Wall functions vs. boundary layers
 

Hello,

I am a bit confused about wall functions and meshes with layers on walls.

If I understand correctly, wall functions model boundary layer of the flow near the wall so it applies to first layer of cells in mesh. Those cells must be thicker than y+.

If I make a mesh with layers on walls thinner than y+ there is no need for wall functions because conditions in boundary layer are calculated directly.

Suppose I have a mesh from the latter case. What boundary conditions should I set for k and omega? What's the 'omega' value on the wall? Infinity?

How do I estimate y+ in a pipe?
The calculator (https://www.cfd-online.com/Tools/yplus.php) requires boundary layer length. What length should I use, say, for a very long pipe?

Thanks!

> What boundary conditions should I set for k and omega?

There is no need to set any wall functions in your case. Simply set a no-slip boundary condition at the walls.

I can't do that. I can set a noSlip BC for velocity but there's no such thing for k and omega. There is an omega BC called 'slip' but that's definitely not 'noSlip' :)

A few more questions.

When calculating y+, I need boundary layer length. What does that even mean? I have fully developed flow at the inlet, so what length should I choose?
I'm trying to simulate a centrifugal pump.