Learning Forum

[hchingw]

I'm using ANSYS Fluent for some simulations in my dissertation. I wanted to ask about the energy equation used when running LES with incompressible fluid, no mixing or reaction. I found the energy equation listed in the ANSYS Fluent Theory Guide (in 5.2.1 Heat Transfer Theory) but I can't find the details about the turbulent thermal conductivity (k_t). Can anyone please link me to it if I missed it?

Is there a filtered form of the energy equation for LES in ANSYS Fluent? A link to that would be much appreciated.

[aitor.amatriain]

In ANSYS Fluent, the filter is the grid, so the equations are the same in RANS and LES. The difference lies in the calculation of mu_t.
As far as I am concerned, the value of k_t in LES is not explicitly written in the Theory Guide. However, I guess that it is k_t = mu_t*c_p/Pr_t.

[DrAmine]

Nice!

[hchingw]

Thank you for the answer! How is the turbulent Prandtl number Pr_t calculated and how is it related to the effective Prandtl number?

[aitor.amatriain]

Turbulent Prandtl number is a constant whose value is 0.85 by default. I have not read any definition of an "effective Prandtl number", although based on the definition of k_eff, I suppose that the effective Prandtl number is equal to (k+k_t)*c_p/(mu+mu_t)