Acoustic emissions by vortex motions
Acoustic emissions by vortex motions
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DOI：
10.1017/s0022112086001301
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发表时间：
1986-12
影响因子：
3.7
通讯作者：
T. Kambe
中科院分区：
文献类型：
--
作者：
T. Kambe
通过总结我们最近的工作，讨论了涡旋运动声发射的基本问题。文中给出了三个典型的算例：(I)两个涡环迎头相撞，(Ii)一个涡环在圆柱体附近运动，(Iii)一个涡环在半无限大板的锐边附近运动。无粘流体低马赫数运动的气动声学理论预测，对于(I)-(III)，远场声压的幅值分别与U4、U3和U2.5成正比，其中U是单个涡环的平移速度。因此，在低马赫数时，涡缘相互作用在三种情况下产生的声音最大。我们的观察证实了这些比例定律。除了标度性质外，我们还给出了发射的波形以及方向性图案。迎头碰撞辐射的是四极方向性波，而偶极子波是由涡柱相互作用产生的。第三，涡旋-边缘相互作用产生心形方向性模式的波。这三种情况的波形都与虚势流的体积通量(通过涡环)的时间导数有关，这是每种构型的特征，尽管每种情况的时间导数的阶数不同。除了第一种情况的最后一个周期外，观测到的轮廓与理论预测的曲线吻合得出奇地好，在第一种情况下，粘性被认为起着重要的作用。观测到的波形如透视图所示。
Fundamental aspects of the acoustic emission by vortex motions are considered by summarizing our recent work. Three typical cases are presented as illustrative examples: (i) head-on collision of two vortex rings, (ii) a vortex ring moving near a circular cylinder, and (iii) a vortex ring moving near a sharp edge of a semi-infinite plate. The theory of aerodynamic sound for low-Mach-number motion of an inviscid fluid predicts that the amplitude of the acoustic pressure in the far field is proportional to U4, U3 and U2.5 for (i)-(iii) respectively, where U is the translation velocity of a single vortex ring. Therefore the vortex-edge interaction generates the most powerful sound among the three cases at low Mach numbers. Our observations have confirmed these scaling laws. In addition to the scaling properties, we show the wave profiles of the emission as well as the directionality pattern. The head-on collision radiates waves of quadrupole directionality, whereas waves of dipole property are originated by the vortex-cylinder interaction. The third, vortex-edge, interaction generates waves of a cardioid directionality pattern. The wave profiles of all three cases are related to the time derivatives of the volume flux (through the vortex ring) of an imaginary potential flow which is characteristic of each configuration, although the orders of the time derivatives are different for each case. The observed profiles are surprisingly well fitted to the curves predicted by the theory, except the final period of the first case, in which viscosity is assumed to play an important role. The observed wave profiles are shown in a perspective diagram.