Laminar-turbulent transition in a smooth channel with local swirling of flow

A weakly swirling flow behind a vane swirler in a smooth pipe was investigated experimentally at the Reynolds numbers of the axial flow Re = 240 – 1640. The swirl ratio variation along the pipe depending on the Reynolds number was analyzed. The following signs of local laminar-turbulent transition were observed in the vicinity of the pipe axis and near the pipe wall: steep rise in the root-mean-square fluctuations of velocity with the increase in the Reynolds number and intermittency occurring in oscillograms of velocity. The mechanism of local turbulization of flow near the wall of the pipe was described.