CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   OpenFOAM Running, Solving & CFD (http://www.cfd-online.com/Forums/openfoam-solving/)
-   -   SimpleFoam unable to reach steady state (http://www.cfd-online.com/Forums/openfoam-solving/57888-simplefoam-unable-reach-steady-state.html)

francois January 28, 2009 06:59

Hi Foamers, I'm playing wit
 
Hi Foamers,

I'm playing with the simpleFoam solver for a simple open rotor/stator laminar flow configuration but I'm not able to reach the steady state of the flow.

The angular velocity on the rotor is around 300 tr/min so a Reynolds number (based on the rotor radius) around 2.10^5 is expected. According to the literature the flow is still laminar.

So I try simpleFoam with no turbulence models but even if convergence seems ok I'm not able to reach this steady state. Perhaps the flow is locally turbulent or in transition and a RANS model could be the way to go. Some experiences on those kind of flows ?

Here is one of my last iteration output in the log file:

Time = 95000

DILUPBiCG: Solving for Ux, Initial residual = 0.0114524, Final residual = 0.000374143, No Iterations 2
DILUPBiCG: Solving for Uy, Initial residual = 0.00827667, Final residual = 0.000238708, No Iterations 2
DILUPBiCG: Solving for Uz, Initial residual = 0.00574431, Final residual = 0.000142418, No Iterations 2
DICPCG: Solving for p, Initial residual = 0.0246974, Final residual = 0.000246175, No Iterations 54
time step continuity errors : sum local = 7.81603e-05, global = -2.14943e-06, cumulative = 0.07646
ExecutionTime = 182884 s ClockTime = 183024 s

Any advices to get better convergence to reach the steady state of the flow ?

My setup is as follow:

===========
:fvSchemes:
===========

ddtSchemes
{
default steadyState;
}

gradSchemes
{
default Gauss linear;
grad(p) Gauss linear;
grad(U) Gauss linear;
}

divSchemes
{
default none;
div(phi,U) Gauss upwind;
div(phi,k) Gauss upwind;
div(phi,epsilon) Gauss upwind;
div(phi,R) Gauss upwind;
div(R) Gauss linear;
div(phi,nuTilda) Gauss upwind;
div((nuEff*dev(grad(U).T()))) Gauss linear;
}

laplacianSchemes
{
default none;
laplacian(nuEff,U) Gauss linear corrected;
laplacian((1|A(U)),p) Gauss linear corrected;
laplacian(DkEff,k) Gauss linear corrected;
laplacian(DepsilonEff,epsilon) Gauss linear corrected;
laplacian(DREff,R) Gauss linear corrected;
laplacian(DnuTildaEff,nuTilda) Gauss linear corrected;
}

interpolationSchemes
{
default linear;
interpolate(U) linear;
}

snGradSchemes
{
default corrected;
}

fluxRequired
{
default no;
p;
}

============
:fvSolution:
============

solvers
{
p PCG
{
preconditioner DIC;
tolerance 1e-06;
relTol 0.01;
};
U PBiCG
{
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
};
k PBiCG
{
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
};
epsilon PBiCG
{
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
};
R PBiCG
{
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
};
nuTilda PBiCG
{
preconditioner DILU;
tolerance 1e-05;
relTol 0.1;
};
}

SIMPLE
{
nNonOrthogonalCorrectors 0;
}

relaxationFactors
{
p 0.3;
U 0.7;
k 0.7;
epsilon 0.7;
R 0.7;
nuTilda 0.7;
}


===============
:RASProperties:
===============

RASModel laminar;

turbulence off;

printCoeffs on;

laminarCoeffs
{
}


Thank you very much.
Have a nice day

Francois

francois February 25, 2009 12:33

Hi all, Hopefully I have so
 
5 Attachment(s)
Hi all,

Hopefully I have some time to go back on this case ...

My runs don't reach the steady state and convergence is still not achieved with residuals not so low.

I've attached some pictures to better describe my case. It's a simple rotor/stator configuration with a hole in the stator.

Attachment 42

I've also attached the distribution of the u,v,w velocity components on a radial line between the rotor and stator.

Attachment 43

You can see that steady state is not reach here: one can observe large variation of u,v,w profiles between iteration 80000 and 90000. The behaviour is the same for a greater number of iteration (currently I'm at 120000 iterations).

Below you can see isocontours of the u component around the rotor/stator and one can note a "shear layer" near the rotor which oscillates with iterations (this trend is also observed on the uvw distribution figure just above)

Attachment 47

And to conclude below are the evolution of residuals with the iterations for Ux and Uy for example:

Attachment 46

Attachment 48

So I still have a few questions:

* what is the best procedure to obtain a steady state

* is my computational domain too small (Ddomain = 4rotor and Hdomain = 3Drotor)for this problem with a "feedback" of the outlet boundary condition
?

I will be very pleased to have some advices/ideas frome somone on those points and forgive me for this long post.

Thanks you very much
Regards

Francois

francois February 25, 2009 12:40

Oup's sorry for the images Wi
 
Oup's sorry for the images
Will try again here :

Computationaldomain:



distribution of the u,v,w velocity components on a radial line between the rotor and stator:



u v w contours:





Residuals:











francois February 25, 2009 12:50

Humm ... sorry Don't work her
 
Humm ... sorry
Don't work here with firefox 3.06 on ubuntu 8.10

What the best way to send/attach picture or files on the message board ?
I use:

\ image{foo} or \ attach{foo} with no space between \ and the after word

It seems that I always have to struggle until death to be able to send some files or images here.

andersking February 25, 2009 23:46

I think your syntax is probabl
 
I think your syntax is probably fine, but there's a very small limit on image sizes, 50K I think. It doesn't stop you from posting, but won't show the images.

Less than 50K is fine.

Cheers
Andrew

francois February 26, 2009 06:18

Thanks Andrew for your advice
 
Thanks Andrew for your advice

But my images sizes are always under 50k and I never saw the dialog for file upload

So the problem seems to be elsewhere ...

Cheers
Francois

andersking February 27, 2009 01:19

Hmmm, hopefully it will all ge
 
Hmmm, hopefully it will all get betted with the new forum software.

Cheers
Andrew

francois March 18, 2009 16:59

I've just modified the first post and was able to include some of the images which could not be posted in the last forum...

Yeah ... the new forum is better :D

novyno November 19, 2009 14:33

Same problem too...
 
I have the same convergence problem... Can someone help us?


All times are GMT -4. The time now is 19:47.