Laplacian term in NS equation
Hi All,
I have a little question on the NavierStokes implementation in OF. In the interPhaseChangeFoam solver the NS equation has written as: fvVectorMatrix UEqn ( fvm::ddt(rho, U) + fvm::div(rhoPhi, U)  fvm::Sp(fvc::ddt(rho) + fvc::div(rhoPhi), U)  fvm::laplacian(muEff, U)  (fvc::grad(U) & fvc::grad(muEff)) ); My question is: what does the term " (fvc::grad(U) & fvc::grad(muEff))" mean? In the theory that term shouldn't exist. if it's true the relationship laplacian(muEff, U)=muEff*laplacian(U)+grad(U)*grad(muEff) (see P38 in Programmers Guide) I make some mistake? Diego 
Quote:
Mirko 
Hi Mirko
I'm not sure of that. Why this terms should be zero when the solution is reached? Both therms are not zero at the end, and why the inner product should be zero? Could you send me a reference about that? Thanks a lot for the replay Diego 
Hi Diego,
The answer is here "http://www.cfdonline.com/Forums/openfoam/82640interfoamueqn.html" and here "http://powerlab.fsb.hr/ped/kturbo/OpenFOAM/SummerSchool2009/presentations/MitjaMorgut2009.pdf" 
Hi Pablo
I'm agree that if the muEff is not constant the terms "div(muEff*grad(U))" and "muEff*lapalcian(U)" are different, but in the Navie Stokes equation the first term is the right one. But as the OF Programmers Guide tell at P38, the openfoam command laplacian(muEff,U), should be intended as the div(muEff*grad(U)) and not asmuEff*lapalcian(U), so should be not necessary split the terms in two contribute in the equation. If I say something wrong...could you say me where? Diego 
Let me known if with this pic it is clearhttp://imageshack.us/photo/myimages/3/formulasns.jpg/
http://imageshack.us/photo/myimages/3/formulasns.jpg 
Pablo, you have errors in the bracketing of the equations in the three lines of your eqnarray. The final result is correct though :)

Thank you very much Pablo,
I found the little mistake in the brackets, but now all it is more clear. In every books i found that this therm is always hides in the source terms without explicit its. Thank you again. 
Sorry, brackets are wrong at the stress term.
Pablo 
transpose term
Dear All
I like to ask a question: What happen to the term of transpose of (Grad (U))? To what term it is converted in equation given in "http://imageshack.us/photo/myimages/3/formulasns.jpg/" Regards Ehsan 
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