Evolution of swirling flow in a circular tube after a vane swirler at moderate Reynolds numbers
V.M. Molochnikov1,2, N.D. Pashkova1,2, A.A. Paereliy1
1FRC Kazan Scientific Center of RAS, Kazan, Russia
2Kazan National Research Technical University named after A.N. Tupolev (KAI), Kazan, Russia
Keywords: swirler, flow swirl, smooth channel, swirl degree, vortex core precession, laminar-turbulent transition, root-mean-square velocity pulsations, flow intermittency, velocity pulsation spectrum
Abstract
The experimental results on the swirling flow structure behind a vane swirler in a smooth tube at an axial flow Reynolds number varying within Re = 240 - 1640 are presented. A change in the degree of flow swirl along the tube length is analyzed as a function of the Reynolds number. The main patterns in the evolution of the profiles of longitudinal and circumferential velocity components and the distribution of the mean square pulsations of the longitudinal velocity component with increasing distance from the swirler are determined. It is shown that at Re = 1640, flow instability develops in the tube, which is a consequence of the formation of a reverse flow region on the tube axis in the immediate vicinity of the swirler. The influence of flow swirl on the appearance of signs of a local laminar-tur-bulent transition in vicinity of the tube axis and near its wall is analyzed (a sharp increase in the mean square velocity pulsations with increasing Reynolds number and the appearance of intermittency in the flow velocity oscillograms). It has been established that in the near-wall region, local turbulence of the flow is caused by the interaction between the swirler vane wakes and the wall.
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