Dual-Wavelike Instability in Vortex Rings

A series of experimental observation are presented a dual-wavelike instability in vortex rings. The first one is presented at Reynolds number range between 600 and 1000 for circular vortex ring and the second one could be observed in radiant-symmetric vortex rings, azimuthal number n ≥ 2, at least covers the Reynolds number from 275 to 1000. The azimuthal number of the first instability depends on the ratio η (of core radius to ring radius), while the azimuthal number of the second case accords with the shape of the orifice and the frequency of the second instability are also affected by the ratio η. The experimental results are compared with some theoretical prediction. Key–Words: vortex ring, dual-wavelike, instability, azimuthal number, Reynolds number