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Wall functions implementation for CFD turbulence models (k-e k-w) in COMSOL
Posted 02.06.2017, 15:30 GMT-4 Fluid & Heat, Computational Fluid Dynamics (CFD), Results & Visualization Version 5.2a 0 Replies
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I have 3 questions related to the implementation of the wall functions in the k-e and k-w CFD turbulence models.
1- As stated in the the CFD Module User's Guide and as seen in the equations in COMSOL, there's a no-penetration condition u*n=0 for the wall boundaries. But after looking at the results for various models (Cylinder pipe, 2D Backward Facing Step) I can see that u*n is not exactly 0 at walls boundaries. Even worse, for the 2D Backward Facing Step, near the step stagnation point, the flow go in and out of the wall boundaries. My first question is: how does COMSOL set the no-penetration condition for wall functions internally?
The 2 other questions are related to the implementation of the spf.d_w_plus and spf.delta_w.
2- Why is the minimum value of spf.d_w_plus at 11.06 (Intersection between the logarithmic and the linear law) when the log layer starts more near 30?
3-Also, setting the d_w_plus and varying the wall distance seems a bit odd to me since you are literally changing the distance from the mesh to the wall. Wouldn't it be better and give more accurate results if you set a uniform wall distance and be sure that the d_w_plus is most of the time in the log layer region (generally between 30 to 100-300)?
Thank you in advance!
Hello Jean-Philippe Simoneau
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