ヘアピン渦列が先導する管内流の乱流遷移について

抄録

We examined pipe flow transitions to a turbulent puff, which is a local turbulence containing relaminarizing front and hardly fluctuating rear parts, against adding perturbation in a constant mass flux facility. Probability curve of the puff creation with respect to the intensity of perturbation displayed multiple thresholds for the transition at Reynolds number, Re = 1,900. Simple dye visualization confirmed that there is formation of hair-pin vortex array against the injecting small jet as the perturbations. Velocity field measurement by PIV elucidated that the transition does not depend on the intensity of hair-pin vortices represented by the circulation, but depends on place of the vortices. The vortices staying at the central region of the pipe keeps deformation of the base flow profiles and induces gradual transition in the downstream positions