Wall units.
 

When dealing with backward facing step problems, What are "wall units"? How do they relate the grid spacings?

Re: Wall units.
 

No such terms in general textbooks. You may consult specific references.

Re: Wall units.
 

Probably, when you measure the length of the inverse flow zone in units of height of the breakaway.

Re: Wall units.
 

I guess you are talking about Y+ values. If so, due to de-attachment, there is no meaningfull definition when dealing with steps. I would use same boundary layer mesh as for the incomming flow. For in-core flow I would define the mesh based on re-atachment length or mixing layer thickness (depending on flow behavior) Hope this helps