
[Sponsors] 
September 5, 2012, 05:30 
Problem with divergence

#1 
New Member
T
Join Date: Sep 2012
Posts: 7
Rep Power: 5 
I'm trying to model a single wheel in free stream air within fluent.
I'm using the realizable kepsilon turbulence model but when I run my calculation for around 20 iterations, at around the 6th one it says: 'Divergence detected in AMG solver: epsilon' Anyone got any ideas on what this means? I'd much appreciate the help! 

September 5, 2012, 07:41 

#2 
Senior Member
Stuart Buckingham
Join Date: May 2010
Location: United Kingdom
Posts: 267
Rep Power: 16 
If you are sure your case is set up right, try the following:
Do a mesh check. Is your skewness acceptable? Boundary Conditions. Are your k & e values suitable. http://support.esicfd.com/esiusers/turb_parameters/ Initialization. Try the hybrid (FMG) initialization. Underrelaxation Factors. try using 0.5 for both k & e, then ramp them up to 0.9 after 50~100 iterations. Also decrease timestep or Courant Number (dependent on solver) Hopefully one of these will work Stu
__________________
http://bc247.wordpress.com 

September 5, 2012, 09:40 

#3 
New Member
T
Join Date: Sep 2012
Posts: 7
Rep Power: 5 
Thanks alot Stu, it worked
but now, after around 12 iterations, i get the message, turbulent viscosity limited to viscosity ratio of 1.000000e+05 in (a number) cells And that message just keeps appearing for every iteration after the 12th one or so. 

September 5, 2012, 10:17 

#4 
Senior Member
Stuart Buckingham
Join Date: May 2010
Location: United Kingdom
Posts: 267
Rep Power: 16 
Does the number of cells it occurs in decrease? Also, which of the above solutions caused your simulation to run?
Maybe try turning on wall functions. You will find this in your turbulence settings
__________________
http://bc247.wordpress.com 

September 5, 2012, 10:26 

#5 
New Member
T
Join Date: Sep 2012
Posts: 7
Rep Power: 5 
erm my skewness and mesh was fine so I just tried out the initialization, because im following up some work that was done before and I am trying to keep the boundary conditions the same as the work done before.
Also the number of cells it occurs in increases. 

September 5, 2012, 10:47 

#6 
Senior Member
Stuart Buckingham
Join Date: May 2010
Location: United Kingdom
Posts: 267
Rep Power: 16 
Maybe try decreasing the Turbulent Viscosity UnderRelaxation Factor. Also could try higher order schemes for turbulence terms.
What pv scheme are you using? Stu
__________________
http://bc247.wordpress.com 

September 5, 2012, 11:35 

#7 
Member
Yon Han Chong
Join Date: Jun 2012
Posts: 77
Rep Power: 5 
In material, what are you using for the air? If you are running incompressible then are you using incompressible ideal gas for the density?


September 6, 2012, 01:57 

#8 
New Member
Prakash Ghose
Join Date: Dec 2011
Posts: 29
Rep Power: 5 
# Divergence detected in AMG solver: wswirl > Increasing relaxation sweeps!
Divergence detected in AMG solver: wswirl Divergence detected in AMG solver: k Divergence detected in AMG solver: epsilon Divergence detected in AMG solver: wswirl Divergence detected in AMG solver: k Divergence detected in AMG solver: epsilon Divergence detected in AMG solver: wswirl Divergence detected in AMG solver: k Divergence detected in AMG solver: epsilon Divergence detected in AMG solver: wswirl Divergence detected in AMG solver: k Divergence detected in AMG solver: epsilon Primitive Error at Node 0: floating point exception Primitive Error at Node 1: floating point exception Primitive Error at Node 2: floating point exception Primitive Error at Node 3: floating point exception Error: floating point exception Error Object: #f any body help me? 

September 6, 2012, 04:32 

#9 
New Member
T
Join Date: Sep 2012
Posts: 7
Rep Power: 5 
when i tried turnin the wall function on, after 95 iterations or so i get this message again..
Error: Divergence detected in AMG solver: epsilon Error Object: #f and the pv scheme is the simplec method 

September 6, 2012, 05:59 

#10 
New Member
T
Join Date: Sep 2012
Posts: 7
Rep Power: 5 
Calculating the solution...
iter continuity xvelocity yvelocity zvelocity k epsilon cl cd time/iter 10 3.2734e01 3.0660e04 1.1532e03 1.9049e03 4.5918e02 3.2611e01 3.1384e03 7.0838e03 0:26:06 40 turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 75 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 37 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 44 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 55 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 70 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 76 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 84 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 90 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 100 cells 20 1.8165e01 3.1788e04 9.4947e04 1.2923e03 6.6196e02 9.0918e02 5.8485e03 6.6261e04 0:18:44 30 turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 113 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 87 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 106 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 110 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 110 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 110 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 119 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 116 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 115 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 108 cells 30 1.6222e01 1.1946e03 1.1032e03 1.3504e03 2.6384e01 3.9193e01 9.1864e03 4.6980e03 0:12:29 20 turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 103 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 107 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 108 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 114 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 117 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 116 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 116 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 116 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 113 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 112 cells 40 1.7292e01 6.6118e04 9.4381e04 1.1887e03 6.4812e02 1.8510e01 9.7351e03 1.0745e02 0:06:10 10 turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 112 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 117 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 116 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 115 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 117 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 117 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 116 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 116 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 117 cells turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 114 cells 50 1.7279e01 6.0444e04 8.8136e04 1.1025e03 3.0306e02 6.1610e02 9.8257e03 2.0159e02 0:00:00 0 Calculation complete. Interrupting... Done. I'm still getting this same error...any ideas on what it could be :S 

September 8, 2012, 01:11 

#11 
Senior Member
Stuart Buckingham
Join Date: May 2010
Location: United Kingdom
Posts: 267
Rep Power: 16 
Could be due to huge gradients across adjacent cells. Try refining around your body and using higher order numerics for turbulence.
Stu
__________________
http://bc247.wordpress.com 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Meshing and divergence problem  ghost  FLUENT  9  February 5, 2010 13:24 
divergence problem  vincent  FLUENT  3  August 3, 2006 15:44 
strange divergence when solving multiphase problem  tanghao  FLUENT  2  July 27, 2006 19:47 
divergence problem  Ayyappan.T  FLUENT  2  May 16, 2005 12:10 
help:spectral methods & divergence free functionsn  D. Puigjaner  Main CFD Forum  1  August 28, 2000 10:06 