reactingFoam, UEqn explained and diffusion calculation
 

Hello everyone,

I am using reactingFoam solver and am trying to fully understand the Ueqn file, which is a subject I have never found thoroughly explained:

"
fvm::ddt(rho, U)
+ fvm::div(phi, U)
+ turbulence->divDevRhoReff(U)
==
rho*g
+ fvOptions(rho, U)
"

First entry is for time variation, second for convection, and what about third and last entries, turbulence->divDevRhoReff(U), and fvOptions(rho, U), what is it doing exactly?

And how does it include diffusion when solving in laminar regime? It would be expected to see a laplacian term, I guess.

Any help is much appreciated!
Thanks in advance :)

Hi,


If you have a look at laminar solvers, you will indeed see a viscosity diffusion term in this equation.
For solvers which allow for turbulence, this diffusion term is in-cooperated in the turbulence->divDevRhoReff(U) term. What exactly that term does, depends on your turbulence model. One of the simplest turbulence models modifies your viscosity using the turbulent viscosity (see: http://www.cfd-online.com/Wiki/Bouss...ity_assumption), and hence you can see why the viscosity-term in in-cooperated with the turbulence model.

fvOptions(rho, U) is a rather new function, which allows users to add source terms to the equation without modifying the solver. A decent explanation is found here: http://www.openfoam.org/version2.2.0/fvOptions.php

Thanks Kevin!