[tzaht]

Hi all,


I am trying to simulate a chamber with an outlet, and a mouth inside the chamber. The problem I am having is that I am trying to obtain a steady solution with the SIMPLE method, but my solution is not converging even after 20,000 iterations. Further, the velocity, k and Epsilon field are all kind 'splotchy'. I should further add, that the epsilon field reaches values of ~100, which are higher than the boundary condition I set on it of 0.025.



Setup

In the following three images, the outlet is the solid blue ring.










There are zero-gradient interfaces with the atmosphere, depicted in white.




Lastly, the mouth is the following 'disc'.








U Field:







Epsilon Field:

[tzaht]

My epsilon, k and U files are as follows:

Epsilon

dimensions      [0 2 -3 0 0 0 0];


internalField   uniform 0.025;

boundaryField
{
    walls
    {
        type            epsilonWallFunction;
        Cmu             0.09;
        kappa           0.41;
        E               9.8;
        value           uniform 0.125;
    }

    inlet
    {
        type            zeroGradient;
    }

    mouth
    {
//      type            zeroGradient;

        type            fixedValue;
        value           $internalField;
    }

    outlet
    {
        type            inletOutlet;
        inletValue      uniform 0.025;
        value           uniform 0.375;
    }

}

k

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


internalField   uniform 0.00375;

boundaryField
{
    walls
    {
        type            kqRWallFunction;
        value           uniform 0.375;
    }

    inlet
    {
        type            zeroGradient;
    }

    mouth
    {
        type            zeroGradient;
    }

    outlet
    {
        type            zeroGradient;
    }

}

U

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


internalField   uniform (0 0 0);

boundaryField
{
    walls
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }

    outlet
    {
        type        flowRateOutletVelocity;
        volumetricFlowRate    0.04; // 50/3600        // Volumetric/mass flow rate [m3/s or kg/s]
        value       uniform (0 0 0); // placeholder
    }

    mouth
    {
        type        flowRateInletVelocity;
        volumetricFlowRate    0.002; // 50/3600        // Volumetric/mass flow rate [m3/s or kg/s]
        value       uniform (0 0 0); // placeholder
    }

    inlet
    {
        type        zeroGradient;
    }

}

 }

p

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


internalField   uniform 0;

boundaryField
{
    walls
    {
        type            zeroGradient;
//      value           0;
    }

    outlet
    {
        type            zeroGradient;
//        value                 0;
    }

    inlet
    {
        type            fixedValue;
        value           uniform      0;
    }

    mouth
    {
        type            zeroGradient;
//        value                 0;
    }

Any advice on the following questions would be appreciated:


a) Whether it is normal to see such a high epsilon value given that it lies outside the boundary value and the remaining boundaries are zero value?


If a) is not normal, any insight to what I might be doing wrong.


Kind regards.

[tzaht]

Hi all,


I have a further update, and have tried to pose this question as briefly as possible.


I essentially have a chamber, in which there is an outlet whereby I fix the outflow. I also have an inflow from within the domain, where I have annotated 'mouth'. As there is a balance between total mass flux, I have left the 'inlet' as zeroGradient, and so flow should be coming from the outside environment into the chamber to balance the mass (incompressible flow).


In this particular image, I have no turbulence model, but no matter what turbulence model I have, I get these numerical blow-ups occurring near the outlet. I have tried all the various gradient schemes I have seen posted on cfd-online.



Any advice appreciated, as I am struggling to understand what is going wrong and have run out of ideas.