Sound generation from the evolution and interaction of elliptic vortex
rings is calculated numerically. An elliptic vortex ring emits a stro
ng sound signal due to significant distortion and stretching of the vo
rtex filament. At the far field, the acoustic pressure is linearly dep
endent on the third time derivatives of the vortex positions. Therefor
e, a numerical scheme of high resolution is employed to describe in de
tail the elliptic vortex ring motions, which are highly non-linear. Di
scretized vortex filaments are interpolated by using a parametric blen
ding function to remove a possible numerical instability. The distorte
d vortex filament, owing to the self-induced velocity and the induced
velocity from the other vortex segments, is redistributed at each time
step. The accuracy and efficiency of the scheme are validated by comp
arisons with the analytic solution of circular vortex ring interaction
. Acoustic signals from the evolution of a single elliptic vortex ring
are obtained with various aspect ratios of the axes. Vortex motions a
nd acoustic signals from two identical elliptic vortex rings, placed i
nitially with selected separation distances, are calculated. Distinct
periods are obtained from the evolution of each single elliptic vortex
ring and the pairing process of two elliptic vortex rings. The calcul
ated periods in the acoustic signals depend to a significant degree on
the initial aspect ratio of the ring and the separation distance. (C)
1997 Academic Press Limited.