Sound Generation in Oblique Collision of Two Vortex Rings

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A theory of vortex sound formulated in the forna of multipole expansions is applied to theoblique collision of two vortex rings at right angles. Using the theoretical f'orrnula for the far-fieldacoustic pressure excited by a tinae-dependent localized vorticity distribution, the coefficients of'the rnuJtipole modes of the wave pressure are estimated by the nutnerical data of cornputersinaulation. Time evoltrtion of the vorticity field is obtained by solving a viscous inconapressiblevorticity equation with a vorticity-potential method developed for a three-dinuensional vorticityfield in a bounded domain. Ntnmerical simulations are carried out for two kinds of vortex ringswith the same core paratneters but different ring radii, and the details of the vortex motion dvrringthe obliqtre collision are studied ntrrnerically. Conaputed znain-mode atnplitudes of the wavepresstrre excited by the vortex motion are found to be consistent with those of the experimentallyobserved acoustic wave not only qualitatively btut also quantitatively. From conuparison of' thequadrtnpole and octapole modes of the far-field acoustic pressttre between the coznptrtation andthe experinaent, it is possible to estimate the slenderness ratio of a core raditus to a ring radius of'the experirnental vortex ring. It is reraaarkable that the present simulation gives data identifyingthe source region for the wave emission. Strong acoustic source is identified at the location wherevorticity field varies very rapidly during vortexline reconnection,
社団法人日本物理学会の論文
1998-07-15

Sound Generation in Oblique Collision of Two Vortex Rings

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