[beauty]

Hi, friends
I encountered some problems about the drag models in the twoPhaseEulerFoam solver.
1）First one is about the calculation of particle Remolds number in drag models. For example, in sourcefile of WeYu.C, the code is as follows:

Foam::tmp<Foam::volScalarField> Foam::WenYu::K
(
const volScalarField& Ur
) const
{
volScalarField beta = max(scalar(1) - alpha_, scalar(1.0e-6));
volScalarField bp = pow(beta, -2.65);

volScalarField Re = max(Ur*phasea_.d()/phaseb_.nu(), scalar(1.0e-3));
volScalarField Cds = 24.0*(scalar(1) + 0.15*pow(Re, 0.687))/Re;

forAll(Re, celli)
{
if(Re[celli] > 1000.0)
{
Cds[celli] = 0.44;
}
}

return 0.75*Cds*phaseb_.rho()*Ur*bp/phasea_.d();
}
From the code, the particle Remolds number is calculated by Re=ρb|Ur|da/μb, and the Ur is defined via const volScalarField& Ur. But in theory, Remolds number is defined as Re=ρbUrda/μb. I am a rookie with C++, is the sentence const volScalarField& Ur equals to|Ur|?
2）Second is the compile error when change the blue line to:
volScalarField Cds = 24.0*(scalar(1) + 0.15*pow(Re*beta, 0.687))/(Re*beta);
I attach my source file and the log of wmake.
Look forward to your advance.
Thanks!

beauty

[l_r_mcglashan]

1) You have to send it the magnitude of the relative velocity. You can see this within the twoPhaseEulerFoam solver in liftDragCoeffs.H.

2) I'm not sure. Did you 'wmake libso' in interfacialModels?

[beauty]

Hi
Thank you for your help. Yes, it is like you said I have to send the magnitude of the relative velocity, which is executed by liftDragCoeffs.H in twoPhaseEulerFoam. Miss the file (liftDragCoeffs.H) is my fault.
I didn’t “wmake libso” in interfacialModels. I just performed “wmake” in terminal. Is this the problem?

beauty

[l_r_mcglashan]

I assume that what you did was copy one of the dragModels and alter it slightly? You need to recreate the library libEulerianInterfacialModels. You'll see in the folder twoPhaseEulerFoam/interfacialModels there is a folder Make/ add your new model to Make/files, and then run 'wmake libso' from the folder twoPhaseEulerFoam/interfacialModel. You'll then be able to use your new drag model.

[beauty]

Originally Posted by l_r_mcglashan

I assume that what you did was copy one of the dragModels and alter it slightly? You need to recreate the library libEulerianInterfacialModels. You'll see in the folder twoPhaseEulerFoam/interfacialModels there is a folder Make/ add your new model to Make/files, and then run 'wmake libso' from the folder twoPhaseEulerFoam/interfacialModel. You'll then be able to use your new drag model.

yes, you are right. I just copy one dragModel and alter it. Then I add my new model to Make/files, and run wmake.Today I compiled the dragmodel following your guidance, everything is ok. Thank you very much.
beauty

[mksingh]

Originally Posted by beauty

yes, you are right. I just copy one dragModel and alter it. Then I add my new model to Make/files, and run wmake.Today I compiled the dragmodel following your guidance, everything is ok. Thank you very much.
beauty

================================================== =======
Hi
Regarding twoPhaseEulerFoam in OF1.6, I tried a simple 3-D bubble column, but never successful in getting right results. Some times I get very unstable free surface and after a certain point I see that whole domain is filled with continuous phase. Have you encountered the same problems with TwoPhaseEulerFoam?
With regards.
M K

[alberto]

Originally Posted by beauty

volScalarField Cds = 24.0*(scalar(1) + 0.15*pow(Re*beta, 0.687))/(Re*beta);

Why do you divide by beta?

I know it is "common practise" to see that around, but Wen & Yu drag does not contain alpha inside the Reynolds number. The correction due to the presence of more than one particles is made introducing the beta^{-2.65}, the rest stays the same as in the single-particle case.

[alberto]

Originally Posted by mksingh

================================================== =======
Hi
Regarding twoPhaseEulerFoam in OF1.6, I tried a simple 3-D bubble column, but never successful in getting right results. Some times I get very unstable free surface and after a certain point I see that whole domain is filled with continuous phase. Have you encountered the same problems with TwoPhaseEulerFoam?
With regards.
M K

Usually this happens because your Courant number (time step) is too big.

Best,

[beauty]

Originally Posted by mksingh

================================================== =======
Hi
Regarding twoPhaseEulerFoam in OF1.6, I tried a simple 3-D bubble column, but never successful in getting right results. Some times I get very unstable free surface and after a certain point I see that whole domain is filled with continuous phase. Have you encountered the same problems with TwoPhaseEulerFoam?
With regards.
M K

Hi
I didn't encounter the same problem. I am a rookie to openfoam, so I can't give you good solution, I feel so sorry. Maybe the reason is as Alberto said, your time step is too big. I have seen a paper about simulaiton of the gas-solid fluidized bed, in which the time step is set to 0.00001.
beauty

[beauty]

Hi, Alberto
After seeing your reply, I check my equation again. The WenYu drag Model I have read in paper is different from the expression in openfoam. I can't write formula here, so I attached a file. what is your opinion?
beauty

[alberto]

Hello,

they're both used. I checked again, and you find both of them reported as "Wen & Yu (1966)" model. I'll try to find the original paper from Wen & Yu (1966) to clarify.

[alberto]

Originally Posted by beauty

I have seen a paper about simulaiton of the gas-solid fluidized bed, in which the time step is set to 0.00001.

Quite normal time step for dense fluidized beds. Usually 5 10^-4 - 10^-5, and even smaller if you introduce frictional models.

Best,

[beauty]

Originally Posted by alberto

Hello,

they're both used. I checked again, and you find both of them reported as "Wen & Yu (1966)" model. I'll try to find the original paper from Wen & Yu (1966) to clarify.

Hi
It's happy to see that. I also have the idea to find the original paper. Please let me know what's the result.

beauty

[alberto]

I didn't have time to go to the library and dig it out. In the meanwhile, the good review of

Enwald, Peirano and Amstedt, "Eulerian two-phase theory applied to fluidization", Int. J. Multiphase Flow, 1996

report that Wen & Yu used the Schiller and Naumann correlation for Cd, which does not contain alpha multiplying the Reynolds number.

Best,