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September 5, 2012, 05:30 
Problem with divergence

#1 
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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 
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Stuart Buckingham
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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
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September 5, 2012, 09:40 

#3 
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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 
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Stuart Buckingham
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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
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September 5, 2012, 10:26 

#5 
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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 
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Maybe try decreasing the Turbulent Viscosity UnderRelaxation Factor. Also could try higher order schemes for turbulence terms.
What pv scheme are you using? Stu
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September 5, 2012, 11:35 

#7 
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Yon Han Chong
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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 
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Prakash Ghose
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# 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 
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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 
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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 
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Stuart Buckingham
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Could be due to huge gradients across adjacent cells. Try refining around your body and using higher order numerics for turbulence.
Stu
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