code_saturne User's Forum

 
Previously César Vecchio wrote (https://code-saturne.info/products/code-saturne/forums/general-usage/335742424/931852726):
Now since here some comments have been made about the Hydraulic
Diameter, what about for external flows or 2D simulations? Or for inlets
that are not pipes in internal flows such as HVAC situations? Usually
for the latter I set up the hydraulic diameter as that of the inlet
which is for example the opening of a split air conditioner, so I'm
thinking now that the initial intants might not be accurate (as the runs
I did were long the effects must have dissipated after reaching steady
state).
Would it be logical setting the hydraulic diameter as, for example,
that of the frontal area of a wing or any other body in external flows?

 
For internal flows, at the inlet we use formulas which are in the functions keendb and keenin (file turent.f90).
For external flow, may be you can use:
k = 1.0e-6 * U**2
e = 4.5e-7 * U**3 / L
with U a reference velocity and L the length of the airfoil chord.
 
These values are taken from this article:
Spalart, P. R. and Rumsey, C. L.,
"Effective Inflow Conditions for Turbulence Models in Aerodynamic Calculations,"
AIAA Journal, Vol. 45, No. 10, 2007, pp. 2544-2553


 
Other suggestions or experiences are welcome.

Thanks for the info. So far I'm not really a friend of file routines, I have no idea of Fortran, but I see those routines in particular are easy to understand. I will try to make a simple Octave script to find an equivalent hydraulic diameter so I can have a fair initialization using the GUI. Only two doubts:
What are the "xkappa" and "cmu" values and where do you estimate them (maybe I know them under another name, piping was not my favorite part of Fluid Mechanics)?
Is this routine used by all the other turbulence models too? Usually I run laminar, but when I use turbulence I go for SST.
Thank you.
 
EDIT:
I found it, both answers:
First doubt (not my favorite source, but well...): http://en.wikipedia.org/wiki/Turbulence_kinetic_energy
Second doubt:  http://support.esi-cfd.com/esi-users/turb_parameters/
Thanks again! :)