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-   -   bounding epsilon blow up (http://www.cfd-online.com/Forums/openfoam-solving/80609-bounding-epsilon-blow-up.html)

jiez September 30, 2010 11:42

bounding epsilon blow up
 
It is a case using simpleFoam solver with K-epsilon Turbulence model.

the fellowing result will blow up. Is there anyone can help me to find out where the problem comes from? BC setting('epsilo' attached)?

Time = 0.001
DILUPBiCG: Solving for Ux, Initial residual = 0.64936, Final residual = 0.0285001, No Iterations 1
DILUPBiCG: Solving for Uy, Initial residual = 0.527993, Final residual = 0.0462129, No Iterations 1
DILUPBiCG: Solving for Uz, Initial residual = 0.815427, Final residual = 0.0168725, No Iterations 2
DICPCG: Solving for p, Initial residual = 1.42064e-15, Final residual = 1.42064e-15, No Iterations 0
time step continuity errors : sum local = 6.86127e+27, global = 7.64441e+11, cumulative = -2.2062e+23
DILUPBiCG: Solving for epsilon, Initial residual = 4.35678e-07, Final residual = 4.35678e-07, No Iterations 0
bounding epsilon, min: 3.3635e-22 max: 1.18516e+87 average: 7.77262e+80
DILUPBiCG: Solving for k, Initial residual = 5.98618e-09, Final residual = 5.98618e-09, No Iterations 0
ExecutionTime = 193.75 s ClockTime = 195 s



BC setting:

epsilo:

wall
{
type epsilonWallFunction;
Cmu 0.09;
kappa 0.41;
E 9.8;
value uniform 0.0012;
}

inlet
{
type fixedValue;
value uniform 0.0012;
}

outlet
{
type zeroGradient;
}

jiez September 30, 2010 11:46

I'm new to FOAM.
I will be very appreciated for your help!

santiagomarquezd September 30, 2010 20:07

Maybe a draft of the geometry, details of problem and

system/controlDict
system/fvSchemes
system/dvSolution
0/*

dictionaries can give us a better idea how to solve the blowing up.

Regards.

tcarrigan October 8, 2010 17:11

Try setting the k and e schemes to upwind rather than linear in the fvSchemes directory. I've had problems achieving convergence using second order schemes for the turbulence models.

kroetenechse January 16, 2011 18:14

In my case it was a great help to reduce the relaxation factors. I had the same problem. The relaxation factors are responsible for the search of a the start value in the calculation of the parameters depending of the result in the last time step. If you reduce them, the start value is not so far away to the last result but youŽll need more time for the calculation.

Try it. You find the relaxationFactors in fvSolution and then reduce all factors 0.1 down. If it doesnŽt help, try 0.2.

It could be the geometry, too. But try it.
Hope, it helps.
greetz phil


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