CFD Online Discussion Forums

CFD Online Discussion Forums (
-   Main CFD Forum (
-   -   question for specific dissipation rate (

kippo November 20, 2010 17:13

question for specific dissipation rate
Hi all,

a basic question: What is the mathematical correct definition of omega (specific dissipation rate in the k-omega)?

I cannot find a correct answer, anywhere. Also in Wilcox's book it is not mathematically described. Even in all books and publications I got, it is only derived by the turbulent viscosity definition.

Is it according to the Baldwin-Lomax as div x c ?

Hope, someone has a clue...



Hamidzoka November 21, 2010 04:16

Dear Kippo;
omega has a different meaning in k-omega turbulence models. it can be stated as:


in which epsilon is eddy dissipation, K is turbulence kinetic energy and C is the model constant. although in some versions of k-omega C is defined as a function of mean flow strain and rotation rates and omega itself implicitly.


kippo November 22, 2010 05:08

Thnx a lot,

but this is again all the time the same definition I get.
What I mean is the following: To derive the equation for k, you can take the trace of the Reynold-shear-stress tensor.
epsilon will occure in the equation in this way:


the k-equation is the trace of the Rij-tensor: Meaning in the k-equation, which can be derrived by avg(u'i*Ns(ui))=0
you will get a dissipation-term like the following (factor 2 is not there, because trace):


meaning, epsilon is a tensor built out of the second derivation of the turbulent energy k (correct?).
the units for k~m/s, epsilon~m/s

If you look then to the specific dissipation rate omega, as also defined as omega=epsilon/(C*k)~1/T (according to the turbulent viscosity definition),
then omega should be mathematically seen a tensor built by the tensors k/epsilon.

But what is then the correct mathematic definition.

If you look further to the k-omega-SST equations. Menter transformed the epsilon in the k-epsilon to suit the omega-equation. So an additional term occurs in the transformed epsilon-equation:


(this is the cross-diffusion modification, see manuals CFX of Fluent, or StarCD).

Where can I derive this term from the epsilon and omega-definition?

Or again, what is the correct mathematical definition of omega?

thnx a lot,


All times are GMT -4. The time now is 05:43.