Oscillations near wall for wall function grid
 

Dear all,
I am trying to solve a simple channel flow using buoyantSimpleFoam solver. my RAS model is compressible::BSL_EARSM similar to what is implemented in CFX. When I simulated the flow using (y+ ~ 1) mesh without the wall functions, everything was okay. The problem comes when I use wall function mesh (y+ ~ 35). When I look the results, I see large fluctuations in the Ux,Uy and Uz near the wall. After a few cells this fluctuations die down. I have observed similar fluctuations when using the kOmegaSST model but with very low magnitude. I am unable to find the reason for such high magnitudes. It would be really helpful if someone can help me out.

https://s11.postimg.org/l5osffff3/image.png

https://s11.postimg.org/ipmz1kxcf/Ux_line_Plot.png

https://s11.postimg.org/nct13ckpb/image.png

https://s11.postimg.org/v6tmoqsi7/Uy_line_Plot.png

https://s11.postimg.org/u5xzdd0wf/image.png

https://s11.postimg.org/lc72w9dxr/Uz_line_Plot.png



Thanks,

khedar

contd.
 

Here attached are the photos from kOmegaSST run.

https://s11.postimg.org/sw8sv431b/image.png

https://s11.postimg.org/obmmg6jbz/Ux_line_Plot.png

https://s11.postimg.org/45j4hanof/Uy_line_Plot.png

https://s11.postimg.org/bmsbwid7j/Uz_line_Plot.png


These are taken at the outlet of the channel.