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-   -   fvm::div(phi, Ug)...how to insert properly? (http://www.cfd-online.com/Forums/openfoam-solving/108207-fvm-div-phi-ug-how-insert-properly.html)

sawyer86 October 17, 2012 06:11

(U_j+Ug_j)*d(U_i+Ug_i)/dx_j...how to insert properly?
 
Hi there,

My question can be seen even from this prospective. I have to insert in the equation this term:

(U_j+Ug_j)*d(U_i+Ug_i)/dx_j

where Ug_i are the components of a given velocity field and U is the velocity I want to solve. This above is the convective term in the expression "u*grad(u)"-like

how can I do? Is it possible?

Thank you in advance!

treima October 17, 2012 06:23

Hi,

how did you initialise Ug, is it equal to the initialisation of U? Or perhaps there are some problems with the implicit and explicit treatment. You can have a look at this thread: http://www.cfd-online.com/Forums/ope...operation.html. There is a description of the same problem.


regards

treima

akidess October 17, 2012 06:24

You do not solve for Ug, hence that term is explicit. phi is not the variable you solve for, it's the data from the previous iteration.

sawyer86 October 17, 2012 06:32

(U_j+Ug_j)*d(U_i+Ug_i)/dx_j
 
Quote:

Originally Posted by akidess (Post 387043)
You do not solve for Ug, hence that term is explicit. phi is not the variable you solve for, it's the data from the previous iteration.

Hi,

one question. Do you say that the volume velocity flux is given from the previous iteration...that's so the way how icoFoam treats the non linear-convective term in the way to linearize it, am I right?

This linearization influence the calculation of UEqn.H()...but if I do insert that term explict how does UEqn.H() must change?

My question can be seen even from this prospective. I have to insert in the equation this term:

(U_j+Ug_j)*d(U_i+Ug_i)/dx_j

how can I do? Is it possible?

Thank you very much

sawyer86 October 17, 2012 06:36

Quote:

Originally Posted by akidess (Post 387043)
You do not solve for Ug, hence that term is explicit. phi is not the variable you solve for, it's the data from the previous iteration.

(U_j+Ug_j)*d(U_i+Ug_i)/dx_j

Sorry I did not explain this term. It is essentially the convective term when you do a kind of linearization starting from a base flow...like in the RANS, but different...

Then the term i exactly want to add is the part of the above expression:

U_j*dUg_i/dx_j

...?

sawyer86 October 17, 2012 06:45

Quote:

Originally Posted by treima (Post 387042)
Hi,

how did you initialise Ug, is it equal to the initialisation of U? Or perhaps there are some problems with the implicit and explicit treatment. You can have a look at this thread: http://www.cfd-online.com/Forums/ope...operation.html. There is a description of the same problem.


regards

treima

Thank you for the answer but i had a look of that thread and this is not just what I am looking for. By the way thank you again!

Regards


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