A numerical study on helical vortices induced by a short twisted tape in a circular pipe

Helical vortices, as one kind of secondary flows, are recently observed downstream of the short twisted tape. The behaviors of vortices, which have significant effects on the efficiency of twisted tape, are not well understood. As such, the formation and development of helical vortices induced by the short twisted tape are studied numerically. The results show that two symmetrical stable helical vortices are present downstream of the twisted tape. The values of radial velocities cannot be neglected due to the presence of the vortices. The vortices form in the twisted tape and remain the structure downstream of the twisted tape. Torsion promotes the formation of helical vortices. The intensities of helical vortices decay along the streamwise direction. With the increasing Reynolds numbers, the intensities of helical vortices increase, and the trend is in agreement with the swirl intensities. The intensities of helical vortices decay slowly compared with the intensities of swirling flow.