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Old   December 2, 2013, 02:21
Default Problem with INTERPHASECHANGEFOAM
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Baris (Heewa)
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Dear Foam users,

i am studying modeling of cavitation inside of the nozzle. Therefore, i tried before cavitatingFoam solver and obtained not bad result. However, i couldnt obtained transient cavitation with it, therefore i switched to use interphaseChangefoam solver by using SchneerSauer model. I am using OF version 2.1.1 and when i set the initial U and p_rgh settings according to tutorial as follow;

0/U:
Code:
dimensions      [0 1 -1 0 0];
internalField   uniform (0 -3.5 0);
boundaryField
{
    inlet
    {
        type            fixedValue;
        value           $internalField;
    }
    outlet
    {
        type            pressureInletOutletVelocity;
        phi             phi;
        value           $internalField;
    }
    wall
    {
        type            fixedValue;
        value            uniform (0 0 0);
    }
0/Prgh:
Code:
Code:
dimensions      [1 -1 -2 0 0];
internalField   uniform 100000;
boundaryField
{
    inlet
    {
        type            zeroGradient;
    }
    outlet
    {
        type            fixedValue;
        value           $internalField;
    }
    wall
    {
        type           zeroGradient;
    }
In addition, for the scheme and solver i didnt change anything which means that they are same with tutorial. deltaT=10-8, However, when i checked the results; cavitation starts immediately (lets say from timestep between 0 to 100, and after 100, results shows everything vel, pres constant and i obtained alpha1 overprediction as seen at the attached figure. ) I am surprised that
why cavitation starts immediately?
why after 100 time step everything becomes constant?

I thought that maybe mesh number problem and i tried much finer mesh with the same initial conds. same result.

then i changed the conds as follow based on the inlet pressure acc. to experimental result; this time i couldnt obtain any cavitation and even sometimes alpha1 became negatif whereas with the same conditions i had really good results with cavitatingFoam.
0/U:
Code:
dimensions      [0 1 -1 0 0];
internalField   uniform (0 0 0);
boundaryField
{
    inlet
    {
         type            zeroGradient;
    }
    outlet
    {
        type            inletOutlet;
        inletValue       uniform (0 0 0);
    value         uniform (0 0 0);
    }
    wall
    {
        type            fixedValue;
        value            uniform (0 0 0);
    }
prgh:
Code:
InternalField   uniform 1e5;
boundaryField
{    inlet
    {
         type            fixedValue;
        value           uniform 2.22e5;     
    }
    outlet
    {
        type            fixedValue;
        value           uniform 1e5;     
    }
    wall
    {
        type           zeroGradient;
    }
Pls could you give some advices what kind of reasons let me have these strange results and how can i correct it?

as addition, i checked new version of interphasechangefoam (2.2.2) and i saw new treatment as alhpa2 and there are some differences in the codes of pEqn.H, alphaEqn.H, alphaEqnSuccycle.H,..

Please could someone tell me that which version of interphasechangefoam gives good result? Or is there anyone who got resonable result before with this solver?


Thnaks in advance
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File Type: jpg results.jpg (71.2 KB, 36 views)
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Old   December 2, 2013, 07:42
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Tobias Holzmann
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Hi shipmen,

I can not give you lot of advice to the solver because I only used it to build a new solver with temperature dependend phase change.

Additionally I never used cavitationFoam.


You should ask yourself if your Problem can be solved with RANS / URANS. The Picture of the measurement seems to be very unsteady. Maybe you have to calculate this with LES.

Additionally - what turbulence model do you use? Maybe your viscosity model fails in that case?


Did you compare the results of cavitationFoam and interPhaseChangeFoam?
Any differences in p, U, p_rgh, etc.?


Did you use the same turbulence model in both cases, same schemes, same boundary conditions?

At least (if its possible) you could extend your cavitationFoam (i think it is steady state) to transient solver. I am not so familiar with the Phase Change theory but you can test it and add the partial differential term of time to your equations.

PS: did you initialize your interPhaseChangeFoam with the steady-state solution?

Regards Tobi
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Old   March 26, 2014, 13:36
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vut
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Dear Tobi,

I am looking for initializing a LES from RANS solution.

For LES, I used pimpleFoam. It runs quite well the initial solutions in folder 0/ with the following files U, p, k, nuTilda and nuSgs.

However, RANS (RNG k-epsilon) gave me also good results. The lastest time folder (iteration no. 5000, for example) contains U, p, k, epsilon, nut and nuTilda.

May you give some advices to initialize pimpleFoam from the RANS solution?

Thanks you in advance,

vut
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