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

star cd convergence error

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

Reply
 
LinkBack Thread Tools Display Modes
Old   September 14, 2011, 04:16
Default star cd convergence error
  #1
New Member
 
Join Date: Mar 2011
Posts: 11
Rep Power: 6
gagi is on a distinguished road
hi im a chemical engineering post graduate student and i have to model and simulate a tray dryer using STAR CD and im somewhat new to CFD. i started my model as a .IGES file and created the surface mesh in pro-surf as a .dbs file n then as a .mdl file in pro amm. when i run the model there are convergence errors and when i check the residuals and browse the standard output file, after 2 iterations there is an error message saying,
"FLUID FLOW DETECTED AT SOME OUTFLOW BOUNDARIES MASS FLUX IS FORCED TO ZERO. IF THIS CONDITION PERSISTS, YOUR CALCULATIONS MAY BE WRONG "

the mesh didn't get converged after 100000 iterations. my mesh got around 1 500 000 fluid (air) trimmed cells, with 5ms-1 air speed at the inlet and flow is steady state and laminar. used SIMPLE method to solve it. and in the star guide panel, i make all the input parameters like i did in the STAR tutorial 2nd example, (flow in a partially blocked elbow).

im new to CFD and STAR CD and spend considerable time to figure out whats wrong with my model .. can you please give me some advice?
gagi is offline   Reply With Quote

Old   September 14, 2011, 08:14
Default
  #2
Member
 
Robert
Join Date: Jun 2010
Posts: 86
Rep Power: 8
RobertB is on a distinguished road
You probably have a recirculation zone hitting the exit boundary (from the error messages).

Either that or you have a problem that does not have a steady state solution, are the residuals moving cyclically?
RobertB is offline   Reply With Quote

Old   September 14, 2011, 10:17
Default
  #3
New Member
 
Join Date: Mar 2011
Posts: 11
Rep Power: 6
gagi is on a distinguished road
hi, thanks for replying.

i think you are correct. when i apply initial conditions, i used 1 atm as inlet in refernce pressure cell so flow may probably flows inward at the outlet as static pressure + dynamic pressure at outlet is greater than the inlet pressure. thanks a lot. il try it again for actual pressure.
can i select a cell form outlet boundary as a refernce pressure cell?

yaaa there were cyclic residuals and mass flux residual is circulating near 1 and other velocity u, v and w components are circulating near 0.01 and below.. i used 0.001 as the maximum residual tolarance.
initially im trying to model the air flow and later going to modify mesh to obtain uniform velocity distribution. as only air at 20 C temperature is involved i took it as steady state and SIMPLE mode (even PISO and SIMPSO did not give converged solution)


thanks again. tc
gagi is offline   Reply With Quote

Old   September 14, 2011, 11:15
Default
  #4
Member
 
Robert
Join Date: Jun 2010
Posts: 86
Rep Power: 8
RobertB is on a distinguished road
You can use any cell as your reference if you do not have pressure boundaries in the model. It only really has any real effect if your are running a compressible fluid (i.e. ideal gas).

Typically plotting up the flow field gives you a pretty good idea as to what is going wrong (even if unconverged).
RobertB 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
Compile calcMassFlowC aurore OpenFOAM Programming & Development 12 March 18, 2014 05:22
How to install CGNS under windows xp? lzgwhy Main CFD Forum 1 January 11, 2011 19:44
CGNS lib and Fortran compiler manaliac Main CFD Forum 2 November 29, 2010 07:25
compile errors of boundary condition "expDirectionMixed" liying02ts OpenFOAM Bugs 2 February 1, 2010 21:11
Installation of Netgen in SuSE Linux 92 edvardsenpriv Open Source Meshers: Gmsh, Netgen, CGNS, ... 23 January 16, 2009 07:12


All times are GMT -4. The time now is 11:58.