Databases from numerical simulation of wall-bounded flows with closed reverse flow regions were examined in order to derive models, which relate the mean wall shear stress to flow quantities in a certain distance from the wall. The approach makes use of the particular shape of the profiles of turbulent shear stress which balances the streamwise pressure gradient outside the viscosity-affected near-wall region. One model version requires as input the streamwise pressure gradient and a velocity scale UW which results from linear extrapolation of the mean flow to the wall. Its application is restricted to the part of the reverse flow region with nonvanishing adverse pressure gradient. A more general applicable skin-friction law is derived from the observation that near-wall mean velocity profiles approximately collapse if they are scaled in a defect form. This scaling holds up to approximately half a bubble length downstream of attachment. Numerical values for model coefficients vary slightly from flow to flow and seem to depend on the Reynolds number.

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