rhoPimpleFoam with AMI crashed

anuargimenez · August 12, 2022, 15:54

Hi all,

I am trying to simulate a polymer flow through a single screw extruder, such as the one shown below:

I modified some libraries to correctly introduce the non-Newtonian fluid behavior and ran some steady simulations with the MRF approach and rhoSimpleFoam. Everything worked fine, they converge very well and have physical meaning.

Then I tried the AMI approach with rhoPimpleFoam and after a few iterations, the simulation crashed:

Code:

[1] #0  Foam::error::printStack(Foam::Ostream&)[3] #0  Foam::error::printStack(Foam::Ostream&)[4] #0  Foam::error::printStack(Foam::Ostream&)[5] #0  Foam::error::printStack(Foam::Ostream&)[2] #0  Foam::error::printStack(Foam::Ostream&)[0] #0  Foam::error::printStack(Foam::Ostream&) at ??:?
 at ??:?
[1] #1  [3] #1  Foam::sigFpe::sigHandler(int)Foam::sigFpe::sigHandler(int) at ??:?
[4] #1  Foam::sigFpe::sigHandler(int) at ??:?
[5] #1  Foam::sigFpe::sigHandler(int) at ??:?
[2] #1  Foam::sigFpe::sigHandler(int) at ??:?
[0] #1  Foam::sigFpe::sigHandler(int) at ??:?
[1] #2   at ??:?
[3] #2  ?? at ??:?
[4] #2  ? at ??:?
[5] #2  ? at ??:?
[2] #2  ? at ??:?
[0] #2  ? in "/lib/x86_64-linux-gnu/libc.so.6"
[4] #3  ? in "/lib/x86_64-linux-gnu/libc.so.6"
[5] #3  ? in "/lib/x86_64-linux-gnu/libc.so.6"
[1] #3  ? in "/lib/x86_64-linux-gnu/libc.so.6"
[3] #3  ? in "/lib/x86_64-linux-gnu/libc.so.6"
[2] #3  ? in "/lib/x86_64-linux-gnu/libc.so.6"
[0] #3  ? in "/lib/x86_64-linux-gnu/libm.so.6"
[5] #4  exp in "/lib/x86_64-linux-gnu/libm.so.6"
[4] #4  exp in "/lib/x86_64-linux-gnu/libm.so.6"
[1] #4  exp in "/lib/x86_64-linux-gnu/libm.so.6"
[2] #4  exp in "/lib/x86_64-linux-gnu/libm.so.6"
[3] #4  exp in "/lib/x86_64-linux-gnu/libm.so.6"
[0] #4  exp in "/lib/x86_64-linux-gnu/libm.so.6"
 in "/lib/x86_64-linux-gnu/libm.[5] #5so.6"
  Foam::rhoPolymerEOS<Foam::specie>::rho(double, double) const[4] #5  Foam::rhoPolymerEOS<Foam::specie>::rho(double, double) const in "/lib/x86_64-linux-gnu/libm.so.6"
 in "/lib/x86_64-linux-gnu/libm.so.6"
[1] #5  Foam::rhoPolymerEOS<Foam::specie>::rho(double, double) const[2] #5  Foam::rhoPolymerEOS<Foam::specie>::rho(double, double) const in "/lib/x86_64-linux-gnu/libm.so.6"
[3] #5  Foam::rhoPolymerEOS<Foam::specie>::rho(double, double) const in "/lib/x86_64-linux-gnu/libm.so.6"
[0] #5  Foam::rhoPolymerEOS<Foam::specie>::rho(double, double) const at ??:?
 at ??:?
 at ??:?
[1] #6  [2] #6  Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::polymerKWLFTransport<Foam::species::thermo<Foam::hPolymerThermo<Foam::rhoPolymerEOS<Foam::specie> >, Foam::sensibleEnthalpy> > > >::calculate()Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::polymerKWLFTransport<Foam::species::thermo<Foam::hPolymerThermo<Foam::rhoPolymerEOS<Foam::specie> >, Foam::sensibleEnthalpy> > > >::calculate()[3] #6  Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::polymerKWLFTransport<Foam::species::thermo<Foam::hPolymerThermo<Foam::rhoPolymerEOS<Foam::specie> >, Foam::sensibleEnthalpy> > > >::calculate() at ??:?
 at ??:?
[5] #6  Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::polymerKWLFTransport<Foam::species::thermo<Foam::hPolymerThermo<Foam::rhoPolymerEOS<Foam::specie> >, Foam::sensibleEnthalpy> > > >::calculate()[4] #6  Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::polymerKWLFTransport<Foam::species::thermo<Foam::hPolymerThermo<Foam::rhoPolymerEOS<Foam::specie> >, Foam::sensibleEnthalpy> > > >::calculate() at ??:?
[0] #6  Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::polymerKWLFTransport<Foam::species::thermo<Foam::hPolymerThermo<Foam::rhoPolymerEOS<Foam::specie> >, Foam::sensibleEnthalpy> > > >::calculate() at ??:?
 at ??:?
 at ??:?
 at ??:?
 at ??:?
[5] #7  [4] #[2] #7  [1] #7  7  [3] #7  Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::polymerKWLFTransport<Foam::species::thermo<Foam::hPolymerThermo<Foam::rhoPolymerEOS<Foam::specie> >, Foam::sensibleEnthalpy> > > >::correct()Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::polymerKWLFTransport<Foam::species::thermo<Foam::hPolymerThermo<Foam::rhoPolymerEOS<Foam::specie> >, Foam::sensibleEnthalpy> > > >::correct()Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::polymerKWLFTransport<Foam::species::thermo<Foam::hPolymerThermo<Foam::rhoPolymerEOS<Foam::specie> >, Foam::sensibleEnthalpy> > > >::correct()Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::polymerKWLFTransport<Foam::species::thermo<Foam::hPolymerThermo<Foam::rhoPolymerEOS<Foam::specie> >, Foam::sensibleEnthalpy> > > >::correct()Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::polymerKWLFTransport<Foam::species::thermo<Foam::hPolymerThermo<Foam::rhoPolymerEOS<Foam::specie> >, Foam::sensibleEnthalpy> > > >::correct() at ??:?
[0] #7  Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::polymerKWLFTransport<Foam::species::thermo<Foam::hPolymerThermo<Foam::rhoPolymerEOS<Foam::specie> >, Foam::sensibleEnthalpy> > > >::correct() at ??:?
[4] #8   at ??:?
[1] #8   at ??:?
 at ??:?
[5] #8  [2] #8   at ??:?
[3] #8   at ??:?
[0] #8  ?????? in "/opt/openfoam7/platforms/linux6 in "/opt/openf4GccDPInt32Opt/bin/rhoPimpleFoam"
 in "/opt/openoam7/platforms/linux64GccDPInt32O in "/opt/ofoam7/platforms/lipt/bin/rhoPimpleFoam"
nux64GccDPInt32O[5] #9  __libc_start_mainpenfoam7/platforms/linupt/bin/rhoPimplx64GccDPInt32Opt/beFoam"
in/rhoPimpleFo[1] #9  am"
[4] #__libc_start_main9  __libc_start_main[2] # in "/opt/openfo9  __libc_start_mainam7/platforms/linux64GccDPInt32Opt/bin/rhoPimpleFoam"
[3] #9  __libc_start_main in "/opt/openfoam7/platforms/linux64GccDPInt32Opt/bin/rhoPimpleFoam"
[0] #9  __libc_start_main in "/lib/x86_64-linux-gnu/li in "/lib/x86_64-linux-gnu/libc.so.6bc.so.6"
"
[4] #10  [3] #10   in "/lib/x86_64-linux-gnu/libc.so.6"
[2] #10   in "/lib/x86_64-linux-gnu/libc.so.6"
 in "/lib/x86_64-linux[5] #10  -gnu/libc.so.6"
[1] #10   in "/lib/x86_64-linux-gnu/libc.so.6"

I had never used AMI before, so I relied on https://holzmann-cfd.com/ tutorials from the brilliant @Tobi

This is the running log file:
runningLog.txt

Here you can see the continuity and residuals plot:
continuity.png
linear.png

My initial conditions are:

p:

Code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2112                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [1 -1 -2 0 0 0 0];

internalField   uniform 1e5;

boundaryField
{    
       
    inlet
    {
        type            zeroGradient;  
    }
    
    outlet
    {
        type            fixedValue;
        value           uniform 1e5;
    }
    
    barrelup
    {
        type            zeroGradient;
    }
      
    barreldown
    {
        type            zeroGradient;
    }
    
    screwup
    {
        type            zeroGradient;
    }

    screwdown
    {
        type            zeroGradient;
    }
    
    "AMI1|AMI2"
    {
        type            cyclicAMI;
    }
}


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

U:

Code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2112                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volVectorField;
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform (0 0 0);

boundaryField
{  
    
    inlet
    {
        type                flowRateInletVelocity;
        massFlowRate        6.1e-06;// kg/s  aprox. 0.36 kg/h
        rho                 rho;
        rhoInlet	     1040;  
    }
    
    outlet
    {
        type            zeroGradient;
        value           uniform (0 0 0);
    }
    
    barrelup
    {
	type            slip;
    }
      
    barreldown
    {
	type            noSlip;
    }
    
    screwup
    {
        type            movingWallVelocity;
        value           uniform (0 0 0);
    }
    
    screwdown
    {
        type            movingWallVelocity;
        value           uniform (0 0 0);
    }
    
    "AMI1|AMI2"
    {
        type            cyclicAMI;
    }
    
}


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

T:

Code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2112                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      T;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 0 0 1 0 0 0];

internalField   uniform 500; //initial condition

boundaryField
{   
    
    inlet
    {
        type            fixedValue;
        value           uniform 298.15; // temperature ambient 25ºC 
    }
    
    outlet
    {
        type            zeroGradient;
    }
   
   //ZONE 1: CONDUCTIVITY + RADIATION 
   barrelup
    {
	type            	convectiveRadiativeHeatFlux;
	mode            	convectiveRadiative;
	Ta              	constant 592.15;
	h               	uniform 215;			//Heat transfer coefficient    [W/(m²*K)]
	emissivityNozzle	0.95;				//Emissivity nozzle (or brass) [-]
	emissivityFilament	0.95;				//Emissivity filament [-]
	dNozzle		4.0;				//inner diameter nozzle [mm}
	dFilament		1.75;				//filament diameter [mm]
        kappaMethod     	fluidThermo;
        value           	$internalField;		//initial Temperature value
    }
     
    //ZONE 2: constant temperature.
    barreldown
    {
        type            fixedValue;
        value           uniform 590;
    }
    
    screwup
    {
        type            zeroGradient;
    }    
    
    screwdown
    {
        type            zeroGradient;
    }
   
    "AMI1|AMI2"
    {
        type            cyclicAMI;
    }

}


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

controlDict, fvSchemes and fvSolution are shown below:

Code:

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  7  
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application     rhoPimpleFoam;

startFrom       latestTime;

startTime       0;

stopAt          endTime;

endTime         6;

deltaT          1e-4;

writeControl    adjustableRunTime;

writeInterval   0.005;

purgeWrite      0;

writeFormat     binary;

writePrecision  6;

writeCompression off;

timeFormat      general;

timePrecision   6;

runTimeModifiable true;

adjustTimeStep  yes;

maxCo           20;

maxDeltaT	0.0025;


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

Code:

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  7
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    p
    {
       solver          GAMG;
        tolerance       1e-10;
        relTol          0.01;
        smoother        GaussSeidel;
        cacheAgglomeration no;
    }
    
    pFinal
    {
        $p;
        tolerance       1e-6;
        relTol          0;
    }

    "pcorr.*"
    {
        $p;
        tolerance       1e-3;
        relTol          0;
    }
    
    rho
    {
        solver          PCG;
        preconditioner  DIC;
        tolerance       1e-8;
        relTol          0.1;
    }

    rhoFinal
    {
        $rho;
        tolerance       1e-5;
        relTol          0;
    }

    "(U|h)"
    {
        solver          smoothSolver;
        smoother        symGaussSeidel;
        tolerance       1e-10;
        relTol          0.1;
    }

    "(U|h)Final"
    {
        $U;
        tolerance       1e-10;
        relTol          0;
    }
}


PIMPLE
{
    //- Correct the fluxes based on mesh motion. See header files of the solver
    correctPhi          true;

    //- Turn on of off the momentum predictor. In a numerical point of view
    //  not necessary. Useful for 2-phase and high viscosity ratios
    momentumPredictor   true;

    //- Use the SIMPLE(C) := C =  consistent / corrected algorithm for
    //  the outer corrections. A pressure term that is neglected in the
    //  SIMPLE algorithm is included. More inner calculations but the
    //  coupling U-p in general is solved faster
    consistent          true;

    //- Mesh non-orthogonality correctors. Foam handles non-orthogonality quite
    //  good, so there is no need to use or only up to 2 - 3
    nNonOrthogonalCorrectors 0;

    //- Outer loops, re-calculation around p-U and other equations within
    //  one time step. For stiff problems while using under-relaxation
    nOuterCorrectors    5;

    //- Pressure corrections
    nCorrectors         2;

    //- If the transient solution tends towards a steady state solution,
    //  end the calculation after the residual control is reached
    residualControl
    {
        p   1e-5;
        U   4e-6;
        h   1e-4;
    }

    //- Control over each time step. The outer loops are recalculated
    //  till the residuals are reached. For outer loops, we can use
    //  under-relaxation as it is kind of a SIMPLE loop. Stiff problems
    //  can be handled and the time step can be increased. Further information
    //  are given in the book Mathematics, Numerics, Derivations and OpenFOAM
    outerCorrectorResidualControl
    {
        //- Weak control - bad accuracy but faster
        p
        {
            relTol      0;
            tolerance   1e-3;
        }

        U
        {
            relTol      0;
            tolerance   1e-3;
        }
        
        h
        {
            relTol      0;
            tolerance   1e-3;
        }
    }
}

//- Relaxation factors applied to the fields or equations in the outer loops
//  If nOuterCorrectors is not used, no underrelaxation should be placed.
//  Always use the *.Final factor too, only you really know what your are doing
//  ++ Relaxation of the final outer correction is possible, if the residual
//     controls are very strict.
relaxationFactors
{
    //- Relaxation of the fields: See doxygen
    //  Range [0-1] while 0 does not change the field (no sense)
    fields
    {
        p               0.95;
        pFinal          1;
    }
    //- Relaxation of the equation:
    //  Factor: -1 disables the usage
    //  Factor: 1 makes the matrix diagonal dominant or at least equal
    //          --> matrix might be manipulated
    //  Factor: 0 < alpha < 1; underrelaxation - make matrix diagonal dominat
    //  Factor: alpha > 1; over-relaxation - make matrix diagonal dominat weak
    //          --> can be used in some cases, generally not stable
    equations
    {
        p       1;      // Make matrix at least diagonal dominant
        U       1;
        h       0.9;
    }
}


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

Code:

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  7
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default             Euler;
}

gradSchemes
{
    default         Gauss linear;
}

divSchemes
{
    default         Gauss upwind;
    div(phi,U)      Gauss linearUpwind grad(U);
    div(phi,h)      Gauss linearUpwind grad(h);
    div(((rho*nuEff)*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}

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

I already ran the checkMesh utility and the mesh seemed to be fine.
It would be a great help if you could give me some advice to manage this.

Thanks,
Anuar

anuargimenez · August 13, 2022, 04:25

Anyone who might be interested in the case?

spenceme · August 13, 2022, 05:58

I cannot confirm your overall setup and boundary files are 100% correct, but assuming you have run successfully with an MRF simulation maybe they are.

I would start with lowering the starting time step (perhaps to 1e-5), increase the outer correctors on your pimple loop from 5 to larger (perhaps 20), and decrease your target courant number to a smaller value, 20 is probably too large to get stability at least until the flow has initiated and stabilized. I would try with 1 for some timesteps and slowly increase to see where it diverges.

You ideally should be looking that the solution converges to your residual controls before it advances to the next time steps. Pushing to Co of 20 this early before having any more converged iterations is probably not going to be stable.

anuargimenez · August 13, 2022, 09:29

Hi spenceme, thank you very much for your reply.

I followed the instructions that you suggested and the solver crashes in the first timestep

It seems that the residuals in each iteration dont converge, dont know why it could be.

This is the running log:
runningLog2.txt

Thank you for your time,
Anuar

spenceme · August 13, 2022, 09:54

I would try some relaxation on u and p and more on h.

anuargimenez · August 13, 2022, 11:42

Thank you for your suggestions! Unfortunately, despite I tried different values for relaxation, the simulation keeps crashing.

I tried this configuration, as it is used in many rhoPimpleFoam tutorials:

PIMPLE
{
correctPhi yes;
nOuterCorrectors 2;
nCorrectors 1;
nNonOrthogonalCorrectors 0;

pRefCell 0;
pRefValue 0;
}

relaxationFactors
{
equations
{
".*" 1;
}
}

It keeps running, however the initial residual of pressure always remains 1. This is the residuals plot now:
Imagen1.png

Here you can see the last timeStep:

Code:

Courant Number mean: 5.77082e-06 max: 9.93088e-05
deltaT = 4.01532e-08
Time = 3.16779e-05

AMI: Creating addressing and weights between 50424 source faces and 50424 target faces
AMI: Patch source sum(weights) min/max/average = 0.998807, 1, 0.999998
AMI: Patch target sum(weights) min/max/average = 0.998811, 1, 0.999998
GAMG:  Solving for pcorr, Initial residual = 1, Final residual = 0.000809554, No Iterations 50
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
smoothSolver:  Solving for Ux, Initial residual = 1.21937e-05, Final residual = 9.73018e-11, No Iterations 189
smoothSolver:  Solving for Uy, Initial residual = 2.37258e-07, Final residual = 9.59816e-11, No Iterations 104
smoothSolver:  Solving for Uz, Initial residual = 1.72491e-05, Final residual = 9.92642e-11, No Iterations 199
- selecting all cells
- selected 11197318 cell(s) with volume 6.83952e-06
- selecting all cells
- selected 11197318 cell(s) with volume 6.83952e-06
smoothSolver:  Solving for h, Initial residual = 0.000362698, Final residual = 7.93305e-12, No Iterations 1
- selecting all cells
- selected 11197318 cell(s) with volume 6.83952e-06
GAMG:  Solving for p, Initial residual = 1, Final residual = 0.00973657, No Iterations 15
pressureControl: p max 9.41894e+08
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 4.75605e-10, global = 2.18067e-12, cumulative = 1.08047e-09
GAMG:  Solving for p, Initial residual = 1, Final residual = 0.00973657, No Iterations 15
pressureControl: p max 9.41894e+08
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 4.75605e-10, global = 2.18067e-12, cumulative = 1.08265e-09
GAMG:  Solving for p, Initial residual = 1, Final residual = 7.5759e-07, No Iterations 49
pressureControl: p max 9.59615e+08
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 3.70065e-14, global = 8.61469e-17, cumulative = 1.08265e-09
ExecutionTime = 4564.31 s  ClockTime = 4566 s

Any idea? I can't think of what else to try.
greetings,
Anuar

spenceme · August 14, 2022, 03:23

It looks like somewhere in your domain the pressure values are exploding. I would write the results and look where this is occurring. Perhaps something in your mesh at that location.

for BC, you might want to use pressureInletOutletVelocity instead of zero gradient on the U outlet.

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mixerVesselAMI2D's mass is not balancing	sharonyue	OpenFOAM Running, Solving & CFD	6	June 10, 2013 09:34

August 13, 2022, 04:25		#2
anuargimenez New Member Anuar Giménez Join Date: Feb 2022 Location: Spain Posts: 15 Rep Power: 4	Anyone who might be interested in the case?

August 13, 2022, 05:58		#3
spenceme New Member Max Spencer Join Date: Dec 2019 Posts: 11 Rep Power: 6	I cannot confirm your overall setup and boundary files are 100% correct, but assuming you have run successfully with an MRF simulation maybe they are. I would start with lowering the starting time step (perhaps to 1e-5), increase the outer correctors on your pimple loop from 5 to larger (perhaps 20), and decrease your target courant number to a smaller value, 20 is probably too large to get stability at least until the flow has initiated and stabilized. I would try with 1 for some timesteps and slowly increase to see where it diverges. You ideally should be looking that the solution converges to your residual controls before it advances to the next time steps. Pushing to Co of 20 this early before having any more converged iterations is probably not going to be stable. hogsonik likes this.

August 13, 2022, 09:29		#4
anuargimenez New Member Anuar Giménez Join Date: Feb 2022 Location: Spain Posts: 15 Rep Power: 4	Hi spenceme, thank you very much for your reply. I followed the instructions that you suggested and the solver crashes in the first timestep It seems that the residuals in each iteration dont converge, dont know why it could be. This is the running log: runningLog2.txt Thank you for your time, Anuar

August 13, 2022, 09:54		#5
spenceme New Member Max Spencer Join Date: Dec 2019 Posts: 11 Rep Power: 6	I would try some relaxation on u and p and more on h.

August 14, 2022, 03:23		#7
spenceme New Member Max Spencer Join Date: Dec 2019 Posts: 11 Rep Power: 6	It looks like somewhere in your domain the pressure values are exploding. I would write the results and look where this is occurring. Perhaps something in your mesh at that location. for BC, you might want to use pressureInletOutletVelocity instead of zero gradient on the U outlet. hogsonik likes this.