Partial slip boundary condition?

Baicang

Hi,

The vorticity at the edge of the near-wall region is defined,w=du/dy since dv/dx=0 at the wall. w*=Cf*U^2/vt where, w*=the dimensional wall vorticity;

U=maximum velocity in the outer flow region;

Cf=friction factor.

(1)I don't know how to understand the outer flow region,how it should be defined? (2)How to obtain the value of friction factor?

Thanks in advance.

Baicang