A new approach for estimation of the skin friction in turbulent boundary layer under the adverse pressure gradient conditions

Clauser-chart is commonly regarded as the only indirect method capable for estimation of the local mean skin friction in a turbulent boundary layer based on velocity profile in the overlapping layer, where the logarithmic relation is observed. This approach suffers, however, from the following limitation: it is applicable only for zero and weak pressure gradient flows. However, as is known, in a number of practical configurations the flow has a non-canonical character and is affected, in particular, by the adverse pressure gradient-here airfoils, diffusers and turbines may serve as examples. Hence, with this paper we would like to present a new method which can yield an accurate estimation of wall shear-stress under the strong pressure gradient conditions. In this approach the skin friction can be directly estimated based on the location of intersection point between the inner-scaled streamwise velocity profile and the newly found logarithmic line in the location which covers with the point of the local maximum of large scale motion activity in the outer region of the turbulent boundary layer. It was verified that the proposed method allows for estimation of the skin friction velocity with uncertainty lower than 2.5% for the Clauser-Rota pressure parameter beta up to 28 and for 1800 < Re-tau < 3900 using data from available literature.