壁面突起の形状がヘアピン渦の発達に与える影響

抄録

It was well known that the boundary layer has a preferred wavenumber of perturbation. Therefore, it may be possible to delay the transition to turbulence and reduce the turbulent frictional drag by artificially deforming the hairpin vortex to narrow the spacing in the flow direction and increase the wavenumber. The purpose of this study is to investigate the differences in the downstream development of the hairpin vortex when it is uniformly deformed in the width direction by obstacles placed on the wall surface. The results obtained show that the boundary layer was also unstable for obstacles with a height of about the displacement thickness of the boundary layer, and that they were effective in promoting transition to turbulent flow of the hairpin vortex, regardless of the cross-sectional shape of the obstacle. However, only for a triangular obstacle with a height 10 times the viscous length, the development of the hairpin vortex was slightly weakened. From these results, it was found that the height of the obstacle should be limited to less than 10 times the viscous length to deform only the hairpin vortex, and the gradient of the leading edge of the obstacle should be gentle to weaken the development.