The effect of forced disturbances on vortex breakdown

A preliminary experimental investigation was conducted to study the effects of external forcing on the vortex in a vortex tube. The vortex tube had a slit entrance tangent to the tube's inner diameter and perpendicular to the tube's axis. Various dye flow visualization methods were used to visualize the vortex flow and the core. Forcing was introduced into the flow through axial periodic blowing, suction, or a combination of both. Forcing was also introduced through periodic tangential blowing. The vortex core developed helical waves with relatively long wavelengths when constant blowing was used. Periodic pulsation of the axial flow, at various low frequencies, resulted in various wavelength helical waves superimposed on the vortex core. High frequency forcing was found to result in a tighter core and therefore resulted in the delay of the vortex burst in the divergent segment of the tube. Suction along the core axis at the location of vortex burst was able to eliminate the burst. The burst did not re-form until the suction apparatus was pulled to a position approximately one vortex tube diameter (1.5 inches locally) downstream. Further investigations are planned since some of the observations reported here are significant.