The spanwise non-uniformity of nominally two-dimensional turbulent boundary layer : 2nd Report Wall shear stress and flow field

Abstract

In some cases the velocity distribution in a turbulent boundary layer shows remarkable spanwise non-uniformity even though the outer condition is is sufficiently two-dimensional from a practical point of view. In the previous paper, the authors described the characteristics of the spanwise non-uniformity in detail, from the experimental results of the spatial distributions of the streamwise velocity, turbulent intensity in the turbulent boundary layer and wall shear stress on two types of flat plates. In this report, the scale and mechanism of the streamwise vortices are investigated by the measurements of the flow direction in the turbulent boundary layer. A floating element type device is made 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 Clauser chart and the Preston tube method. From the result, 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.