A Method for Estimating Wall Friction in Turbulent Boundary Layers

We describe a simple method for estimating wall friction which uses the fit of velocity data to the boundary layer profile in wall units all the way from the wall to the end of the log region. Two different models for the boundary layer profile are examined, the power-series interpolation scheme of Spalding and the Musker profile which is based on the eddy viscosity concept. The accuracy of the new method is quantified using the zero pressure gradient 2-D turbulent boundary layer data of Österlund for which independent measurement of wall shear is available. Results show that the new procedure can provide accurate estimates of wall shear with a mean error of about two percent or better. The usefulness of this method is in its ability to provide accurate estimates of wall shear not only based on full velocity profile data but also sparse data points in the velocity profile, including only a single data point.