THE INFLUENCE OF SOLID BOUNDARIES UPON AERODYNAMIC SOUND
THE INFLUENCE OF SOLID BOUNDARIES UPON AERODYNAMIC SOUND
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DOI：
10.1098/rspa.1955.0191
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发表时间：
1955-01-01
影响因子：
--
通讯作者：
CURLE, N
中科院分区：
文献类型：
--
作者：
CURLE, N
对莱特希尔气动声的一般理论作了扩展，纳入了固体边界对声场的影响。这种影响是双重的，即(i)声波在固体边界处的反射和衍射，以及（ii）在固体边界处产生偶极子场，这是Lighthill四极子分布的极限。结果表明，这些效应完全等价于偶极子的分布，每一个偶极子代表单位面积的固体边界作用于流体的力。量纲分析表明，在大距离处偶极子产生的声强应为一般形式iocp0u600 - 3l2x -2，其中eu0为流体的典型速度，Lis为物体的典型长度，a0为静止流体中的声速，p0为静止流体的密度。因此，如果马赫数足够小，这些偶极子应该比莱特希尔理论中的四极子更有效地产生声音。结果表明，偶极声的基频是四极声频率的一半。
An extension is made to Lighthill’s general theory of aerodynamic sound, so as to incorporate the influence of solid boundaries upon the sound field. This influence is twofold, namely (i) reflexion and diffraction of the sound waves at the solid boundaries, and (ii) a resultant dipole field at the solid boundaries which are the limits of Lighthill’s quadrupole distribution. It is shown that these effects are exactly equivalent to a distribution of dipoles, each representing the force with which unit area of solid boundary acts upon the fluid. A dimensional analysis shows that the intensity of the sound generated by the dipoles should at large distancesxbe of the general form IocP0U60a0-3L2x-2, whereU0is a typical velocity of the flow,Lis a typical length of the body,a0is the velocity of sound in fluid at rest and P0is the density of the fluid at rest. Accordingly, these dipoles should be more efficient generators of sound than the quadrupoles of Lighthill’s theory if the Mach number is small enough. It is shown that the fundamental frequency of the dipole sound is one half of the frequency of the quadrupole sound.