# fvm::div(phi, Ug)...how to insert properly?

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 October 17, 2012, 05:11 (U_j+Ug_j)*d(U_i+Ug_i)/dx_j...how to insert properly? #1 Member   Tom Join Date: Jan 2012 Location: France Posts: 43 Rep Power: 8 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! Last edited by sawyer86; October 17, 2012 at 13:08.

 October 17, 2012, 05:23 #2 Member   Join Date: Mar 2012 Location: Munich, Germany Posts: 67 Rep Power: 7 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

 October 17, 2012, 05:24 #3 Senior Member     Anton Kidess Join Date: May 2009 Location: Germany Posts: 1,274 Rep Power: 23 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. __________________ *On twitter @akidTwit *Spend as much time formulating your questions as you expect people to spend on their answer.

October 17, 2012, 05:32
(U_j+Ug_j)*d(U_i+Ug_i)/dx_j
#4
Member

Tom
Join Date: Jan 2012
Location: France
Posts: 43
Rep Power: 8
Quote:
 Originally Posted by akidess 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

October 17, 2012, 05:36
#5
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Tom
Join Date: Jan 2012
Location: France
Posts: 43
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Quote:
 Originally Posted by akidess 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

...?

Last edited by sawyer86; October 17, 2012 at 06:24.

October 17, 2012, 05:45
#6
Member

Tom
Join Date: Jan 2012
Location: France
Posts: 43
Rep Power: 8
Quote:
 Originally Posted by treima 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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