in kepsilon wall function approach high Re turbulence models: question of velocity
Hej,
I looked through the different wall function for kepsilon turbulence models, however I feel I am missing something. In Wilcox (Turbulence modeling for CFD 2006) as well as many other publications, in wall functions the velocity seems to be set in the first grid point. In OpenFOAM, the following properties are changed with wall functions in the example of the kepsilon turbulence model,

took a while but here is a solution to the problem
Hej,
I think I found the solution to this. I found it in Pope, Turbulent Flow, 2000 under the way that wall functions are created. The original question was why the velocity is not set by any of the wall function. The answer is, that wall functions are apparently more robust by setting the shear stress and not the velocity, which makes sense when looking at separation points and other nasty flow phenomena, in which the velocity can become essentially 0. The way this is for the kepsilon model done is nutkWallFunction

Thanks roman
it was very helpful. 
hi
Whould you explain more and Why stage 4 is done? 
Quote:
The easiest way to introduce this source term into the equation is by modifying the turbulent viscosity, see Pope, Turbulent Flows, 2000, pp 442443 and Versteeg and Malalasekera, An introduction to computational fluid dynamics: The finite volume method, pp. 276277 
Quote:
Thank you for your explain. I have a question about the wall function for nonlinear models. As the nonlinear model can't be depicted by a simple turbulent viscosity, how can we set the shear stress? say we obtained the shear stress as in your form: u_shear * U_p,real / U_p,nominal, so we should set the Reynolds shear stress by u_shear * U_p,real / U_p,nominal  nu*dU/dy, here, y represents the wallnormal direction. However, the nonlinear Reynolds stress is not symmetric, it has 6 shear stress components, which one should be modified? I'm confused by this problem for some days. I'm looking forward for your reply. Thank you Xianbei 
All times are GMT 4. The time now is 11:34. 