Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Korea.
Sci Rep. 2017 May 18;7(1):2125. doi: 10.1038/s41598-017-02143-y.
During the last decade, most of acoustic cloak research has been done within a theoretical framework in which the medium is at rest. However, such an acoustic cloak cannot preserve its unique properties or functions to make an object acoustically invisible in the presence of flow. In this study, we propose a theoretical framework to accurately investigate the effect of compressibility and non-uniformity in flow on the scattering pattern of acoustic cloak. In the formulation, the wave operator is coupled with the non-uniform velocity vector, and the equivalent source terms due to mean flow are divided into the compressibility effect and the non-uniformity effect with their own physical meanings. Numerical simulation shows the difference in far-field directivity between previous and present formulations. The polarity of the equivalent sources in the present formulation shows hexapole and skewed quadrupole patterns for non-uniformity and compressibility effects, respectively, and their magnitudes increase with power laws of Mach number as the Mach number increases. As an application, we make use of the present formulation for predicting the acoustic scattering from newly designed convective cloaks. The simulation results show better performance compared to the existing convective cloak.
在过去的十年中，大多数声学斗篷的研究都是在一个理论框架内进行的，在这个框架中，介质是静止的。然而，这样的声学斗篷不能在存在流动的情况下保持其独特的特性或功能，以使物体在声学上不可见。在本研究中，我们提出了一个理论框架，以准确研究可压缩性和非均匀性对声学斗篷散射模式的影响。在公式中，波算子与非均匀速度矢量耦合，由于平均流引起的等效源项被分为具有各自物理意义的可压缩性效应和非均匀性效应。数值模拟显示了先前和当前公式在远场指向性上的差异。本公式中的等效源极性分别呈现出非均匀性和可压缩性效应的六极和倾斜四极模式，并且随着马赫数的增加，它们的大小呈幂律增加。作为应用，我们利用本公式来预测新设计的对流斗篷的声学散射。模拟结果表明，与现有的对流斗篷相比，性能更好。
