Takaishi T, Miyazawa M, Kato C
Railway Technical Research Institute, Shiga, 521-0013, Japan.
J Acoust Soc Am. 2007 Mar;121(3):1353-61. doi: 10.1121/1.2431345.
A numerical investigation is made of the production of sound by turbulence interacting with a noncompact body. The problem is formulated in the frequency domain by extending the theory of vortex sound proposed by Howe. The anomalous "numerical" generation of sound by the sudden termination of Lighthill's stress tensor at the outer boundary of a finite computational domain is avoided by identification of "scattered" sound sources that generate sound principally by interaction with the solid surface. It is argued that the boundary element method is the most efficient means of computing the aeroacoustic Green's function for the problem, because it requires a minimum of CPU time, is not prone to numerical errors such as dispersion and dissipation during propagation, and the radiation condition is easily applied at the outer boundary. The method is applied to the problem of sound generation by high Reynolds number flow past a circular cylinder. The "scattered" sources are shown to be confined to the vicinity of the cylinder surface. At low frequencies the radiation has a dipole-like directivity in agreement with the compact approximation. However, the directivity is quite different at high frequencies, where our noncompact method predicts a more complicated "leaf-like" radiation pattern.
对湍流与非紧致物体相互作用产生声音的问题进行了数值研究。通过扩展豪提出的涡旋声理论，在频域中对该问题进行了公式化表述。通过识别主要通过与固体表面相互作用产生声音的“散射”声源，避免了在有限计算域的外边界处因莱特希尔应力张量突然终止而导致的异常“数值”声产生。有人认为，边界元法是计算该问题气动声学格林函数的最有效方法，因为它所需的中央处理器时间最少，在传播过程中不易出现诸如色散和耗散等数值误差，并且辐射条件易于在外边界应用。该方法应用于高雷诺数流绕过圆柱体产生声音的问题。结果表明，“散射”声源局限于圆柱体表面附近。在低频时，辐射具有偶极子状的指向性，与紧致近似一致。然而，在高频时指向性有很大不同，在高频时我们的非紧致方法预测出一种更复杂的“叶状”辐射模式。
