Amlaan,

With K-Epsilon Realizable (in Fluent Ansys), we use “non-equilibrium wall functions” for most cases with high Reynolds number and for which it is quite expensive to resolve the viscous sublayer.

In fact try to make sure that the mesh either coarse or fine enough to avoid placing the wall-adjacent cells in the buffer layer (5 < y+ < 30).

if the characteristic Reynolds number is quite low or if near wall characteristics need to be resolved, it is better to use "enhanced wall treatment".

Best regards

Attached file gives some guidelines about Y+.

Thanks for your answers . I am simulating the flow of air from a 90 mm inlet dia 300 mm long compressor the flow goes through a domain which is also 300* 300 depth (2mm)

Inlet Pressure is 2 bar (Marked in screenshot)

Outlet Pressure 1 bar( atmospheric condn)

In my simulation I get Wall y+

Facet Max- 1020

Facet Min- 2.7

Avg WALL Y+ - 54

As I am using K epsilon realizable scalable wall function the value should be between 30-300

which I am not getting

I am using inflation layer (.053mm) first layer height 4 layers at a growth rate of 1.2

@Mr Mounir in which cases do we use non equilibrium wall functions ?

Hi Amlaan,

when dealing with wall functions in turbulence modeling, it is important to ensure a suitable number of computational nodes in the "laminar sublayer".

If an insufficient number of nodes is ensured, results may be misrepresented thus leading to inappropriate predictions.

I suggest you to put at least 5-10 nodes in the sublayer whose thickness can be approximately predicted by suitable correlations.

Don't hesitate to contact me if you need more.

Paolo