Helical Vortices in Swirling Flow

This study investigates the characteristics of the secondary motion in swirling flows induced by 180 degree twisted tapes in circular pipes. The characteristics of the flow are analyzed using Laser Doppler Velocimetry (LDV) measurements, flow visualizations and numerical simulations. Helical vortices are identified for the first time downstream of twisted tapes swirlers, explaining the apparent counter-rotating flow observed in previous studies of swirling flows. Helical vortices occur often in nature but the vortices described here are the first stable helical vortices ever observed. Their stability allowed detailed air bubble visualizations of the complex flow field resulting from the interaction between the helical vortices and the main swirl. Numerical simulations are used to explain the formation mechanism and the behavior of the helical vortices. The results are expected to contribute to improvements in mixing technologies and also help researchers understand complex vortex interactions.