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-   -   BubbleFoam alpha equation (https://www.cfd-online.com/Forums/openfoam-solving/60483-bubblefoam-alpha-equation.html)

 alberto June 23, 2005 05:48

Hello, I have a question on t

Hello,
I have a question on the implementation of the eulerian model in bubbleFoam.

Why the alpha equation has been implemented as:

fvScalarMatrix alphaEqn
(
fvm::ddt(alpha)
+ fvm::div(phi, alpha, scheme)
+ fvm::div(-fvc::flux(-phir, beta, scheme), alpha, scheme)
);

and not as

fvScalarMatrix alphaEqn
(
fvm::ddt(alpha)
+ fvm::div(phia, alpha, scheme)
);

Best regards,
Alberto

 henry June 23, 2005 05:51

To maintain boundedness of alp

To maintain boundedness of alpha at the 1 limit as well as the 0 limit.

 alberto June 23, 2005 07:27

Thank you Henry. Alberto

Thank you Henry.

Alberto

 sanglee August 24, 2005 02:55

Could anyone explain the deffe

Could anyone explain the defference between,
fvm::ddt(rho,e), and rho*fvm::ddt(e) ?

 henry August 24, 2005 03:16

Does rho vary with time?

Does rho vary with time?

 sanglee August 24, 2005 03:38

Yes, rho varies with time.

Yes, rho varies with time.

 henry August 24, 2005 03:46

In that case they are clearly

In that case they are clearly different, the first is the rate of change of rho*e and the second is rho* the rate of change of e, wasn't that obvious?

 sanglee August 24, 2005 04:13

Yes, it is obvious. Could you

Yes, it is obvious.
Could you tell me the correct expression among the following ones;

fvm::ddt(rho,e)=( (rho)^^(n+1)*e^^(n+1) - (rho)^^n*e^^n )/dt or
fvm::ddt(rho,e)=( (rho)^^n*e^^(n+1) - (rho)^^n*e^^n )/dt

Or, if both are not correct, give me correct one please .
Thank you

 henry August 24, 2005 04:20

The first expression correspon

The first expression corresponds to an Euler-implicit discretisation of fvm::ddt(rho,e) and the second is clearly equivalent to an Euler-implicit discretisation of rho*fvm::ddt(e).

If you need to know these details you should look at the source code, it is all there ready and waiting for you, all you have to do is load it into an editor. The files you need to look at for implicit temporal discretisation are all in OpenFOAM-1.2/src/OpenFOAM/finiteVolume/ddtSchemes.

 sanglee September 21, 2005 01:33

Dr. Weller I am trying to imp

Dr. Weller
I am trying to implement energy equation in bubbleFoam. I have problems with the disapprearing phases. As I reviewed your technical report, TR/HGW/02, Derivation...., I got an idea that your phase intensive momentum equation approach might help me. Could you give me some comments on using phase intensive energy equation instead of using the energy equation in conservative form.

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