円管内乱流パフの生成過程におけるヘアピン渦列攪乱の影響

抄録

Visualizations of transition process triggered by disturbance injection in pipe flows were conducted. In order to investigate the influence of hairpin vortices formed by interaction between the mainstream and the injected jet on the transition process, the hairpin vortices and the secondary turbulence including turbulent puffs are distinguished from each other by the fluorescent dye and flake-like particles. Timeline images on the visualizations indicated different creation processes of a puff depending on the conditions, the disturbance amplitude A and disturbance injection time L*. In addition to this, a device generating microbubbles in the pipe by electrolysis of water was installed upstream the jet injection point, and the influence of generating microbubbles on the transition process was visualized. The results indicate that the microbubbles modify radial position of the hairpin vortex street and this modification enhances the transition.