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-   -   Convergence with MRFSimpleFoam (http://www.cfd-online.com/Forums/openfoam-solving/58776-convergence-mrfsimplefoam.html)

grugg October 3, 2007 12:13

Hi all, I have created a thre
 
Hi all,
I have created a three-dimensional fuel rotating pump leaving from the MRFSimpleFoam tutorial in OpenFoam-1.4.1. There are two regions, one cylindrical inner that rotates at 720 rad/s and one external fixed. They are connected with three interfaces ggi: one on top, one lateral and one on bottom. There is also inlet and outlet.
The MRFZones are defined like in the tutorial with rotor and stator.
After one timeStep the residual value increse and I don't know why.
I have tried the mixer2d icoDyMFoam tutorial and a lot of other cases with this method and they work very well.
Here there are the log file, p, U and MRFZones

/*---------------------------------------------------------------------------*\
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 1.4.1 |
| \ / A nd | Web: http://www.openfoam.org |
| \/ M anipulation | |
\*---------------------------------------------------------------------------*/

Exec : MRFSimpleFoam . pump
Date : Oct 03 2007
Time : 15:22:47
Host : sarge
PID : 27336
Root :
/gamma/grugg/OpenFOAM/OpenFOAM-1.4.1/tutorials/MRFSimpleFoam
Case : pump
Nprocs : 1
Create time

Create mesh for time = 0

Reading field p

Reading field U

Reading/calculating face flux field phi

Selecting incompressible transport model Newtonian
Selecting turbulence model laminar

Starting time loop

Time = 1

smoothSolver: Solving for Ux, Initial residual = 0, Final residual = 0, No Iterations 1
smoothSolver: Solving for Uy, Initial residual = 0, Final residual = 0, No Iterations 1
smoothSolver: Solving for Uz, Initial residual = 0, Final residual = 0, No Iterations 1
PCG: Solving for p, Initial residual = 1, Final residual = 9.85725e-07, No Iterations 767
PCG: Solving for p, Initial residual = 0.00230797, Final residual = 9.98469e-07, No Iterations 148
PCG: Solving for p, Initial residual = 0.000382438, Final residual = 9.98736e-07, No Iterations 297
PCG: Solving for p, Initial residual = 8.68112e-05, Final residual = 9.9683e-07, No Iterations 15
PCG: Solving for p, Initial residual = 2.74264e-05, Final residual = 9.87837e-07, No Iterations 8
time step continuity errors : sum local = 4.03381, global = -0.0905555, cumulative = -0.0905555
ExecutionTime = 91.13 s ClockTime = 92 s

Time = 2

smoothSolver: Solving for Ux, Initial residual = 0, Final residual = 0, No Iterations 1
smoothSolver: Solving for Uy, Initial residual = 0, Final residual = 0, No Iterations 1
smoothSolver: Solving for Uz, Initial residual = 0, Final residual = 0, No Iterations 1
PCG: Solving for p, Initial residual = 0.997299, Final residual = 0.393761, No Iterations 7000

*---------------------------------------------------------------------------*\
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 1.4.1 |
| \ / A nd | Web: http://www.openfoam.org |
| \/ M anipulation | |
\*---------------------------------------------------------------------------*/

FoamFile
{
version 2.0;
format ascii;

root "";
case "";
instance "";
local "";

class volScalarField;
object p;
}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //


dimensions [0 2 -2 0 0 0 0];

internalField uniform 106000;

boundaryField
{
inlet
{
type totalPressure;
p0 uniform 106000;
U U;
phi phi;
rho none;
psi none;
gamma 1.0;
}

outlet
{
type outletInlet;
outletValue uniform 106066;
}

rotor
{
type zeroGradient;
}

stator
{
type zeroGradient;
}

outsideSliderTop
{
type ggi;
}

outsideSliderBottom
{
type ggi;
}

outsideSliderLateral
{
type ggi;
}

insideSliderTop
{
type ggi;
}

insideSliderBottom
{
type ggi;
}

insideSliderLateral
{
type ggi;
}
}


// ************************************************** *********************** //

/*---------------------------------------------------------------------------*\
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 1.4.1 |
| \ / A nd | Web: http://www.openfoam.org |
| \/ M anipulation | |
\*---------------------------------------------------------------------------*/

FoamFile
{
version 2.0;
format ascii;

root "/gamma/grugg/OpenFOAM/OpenFOAM-1.4.1/tutorials/MRFSimpleFoam";
case "pompaGRUGG_2";
instance "0";
local "";

class volVectorField;
object U;
}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 1 -1 0 0 0 0];

internalField uniform (0 0 0);

boundaryField
{
rotor
{
type fixedValue;
value uniform (0 0 0);
}
insideSliderTop
{
type ggi;
value uniform (0 0 0);
}
insideSliderLateral
{
type ggi;
value uniform (0 0 0);
}
insideSliderBottom
{
type ggi;
value uniform (0 0 0);
}
stator
{
type fixedValue;
value uniform (0 0 0);
}
outsideSliderTop
{
type ggi;
value uniform (0 0 0);
}
outsideSliderLateral
{
type ggi;
value uniform (0 0 0);
}
outsideSliderBottom
{
type ggi;
value uniform (0 0 0);
}
inlet
{
type pressureInletVelocity;
value uniform (0 0 0);
}

outlet
{
type inletOutlet;
inletValue uniform (0 0 0);
}
}


// ************************************************** *********************** //

/*---------------------------------------------------------------------------*\
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 1.4.1 |
| \ / A nd | Web: http://www.openfoam.org |
| \/ M anipulation | |
\*---------------------------------------------------------------------------*/

FoamFile
{
version 2.0;
format ascii;

root "";
case "";
instance "";
local "";

class dictionary;
object MRFZones;
}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

1
(
rotor
{
patches (rotor);
origin origin [0 1 0 0 0 0 0] (0 0 0);
axis axis [0 0 0 0 0 0 0] (0 0 1);
omega omega [0 0 -1 0 0 0 0] 720;
}
)

// ************************************************** *********************** //



First region, omega = 720 rad/s

rotor (blades)

insideSliderTop

insideSliderLateral

insideSliderBottom

Second region, fixed

stator (external wall)

outsideSliderTop

outsideSliderLateral

outsideSliderBottom

inlet

outlet

Please can anyone help me ?
I'm sorry, my english is not good.
Thanks

Gabriele

waynezw0618 March 29, 2008 11:07

hi: have you ever resolve yo
 
hi:
have you ever resolve your problem?try to modify the initial condition?

david June 26, 2008 10:02

MRFSimpleFoam computes relativ
 
MRFSimpleFoam computes relative fluxes for the cell faces of the rotating frame. The affected faces are listed in faceZones. I assume that the flux is treated as absolute for the control surfaces of the ggi interface. Does anybody know it more precisely and how would it be possible to make the fluxes relative at the interface?

Regards
david

aldo.iannetti June 19, 2010 12:27

MRFSimpleFoam 2nd order convergence
 
2 Attachment(s)
Hi
I'm trying to simulate a 3D cooling fan using OF 1.6 and MRFSimpleFoam, I'm interested in a second order upwind solution.
My grid is 3D, unstructured, tetraedral and imported from GAMBIT. The rotational velocity has been given step by step growing from 50 rad/s to 272 rad/s. Residuals go down till 4000 iterations after that they start to increase and diverge. Here attached my fvSchemes and the log file.
Can you please give me advices about settings (under relaxation, discretization schemes etc..)
Thanks

hm86 July 19, 2010 23:16

Convergence issues
 
I am running MRFSimpleFoam on a wind turbine blade using the Spallart-Allmaras turbulence model. I am using inletOutlet BCs on p, U, rho and fixedValues of nut and nuTilda on the outer boundary but after 300 iterations the residuals begin to diverge and eventually blow up. Has anyone seen this before or have any idea why this is happening?

skeptik March 28, 2014 04:43

Turbulence convergence problems
 
I have had all described problems in my 2-blade rotor case.

It seems that the solution should be such as written below:

1. upwind schemes for K and Omega
2. low 1e-6 meanings for both variables at inlets and openings, at walls i've left it for a small value corellate to velocity of the wall. I used wallFunctions.

sivakumar March 28, 2014 05:21

Hi Ilya,
First of all your question is not clear, no body have time to read all the post from the beginning, so be specific about your problem, as well the thread you chosen is nearly 4 years old, the people involved in that discussion may have forgotten the solution to the problem, try to find the latest thread or else start new one.

there are few questions

--> are you using wall function? or resolving boundary layer?

if you are intending to use wall function, the value for k and omega should be estimated in standard way.

In the case of Low Re (resolving boundary layer), you should give k and Omega small value 1e8.

For turbulent quantities, first order upwind scheme is recommended.

if this answer didt help you, please post you problem clearly.

Thanks,
Sivakumar

skeptik March 28, 2014 05:56

Quote:

Originally Posted by sivakumar (Post 482602)
Hi Ilya,
First of all your question is not clear, no body have time to read all the post from the beginning, so be specific about your problem, as well the thread you chosen is nearly 4 years old, the people involved in that discussion may have forgotten the solution to the problem, try to find the latest thread or else start new one.

there are few questions

--> are you using wall function? or resolving boundary layer?

if you are intending to use wall function, the value for k and omega should be estimated in standard way.

In the case of Low Re (resolving boundary layer), you should give k and Omega small value 1e8.

For turbulent quantities, first order upwind scheme is recommended.

if this answer didt help you, please post you problem clearly.

Thanks,
Sivakumar

1. Of course people from this theme forgot their cases, but for newest ones google is working.
2. Yes, i'm using wall functions and all variables are calculated but it needs initial values anyway.
3. Despite to my suggestions problem stands still. OpenFOAM does not crash due to high k and omega but pressure field is not realistic.


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