Aeroacoustics_气动声学(理论教程)

Aeroacoustics 气动声学翻译：岳刚伟简介本翻译英文原文源于STAR-CCM+12.02版本的帮助文件，仅供从事CFD相关领域的同学参考，译者从2010年开始从事汽车行业的CFD仿真分析工作，本翻译根据自身的理解进行，翻译过程中错误在所难免，请予以指正。

附制作的空气动力学视频，请提出指导建议，感谢！https:///x/page/w0159lk8pka.html?https:///x/page/s0156bgaa11.html?Computational aeroacoustics (CAA) is a branch of multiphysics modeling and simulation that involves identifying noise sources that are induced by fluid flow and propagation of the subsequently generated sound waves.计算气动声学（CAA）是多体物理学的建模和仿真的一个分支，包括识别流体流动和随后产生的声波的传递而产生的噪声源。

Noise sources originate from various types of flow, such as:噪声源来自于各种类型的流动，例如：Turbulent flow over solid bodies (bluff body flows)固体表面的湍流（钝体/非线性流动）Turbulent boundary layer flows (for example, automobile, aircraft components)湍流边界层流动（例如汽车、飞机部件）High-speed turbulent shear flows (for example, free jet flow) 高速湍流切变流动（例如，自由射流）High-speed impinging flows (for example, jet impingement, rocket exhaust noise)高速撞击流（如射流冲击、火箭排气噪声）Structural vibration that is induced by fluid flow (fluid-structure interactions)由流体流动（流体与结构相互作用）引起的结构振动High-speed rotating flows (for example, rotorcrafts or turbomachinery)高速旋转流（例如，直升机或涡轮机械）Turbulent combustion (reacting flows)湍流燃烧（反应流）Blast waves (explosions)爆炸波（爆炸）A typical CAA simulation requires the following components:典型的CAA仿真需要以下组件：Navier-Stokes equations for fluid flow流体流动的纳维-斯托克方程High-resolution turbulence models高精度的湍流模型Analytical or computational acoustic wave propagationmodels解析或计算声波传播模型The noise signatures at the locations of interest exhibit corresponding noise spectra—that is, the intensities of sound pressure level over a range of frequencies. The noise characteristic can be tonal noise with a distinct peak at a frequency (such as engine noise; jet impingement noise, or Noise, Vibration, and Harshness (NVH)) or broadband noise spread over a frequency range (typical of turbulence-induced noise).关注部位的噪声特征表现出相应的噪声谱，即声压级在某一频率范围内的强度。

噪声的特性可以是离散的，在同一频率有不同的噪声峰值（如发动机噪声；射流冲击噪声，或则噪声，振动，和舒适性（NVH））或一定频率范围内传播的宽频噪声（典型的湍流引起的噪声）。

The sound pressure level (SPL measured in decibel, dB) is:声压级(SPL测量，分贝)：(3507)where:而：root mean square pressure压力均方根reference pressure (usually 20 µPa)参考压力（通常20µPa）The mechanism of noise generation differs according to the underlying physics of the flow. Thus, a computational aeroacoustics method must focus on resolving noise generation by optimizing the mesh and solver settings to capture the noise sources and frequence relevant to acoustic analysis. Resolution of the noise sources relies on the fidelity of the turbulence modeling.噪声产生的机理根据不同的流动的基础物理模型而不同。

因此，计算气动声学方法必须着眼于通过优化网格和求解器的设置来解决噪声的生成，并获取气动声学分析相关的噪声源和频率。

噪声源的精度依赖于湍流模型的准确性。

Although LES and DES simulations can predict noise generation in the near-field, they are not generally suitable for predicting noise propagation to far-field locations. The magnitudes of flowfluctuations that generate noise are orders of magnitude lower than the hydrodynamic flow properties. Without adequate mesh resolution, sound waves quickly dissipate away from the source region. The mesh density that is required to preserve this acoustic signature at far distances restricts the feasibility of pure CFD for real world applications.尽管LES和DES模拟可以预测近场产生的噪声，他们通常不适合预测噪声传播到远场的位置。

流动波动产生的噪声值的数量级低于流体流动的属性。

没有足够的网格精度，声波很快从声源区耗散。

对网格密度的要求是保证远距离的声学特征在纯CFD方法对现实世界的应用的可行性不被限定。

It is more practical to consider noise generation and propagation phenomena separately, adopting an appropriate hybrid CFD/CAA method. In this method, LES or DES is coupled (one-way) with a noise propagation aeroacoustic model.考虑噪声的产生和传播现象，采用适当的混合CFD/CAA方法更为实用。

在这种方法中，LES和DES与噪声传播的声学模型进行耦合（单向）。

Noise propagation modeling dates back to the 1950s. Sir James Lighthill [790] formulated Eqn. (3554) based on the Navier-Stokes equations and some basic assumptions, containing the definition of quadrupole noise sources from turbulent flows.噪声传播模型可以追溯到20世纪50年代。

Sir James Lighthill 基于纳维斯托克和一些基本的假定，包括湍流中四极子噪声源的定义，而建立的方程。

Following Lighthill's equation, other noise propagation models evolved considering all fundamental components of noise sources (monopole, dipole, and quadrupole), such as Curle's equation and the Ffowcs Williams-Hawkings equation (FWH). The surface integral methods such as those of the FWH method are a practical approach for noise propagation in the far-field, being able to superimpose all sources of noise over an enclosed surface and provide acoustic signatures by accurate meshless analytical solutions of a surface integral equation.下面的Lighthill方程，其他衍生的噪声的传播模型是考虑噪声源的所有基本组成（单极子，偶极子和四极子），如Curle方程和Ffowcs Williams Hawkings 方程（FWH）。