A Pitot-Prandtl-Preston tube may be used to determine the shear stress at a wall in a turbulent boundary layer (Fig. E4.3). The tube is in contact with the wall and the shear stress is read from a calibration curve between the velocity head and the boundary shear stress. On the basis of the velocity distribution in the inner wall region, justify the Pitot-Prandtl-Preston tube's method.
