The spanwise non-uniformity of nominally two-dimensional turbulent boundary layer : 3rd Report, Influence of the streamwise vortices arising from the protrusion

In this report, results of an experimental investigation which was performed to eliminate the streamwise vortices arising in a nominally two-dimensional turbulent boundary layer of which behaviour was examined in detail in the authors previous paper, are presented. Though there may be two procedures of obliteration of streamwise vortices, the present work is concerned with the method to place the vortex generators like roughness element at the leading edge of a flat plate inducing the counter rotating vortices against pre-existing vortices in the boundary layer. Using this set, the authors measured the downstream development and uniformalization of the spatial variations of the boundary layer characteristics. From these results, it was revealed that the streamwise vortices were extremely stable, and large vortex generators must be used to eliminate these vortices. In addition, these streamwise vortices, which disappeared once in the course of the boundary layer development, exhibited a tendency to appear again in the downstream region. And a weak variation of velocity with large wave length at the outside of the layer produced by the protuberances was observed.