Experimental invetigation of corotating vortex filaments in a water tunnel

The dynamic behavior of corotating vortex filaments is investigated in a water tunnel. Comparisons are made between the motion of a single filament and that resulting from interactions between two filaments. Correlation is observed visually between the merger location and the vortex strength. In most cases vortex merger is shown to occur within one orbit. Quantitative data are presented on the variations of the vortex span, the amplitude of motion, the spiraling rate, and the center of spiraling, all as functions of downstream distance. It is shown that the vortex span does not vary considerably except in cases where the interactions among the filaments are strong. The amplitude of motion is shown to be much larger than that of a single vortex, while growing with downstream distance. Furthermore, the amplitude of motion is shown to exhibit a preferred direction in some cases. The presented data reveal that in the two-vortex cases the spiraling rate is nearly constant. It is also shown that despite considerable motion of the filaments the center of spiraling does not deviate significantly from a straight line.