|
[Sponsors] |
July 7, 2017, 08:56 |
time step continuity errors
|
#1 | ||
New Member
rmz
Join Date: May 2017
Location: Paris
Posts: 12
Rep Power: 9 |
hello,
I am working on a simulation of wind on buildings with a complex Mesh. I am using a RASModel kEspilon with the simpleFoam solver. I am applying ABL conditions (atmospheric boundary layer). I am facing problems with the solution convergence. the following is the begining of the output of simpleFoam: Quote:
Quote:
sum local = 1.92360928162e+41, global = -3.25979779589e+25, cumulative = -3.25979779589e+25 I am trynig to understand the meaning of "time step continuity errors". I searches the forum but didn't find a clear description. What are the possible solutions to this problem. thank you |
|||
July 9, 2017, 08:17 |
|
#2 |
Senior Member
khedar
Join Date: Oct 2016
Posts: 111
Rep Power: 10 |
Why don't you act on the warning issued by the solver,
Code:
Time = 1401 --> FOAM Warning : From function Foam::fv::gaussConvectionScheme<Type>::gaussConvec tionScheme(const Foam::fvMesh&, const surfaceScalarField&, Foam::Istream&) [with Type = Foam::Vector<double>; Foam::surfaceScalarField = Foam::GeometricField<double, Foam::fvsPatchField, Foam::surfaceMesh>] in file finiteVolume/convectionSchemes/gaussConvectionScheme/gaussConvectionScheme.H at line 124 Reading "/home/ingerop/OpenFOAM/ingerop-4.1/run_Dell/PAP_run/PAP_case_06_30/system/fvSchemes.divSchemes.div(phi,U)" at line 32 Unbounded 'Gauss' div scheme used in steady-state solver, use 'bounded Gauss' to ensure boundedness. Also I see your k and epsilon are being bounded at before the actual start of the simulation itself. See here Code:
Reading/calculating face flux field phi Selecting incompressible transport model Newtonian Selecting turbulence model type RAS Selecting RAS turbulence model kEpsilon bounding k, min: 0 max: 46.975528397 average: 1.29999999999 bounding epsilon, min: 0 max: 173.377103808 average: 0.0100000000001 kEpsilonCoeffs { Cmu 0.09; C1 1.44; C2 1.92; sigmaEps 1.11; C3 -0.33; sigmak 1; } |
|
July 11, 2017, 06:29 |
|
#3 | |
New Member
rmz
Join Date: May 2017
Location: Paris
Posts: 12
Rep Power: 9 |
Hello Khedar,
thank you very musch for your answer. -concerning the divScheme for (phi, U): the old one was "Gauss limitedLinear 1". I chaned it to "bounded Gauss limitedLinear 1". I searched online and I found that this scheme could solve the time step continuity error. Do you have any suggestions concerning the schemes? -Concerning my mesh: I checked my Mesh with the checkMesh utility and obtained bad results: Quote:
is there any utilities or parameters to change that can improve the mesh quality? Also could you explain to me please which problems in the mesh are causing the bounding k and epsilon and why? thank you for your help, rmz |
||
July 12, 2017, 09:49 |
accuracy of simpleFoam - bounding epsilon/k
|
#4 | |
New Member
rmz
Join Date: May 2017
Location: Paris
Posts: 12
Rep Power: 9 |
Hello,
I searched for schemes that can fix my bounding K and bounding epsilon problem. I tried several simulations, and found a modification that improved my simulation: changing "laplacianSchemes" from "Gauss linear limited 1" to Gauss linear limited 0.333 changing "snGradSchemes" from "limited 1" to limited 0.333 simpleFoam ran for 800 steps before the "bounding k" / "bounding epsilon" warning appears. the following is an output from the last steps of simpleFoam: Quote:
I am only interested in the results of p and U, and not interested in epsilon and k. simpleFoam is stable and converging. my question is: -is simpleFoam converging to a correct solution (for p and U)? -what is the accuracy of p and U results, does the bounding k and epsilon problem influence the results too much? thank you |
||
July 12, 2017, 12:16 |
|
#5 |
Senior Member
khedar
Join Date: Oct 2016
Posts: 111
Rep Power: 10 |
I would say its not right to assume that your results are good when you have bad values for some of your variables(k and Epsilon). You should definitely improve your mesh with respect to skewness. It looks very bad. One cannot stress enough on spending more time in creating a good quality mesh to avoid problems later on.
|
|
Tags |
bounding epsilon, bounding k, simplefoam convergence, skewness, time step continuity |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
High Courant Number @ icoFoam | Artex85 | OpenFOAM Running, Solving & CFD | 11 | February 16, 2017 14:40 |
Floating point exception error | lpz_michele | OpenFOAM Running, Solving & CFD | 53 | October 19, 2015 03:50 |
InterFoam negative alpha | karasa03 | OpenFOAM | 7 | December 12, 2013 04:41 |
IcoFoam parallel woes | msrinath80 | OpenFOAM Running, Solving & CFD | 9 | July 22, 2007 03:58 |
Could anybody help me see this error and give help | liugx212 | OpenFOAM Running, Solving & CFD | 3 | January 4, 2006 19:07 |