The spanwise non-uniformity of nominally two-dimensional turbulent boundary layer. II - Wall shear stress and flow field

The scale and mechanism of streamwise vortices are investigated by measuring the flow direction in a turbulent boundary layer. A floating element-type device is constructed, and the local wall shear stress is measured by this apparatus. The values of wall shear stress obtained by this method are compared with the values obtained by other methods, such as the Clauser chart and the Preston-tube method. It is inferred that the mean value of wall shear stress can be expressed by a two-dimensional equation even though the spatial variations of the mean velocity are remarkably large as in this case. The mechanism of the spatial variation of this turbulent boundary layer is clarified by using these experimental results.