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

cheng1988sjtu March 24, 2011 14:21

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?

l_r_mcglashan March 24, 2011 14:31

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.

cheng1988sjtu March 24, 2011 15:18

Thank 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

alberto March 25, 2011 02:19

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

nygbook May 25, 2011 21:21

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!

alberto May 25, 2011 23:11

Quote:

Originally Posted by nygbook (Post 309267)
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.

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,

grjmell August 26, 2011 06:11

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

florian_krause August 26, 2011 06:41

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

grjmell August 26, 2011 06:45

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


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