[MatzeS]

Hello,

checking the term turbulence->divDevReff(U) I came up with the following question:

The diffusion term for incompressible flows should look somehow like this (here, I ignored the viscosity):

fvc::div(fvc::grad(U)+fvc::grad(U)().T())

And this can be transformed to this:

fvc::laplacian(U)

But when I implement that into OpenFOAM, those terms give different results. I assume it is connected to the discretization schemes, but even when I use linear for all schemes, it gives me different results.
So, what do I do wrong? What do I miss? Is it because of wall-functions or boundary conditions?
Any comment is appreciated...

Regards,
Matze

[jherb]

I think this wiki page might explain what is going on here:
http://openfoamwiki.net/index.php/Bu...DevReff.28U.29

Also have a look at this thread (the difference between compressible and incompressible models goes away if the continuity equation is fulfilled after convergence of the solution):
http://www.cfd-online.com/Forums/ope...ivdevreff.html

[Bernhard]

Originally Posted by MatzeS

Hello,

checking the term turbulence->divDevReff(U) I came up with the following question:

The diffusion term for incompressible flows should look somehow like this (here, I ignored the viscosity):

fvc::div(fvc::grad(U)+fvc::grad(U)().T())

And this can be transformed to this:

fvc::laplacian(U)

But when I implement that into OpenFOAM, those terms give different results. I assume it is connected to the discretization schemes, but even when I use linear for all schemes, it gives me different results.
So, what do I do wrong? What do I miss? Is it because of wall-functions or boundary conditions?
Any comment is appreciated...

Regards,
Matze

You ignored viscosity in your derivation. The turbulent viscosity is not constant, so you can't pull it through the differential.

[MatzeS]

Hello,

thank you for your reply, it was very helpful!

Regards,
Matze