乱流境界層中における大規模渦の成長と崩壊 : 第2報, 過度の流れ方向変化

抄録

The present experiment investigates streamwise change of the vorticity field around a largescale coherent vortex artificially induced in a fully developed turbulent boundary layer. The vortical structure of the large-scale vortex evolved downstream through the growth, the self-preserving and the decay stages. In the growth stage, its spanwise and normal circulations increased downstream, and the large-scale vortex grew to have vortical structure similar to the natural horseshoe vortex. The vortex still grew upward but the spanwise circulation was kept nearly constant in the self-preserving stage. The convection velocity of its head and leg was 0.56 U_∝ in the growth and self-preserving stages. In the decay stage, each part of the vortex drifted at the local mean velocity, and the vortex became more inclined downstream. There, its vorticity gradually decreased as it flowed downstream. The decay rate of the normal vorticity was smaller than that of the spanwise one throughout the stages.