Effect of foreign bodies on aerodynamic sound
作者:
V. R. Lauvstad,
期刊:
The Journal of the Acoustical Society of America
(AIP Available online 1974)
卷期:
Volume 56,
issue 5
页码: 1407-1417
ISSN:0001-4966
年代: 1974
DOI:10.1121/1.1903458
出版商: Acoustical Society of America
数据来源: AIP
摘要:
The paper deals with the problem of estimating the sound field generated by a limited region of turbulence containing foreign bodies of arbitrary shape and arbitrary composition. According to the Lighthill‐Curle acoustic analogy, the aerodynamically‐generated sound is the same as that due to a distribution of quadrupole and dipole sources within the fluid and over the surfaces of the bodies. It is known that the presence of foreign bodies will usually convert some of the intense nearfield energy of Lighthill's quadrupoles into the form of sound attributal to dipole and monopole sound whose amplitude is much greater than that of the free‐flow noise. Current trends towards more sophisticated theories have again focused attention on this problem with drastically different results. Calculations are here presented to determine the extent whereby this multipole‐conversion process actually is taking place. It is shown that a method involving matching of inner and outer expansions yields intensity laws of different orders of magnitude comparing favourably with observed results. Curle and Powell's attempts to solve the problem have been reexamined to show inconsistencies their analysis. In particular, Curle's retarded‐wave solutions are recasted by use of Fourier synthesis. It is suggested that much of the discrepancies between the results in the present paper and the predictions of Curle's theory can be explained by a more carefully conducted analysis, throwing emphasis on various possibilities by which pseudosound tuned to the presence of foreign bodies may give way to sound fields being many orders of magnitude stronger than those emerging from Curle's analysis.
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