Vortex ring propagation and interactions studies

This paper experimentally investigates the vortex ring propagation and interactions with thin cylindrical and flat surfaces. Dye-based visualization technique is adopted for the interaction studies. Vortex rings are generated from a circular nozzle of 19 mm diameter with the stroke length ratios (length of the fluid slug to nozzle diameter, L_N/D_N) of 1 to 5, and ejection velocities in the range of 0.05 to 0.2 m/s. Vortex interaction studies are carried out with two different bodies; firstly, with the circular cylinders having the diameters of 0.2, 0.6, 1.5 and 2.5 mm, and secondly with a flat solid surface. Results indicate that the trails in the vortex ring start following at L_N/D_N = 4. The influence of the initial velocity is found to be insignificant on the vortex ring diameter, however, found to depend on stroke length ratio. Vortex-cylinder interaction studies indicated that vortex velocity decreases with increase in cylinder diameter after the interaction. Reconnections of vortex rings are observed in lower cylinder diameter cases. In case of vortex ring interaction with the flat surface, stretching of the vortex core is observed leading to a considerable increase in the vortex ring diameter.