To simulate transitional skin friction or heat transfer the conditionally a
verged Navier-Stokes equations are used. To describe the diffusion of frees
tream turbulence into the turbulence weighting factor tau is used. A transp
ort equation is presented for this tau -factor boundary layer and the inter
mittent laminar-turbulent flow behavior during transition, a including conv
ection, diffusion, production, and sink terms. In combination with the cond
itioned Navier-Stokes equations, this leads to an accurate calculation of f
low characteristics within the transitional layer. The method is validated
on transitional skin friction and heat transfer measurements, respectively
on a flat plate and in linear turbine cascade.