CFD Online Discussion Forums - Bug in UEqn of twoPhaseEulerFoam?

CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)

- OpenFOAM Bugs (https://www.cfd-online.com/Forums/openfoam-bugs/)

- - Bug in UEqn of twoPhaseEulerFoam? (https://www.cfd-online.com/Forums/openfoam-bugs/86527-bug-ueqn-twophaseeulerfoam.html)

Bug in UEqn of twoPhaseEulerFoam?

Hi All:

I've spent some time interpreting the UEqn.C of twoPhaseEulerFoam. The momentum equation seems OK. however, the drag term seems problematic:

See the following link for the standard momentum equation.
http://openfoamwiki.net/index.php/BubbleFoam

In the UEqn.H, the momentum equation is :

Quote:

00022 UaEqn =
00023 (
00024 (scalar(1) + Cvm*rhob*beta/rhoa)*
00025 (
00026 fvm::ddt(Ua)
00027 + fvm::div(phia, Ua, "div(phia,Ua)")
00028 - fvm::Sp(fvc::div(phia), Ua)
00029 )
00030
00031 - fvm::laplacian(nuEffa, Ua)
00032 + fvc::div(Rca)
00033
00034 + fvm::div(phiRa, Ua, "div(phia,Ua)")
00035 - fvm::Sp(fvc::div(phiRa), Ua)
00036 + (fvc::grad(alpha)/(fvc::average(alpha) + scalar(0.001)) & Rca)
00037 ==
00038 // g // Buoyancy term transfered to p-equation
00039 - fvm::Sp(beta/rhoa*K, Ua) //Drag term
00040 //+ beta/rhoa*K*Ub // Explicit drag transfered to p-equation
00041 - beta/rhoa*(liftCoeff - Cvm*rhob*DDtUb)
00042 );
00043
00044 UaEqn.relax();
00045 }

The drag term should involve the difference between Ua and Ub, not just Ua.

I've tried to implement that (Ub-Ua), I just added the following line in the rhs:

+ fvm::Sp(beta/rhoa*K, Ub)
For the UbEqns, I've done a similar modification
Am I right? Anyone can help?

The explicit part of the drag that contains Ub has been transferred to pEqn.H. Have a look there and see if it makes sense to you.

Yes, Thanks for your reply, it really helps!

The effect of particle-particle interaction is also included if we set g0>0, However, note that there is g0 in radial Model (we get g0 and g0Prime), and we also define g0 in ppProperties.

Both alphaEqn.H and pEqn.H are using phi_pp, which involves g0, So which g0 are they using?

Thank you in advance.

Zhen

If you use the kinetic theory model, you should set g0 in ppProperties to zero.

Hi Alberto
I am reading the code of kineticTheory in twoPhaseEulerFoam. I find there are some annotation in kineticTheory.C such as "construct the granular temperature equation (Eq. 3.20, p. 44)" in line 61. So, can you tell me which book include these equation. Furthermore, where can I find the theory about g0 in ppProperties!

Quote:

Originally Posted by nygbook (Post 309267)

Berend van Wachem 's Ph.D. thesis.

Quote:

So, can you tell me which book include these equation. Furthermore, where can I find the theory about g0 in ppProperties!

In the literature ppMagf is identified as G(alpha) = d(pa)/d(alpha), being pa the particle pressure, and it is called "normal stress modulus". You find it in Gidaspow's early papers for example.

Best,

Does anyone know how to get the van Wachem Thesis? There's nothing online. Does anyone have a pdf?

Quote:

Originally Posted by grjmell (Post 321726)

Does anyone know how to get the van Wachem Thesis? There's nothing online. Does anyone have a pdf?

Not true! I needed 30sec using google twice (because I knew that he got his PhD at TU Delft) to find it

http://repository.tudelft.nl/view/ir...-83b1416709a6/

enjoy!
Florian

Oh dear! I was googling for ages but couldnt find it...!
Thanks for proving me wrong! :o