpleFoam
  #1
Member
 
Join Date: Oct 2010
Location: Naples
Posts: 50
Rep Power: 6
salvoblack is on a distinguished road
Dear foamers, i have a problem.
Every time I do a calculation with simpleFoam, I have problems related to the type of mesh used. In fact, using an airfoil, if I use a fairly low number of cells as 20,000 I get acceptable results, but if my airfoil is thicker (70000) of the cells i have completely absurd results : the solution diverges. I do not change anything between the various settings, change only the mesh. could you tell me if there is a parameter that should be changed depending on the quality of the mesh??
salvoblack is offline   Reply With Quote

Old   March 21, 2011, 11:22
Default
  #2
Senior Member
 
Mirko Vukovic
Join Date: Mar 2009
Posts: 159
Rep Power: 8
mirko is on a distinguished road
Quote:
Originally Posted by salvoblack View Post
Dear foamers, i have a problem.
Every time I do a calculation with simpleFoam, I have problems related to the type of mesh used. In fact, using an airfoil, if I use a fairly low number of cells as 20,000 I get acceptable results, but if my airfoil is thicker (70000) of the cells i have completely absurd results : the solution diverges. I do not change anything between the various settings, change only the mesh. could you tell me if there is a parameter that should be changed depending on the quality of the mesh??
You may have to decrease the time step. Check your courant number.
mirko is offline   Reply With Quote

Old   March 22, 2011, 05:41
Default
  #3
Member
 
Join Date: Oct 2010
Location: Naples
Posts: 50
Rep Power: 6
salvoblack is on a distinguished road
Hello,
I use the cam to calculate the Co courant in openFoam?
salvoblack is offline   Reply With Quote

Old   March 22, 2011, 06:15
Default
  #4
Senior Member
 
maddalena's Avatar
 
maddalena
Join Date: Mar 2009
Posts: 436
Rep Power: 12
maddalena is on a distinguished road
Quote:
Originally Posted by mirko View Post
You may have to decrease the time step. Check your courant number.
If using simpleFoam the Co is useless, since the simulation is steady state!
Salvo, could you post checkMesh of the old (coarse) mesh and the new (finest) mesh? How do you made the refinement? Increasing the cell number does not mean that you improve mesh quality!!!
What about y+ values?
Have you try to see where the problem may be using simpleFoamResiduals?

mad
maddalena is offline   Reply With Quote

Old   March 22, 2011, 10:23
Default
  #5
Member
 
Join Date: Oct 2010
Location: Naples
Posts: 50
Rep Power: 6
salvoblack is on a distinguished road
hi maddalena,sorry for my english.
i put in the terminal Co so i have the Courant number for my mesh.
I have a very very high value of this number:6*10^6. i think that this is the problem for my case.
i know that i can impose Co=1 knowing the distance between cells and the time step. How can I calculate these factors for my mesh???I don't know how calcolate the distance between cells
thanks
salvoblack is offline   Reply With Quote

Old   March 22, 2011, 17:01
Default
  #6
Senior Member
 
maddalena's Avatar
 
maddalena
Join Date: Mar 2009
Posts: 436
Rep Power: 12
maddalena is on a distinguished road
Hi Salvo,
Quote:
Originally Posted by salvoblack View Post
hi maddalena,sorry for my english.
i put in the terminal Co so i have the Courant number for my mesh.
I have a very very high value of this number:6*10^6. i think that this is the problem for my case.
i know that i can impose Co=1 knowing the distance between cells and the time step. How can I calculate these factors for my mesh???I don't know how calcolate the distance between cells
thanks
your English is not a big issue as far as I can understand your problem.
However... are you really using simpleFoam? If so, than Co has no meaning at all! See equation 2.2 here In your case you should have set deltaT=1, since simpleFoam is a steady state solver, thus deltaT is an iteration counter only! If you want, delete the maxCo line in controlDict file. simpleFoam should no complain about this missing entry, since it does not need it.
In conclusion: the problem lies somewhere else...

mad
maddalena is offline   Reply With Quote

Old   March 23, 2011, 03:54
Default
  #7
Member
 
Join Date: Oct 2010
Location: Naples
Posts: 50
Rep Power: 6
salvoblack is on a distinguished road
thank you for yor help, maddalena. i decided to re-make the mesh!!!
just a curiosity, are you italian??
salvoblack is offline   Reply With Quote

Old   March 23, 2011, 03:56
Default
  #8
Senior Member
 
maddalena's Avatar
 
maddalena
Join Date: Mar 2009
Posts: 436
Rep Power: 12
maddalena is on a distinguished road
Quote:
Originally Posted by salvoblack View Post
thank you for yor help, maddalena. i decided to re-make the mesh!!!
just a curiosity, are you italian??
Yes, I am. That is probably way I can understand your english easily: it is similar to mine!


mad
maddalena 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
UDF compiling problem Wouter Fluent UDF and Scheme Programming 6 June 6, 2012 04:43
Can I solve this problem by Fluent? Kai_kc FLUENT 1 October 27, 2010 05:29
natural convection problem for a CHT problem Se-Hee CFX 2 June 10, 2007 06:29
Adiabatic and Rotating wall (Convection problem) ParodDav CFX 5 April 29, 2007 19:13
Is this problem well posed? Thomas P. Abraham Main CFD Forum 5 September 8, 1999 14:52


All times are GMT -4. The time now is 14:19.