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

Convergence Problem

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 10, 2012, 06:49
Default Convergence Problem
  #1
New Member
 
Roblad's Avatar
 
Rob Hulme
Join Date: Jan 2012
Location: UK
Posts: 3
Rep Power: 5
Roblad is on a distinguished road
Hi, I am simulating an induced air flow system where air from a compartment is drawn out using exhaust gases. The values for the inlet conditions (Mass flow rate Kg/s and density Kg/m3) have been determined using an experiment.

I have now ran numerous iterations but the model is not converging. An image of the model is attached.

I am guessing the probe position and number of iterations are the main factors. I am using a SARAH value of 0.001 to try and aid the convergence.

Any advice would be greatly appreciated.
Attached Images
File Type: jpg Simulation.jpg (27.0 KB, 60 views)
Roblad is offline   Reply With Quote

Old   April 10, 2012, 13:04
Default Latest Run: 1000 Iteration Result
  #2
New Member
 
Roblad's Avatar
 
Rob Hulme
Join Date: Jan 2012
Location: UK
Posts: 3
Rep Power: 5
Roblad is on a distinguished road
Hi, I have just ran a 1000 iteration simulation and again there is no sign of convergence.

I gather from the results the probe position needs to be changed as there is a fluctution in all the variables in this position.

The velocity values at the inlet are incorrect, the inlet condition is 0.04Kg/s but the model reads a velocity of 70,438m/s at the inlet where a value of around 10m/s is anticipated.

Would this error be caused due to the lack of convergence?
Roblad is offline   Reply With Quote

Old   April 17, 2012, 11:47
Default
  #3
Senior Member
 
Julio Mendez
Join Date: Apr 2009
Location: Greensboro, U.S.A
Posts: 106
Rep Power: 8
juliom is on a distinguished road
Send a message via Skype™ to juliom
It seems to be a boundary condition problem!!! why don`t you explain your problem in more details!!!
Godd luck!
juliom is offline   Reply With Quote

Old   April 19, 2012, 08:30
Default
  #4
New Member
 
Join Date: Apr 2012
Posts: 5
Rep Power: 5
marco100 is on a distinguished road
Hi,
The cause of a convergence problem can be anything (grid problem, setting of underrelaxation parameters, etc. etc.). Sometimes it helps if
you make it a time dependent run with small time steps until the solution
is stable.
marco100 is offline   Reply With Quote

Old   April 25, 2012, 23:52
Default
  #5
New Member
 
mj
Join Date: Apr 2010
Posts: 5
Rep Power: 7
doctor evil is on a distinguished road
Try checking the flow pattern at the outlet, there might be a strong recirculation. If so, try to enlarge your domain. though, it is not easy to solve such a problem in phoenics.
And is this problem isothermal or not? If not, the relaxation factor is also one possible reason for divergence.
good luck
doctor evil 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
convergence problem when use pisoFoam, LES for wind tunnel case Forrest_Lei OpenFOAM 3 July 19, 2011 06:00
convergence problem commonyue Main CFD Forum 1 December 1, 2009 04:54
Convergence of CFX field in FSI analysis nasdak CFX 2 June 29, 2009 01:17
3D Fluid Flow Convergence problem Emily FLUENT 2 March 21, 2007 23:18
Non Convergence of 3D Heat transfer cfd problem Balraj Main CFD Forum 3 December 9, 2004 01:24


All times are GMT -4. The time now is 14:17.