[Raza Javed]

Hello Everyone,


I have a question related to boundary conditions.


I have a pipe in my geometry. And I know the flow-rate of a fluid at the inlet. So, I am using flowRateInletVelocity boundary condition for velocity at the inlet. But I don't know which boundary condition to put for velocity at outlet?


Second, what type of boundary conditions are suitable for Pressure at inlet and outlet in this case?
I don't have any particular requirement for pressure in my simulation.


Any help is highly appreciated.


Thank you

[jherb]

For velocity put zeroGradient or inletOutlet at the outlet.


For pressure: zeroGradient at the inlet and fixedValue (or fixedMean) at the outlet.

[Raza Javed]

Thank you so much for your reply.


I am using chtMultiRegionSimpleFoam and my OpenFoam version is 4.1.



I have changed the boundary conditions as you suggested. But I am still getting an error.


My problem is that when I change the values of velocity and pressure, my solver RUNS but after some iterations, it gives an error that "maximum number of iterations exceeded". And then I tried to reduce the time interval in the "controlDict" file, then my solver runs completely without error, but my final residual is too high that it doesn't seem to be converging.



I am posting my solver log and my changeDictionaryDict (boundary conditions).
if you can please have a look, I shall be very thankful because I am not able to interpret the log because I am new to OpenFoam.


changeDictionaryDict File

boundary
{
    inlet
    {
        type            patch;
    }
    outlet
    {
        type            patch;
    }

}
U
{
    internalField   uniform (0 1e-3 0);

    boundaryField
    {
        inlet
        {
            type                fixedValue;//flowRateInletVelocity;//pressureInletVelocity;//
            //volumetricFlowRate  0.2;
            //extrapolateProfile  yes;
            value               uniform (0 1e-3 0);
        }

        outlet
        {
            type                inletOutlet;//zeroGradient;////
            value               $internalField;//uniform (0 0 0);//
            inletValue          $internalField;
        }
        "fluid_to_box"
        {
            type                noSlip;
        }
    }
}

T
{
    internalField   uniform 300;

    boundaryField
    {
        inlet
        {
            type            fixedValue;
            value           uniform 300;//$internalField;
            
        }

        outlet
        {
            type            inletOutlet;
            value           $internalField;
            inletValue      $internalField;
        }

        "fluid_to_box"
        {
            type            compressible::turbulentTemperatureCoupledBaffleMixed;
            Tnbr            T;
            kappaMethod     fluidThermo;
            value           uniform 300;
        }
    }
}


epsilon
{
    internalField   uniform 0.01;

    boundaryField
    {
        inlet
        {
            type            fixedValue;
            value           uniform 0.01;
        }

        outlet
        {
            type            inletOutlet;
            inletValue      uniform 0.01;
        }

        ".*"
        {
            type            epsilonWallFunction;
            value           uniform 0.01;
        }
    }
}

k
{
    internalField   uniform 0.1;

    boundaryField
    {
        inlet
        {
            type            inletOutlet;
            inletValue      uniform 0.1;
        }

        outlet
        {
            type            zeroGradient;
            value           uniform 0.1;
        }

        ".*"
        {
            type            kqRWallFunction;
            value           uniform 0.1;
        }
    }
}


p_rgh
{
    internalField   uniform 0;

    boundaryField
    {
        inlet
        {
            type            fixedFluxPressure;//zeroGradient;
            value           uniform 0;
        }

        outlet
        {
            type            fixedValue;
            value           uniform 0;
        }

        ".*"
        {
            type            fixedFluxPressure;
            value           uniform 0;
        }
    }
}
p
{
    internalField   uniform 0;

    boundaryField
    {
        inlet
        {
            type            zeroGradient;
            //value           uniform 1;
        }
        outlet  
        {
            type            fixedValue;
            value           uniform 0;
        }        
        "fluid_to_.*"
        {
            type            zeroGradient;
        }
    }
}

Log File

Time = 4


Solving for fluid region fluid
DILUPBiCG:  Solving for Ux, Initial residual = 0.6911749, Final residual = 0.04280814, No Iterations 2
DILUPBiCG:  Solving for Uy, Initial residual = 0.6577878, Final residual = 0.04376797, No Iterations 2
DILUPBiCG:  Solving for Uz, Initial residual = 0.5181872, Final residual = 0.02078987, No Iterations 2
DILUPBiCG:  Solving for h, Initial residual = 0.5998981, Final residual = 0.03528898, No Iterations 2


--> FOAM FATAL ERROR: 
Maximum number of iterations exceeded

    From function Foam::scalar Foam::species::thermo<Thermo, Type>::T(Foam::scalar, Foam::scalar, Foam::scalar, Foam::scalar (Foam::species::thermo<Thermo, Type>::*)(Foam::scalar, Foam::scalar) const, Foam::scalar (Foam::species::thermo<Thermo, Type>::*)(Foam::scalar, Foam::scalar) const, Foam::scalar (Foam::species::thermo<Thermo, Type>::*)(Foam::scalar) const) const [with Thermo = Foam::hConstThermo<Foam::rhoConst<Foam::specie> >; Type = Foam::sensibleEnthalpy; Foam::scalar = double; Foam::species::thermo<Thermo, Type> = Foam::species::thermo<Foam::hConstThermo<Foam::rhoConst<Foam::specie> >, Foam::sensibleEnthalpy>]
    in file /home/ubuntu/OpenFOAM/OpenFOAM-4.1/src/thermophysicalModels/specie/lnInclude/thermoI.H at line 66.

FOAM aborting

#0  Foam::error::printStack(Foam::Ostream&) at ??:?
#1  Foam::error::abort() at ??:?
#2  Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::constTransport<Foam::species::thermo<Foam::hConstThermo<Foam::rhoConst<Foam::specie> >, Foam::sensibleEnthalpy> > > >::calculate() at ??:?
#3  Foam::heRhoThermo<Foam::rhoThermo, Foam::pureMixture<Foam::constTransport<Foam::species::thermo<Foam::hConstThermo<Foam::rhoConst<Foam::specie> >, Foam::sensibleEnthalpy> > > >::correct() at ??:?
#4  ? at ??:?
#5  __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
#6  ? at ??:?
Aborted (core dumped)

[mrishi]

Hi,
Can you share log a little prior to Time=4? The final residuals for each variable seem to have a very high value and yet only 2 iterations are made to solve it.
It might also help to look at the fvSolution dictionary where these controls are defined.

[Raza Javed]

Thank you so much for your reply.


I try to explain my problem from the start.


I am attaching my geometry with this. one image is the complete box and the other one is inside box.(3 blue long rectangles and one green pipe with inlet and outlet).


I made this geometry on Salome, and then I imported in Openfoam using UNV file.


Then I put my boundary conditions using system/region_name/changeDictionaryDict.


My requirement is that I need to put some fix velocity at the inlet and there is a temperature change along the fluid region due to some hot plates working as heat sources outside the walls of fluid region. And then, I want to see the temperature change at the outlet of the fluid region. I don't have any particular requirement for pressure in my simulation. With these conditions, I want to check at which value of velocity does my simulation reaches the steady state? Also I defined my fluid to be laminar flow. Is it correct?



My problem is that when I change the values of velocity and pressure, my solver RUNS but after some iterations, it gives an error that "maximum number of iterations exceeded". And then I tried to reduce the time interval in the "controlDict" file, then my solver runs completely without error, but my final residual is too high that it doesn't seem to be converging.



And I have one question here is that, is it possible to model laminar flow in this type of pipe? because with the same boundary conditions, I have a small geometry as well and that is working without errors.


Thank you

[mwaqas]

Hella Raza,


Please also attach your log file, fvSolution and controlDict to have better understanding about the problem.


Regards