Identification of the Linear Sound Sources in Turbulent free Shear Flows:Non-modal Analysis and Direct Numerical Simulation Study

湍流自由剪切流中线性声源的识别：非模态分析和直接数值模拟研究

• 批准号: 261830592
• 负责人: Professor Dr.-Ing. Holger Foysi
• 金额: --
• 依托单位: Lehrstuhl für Strömungsmechanik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2018-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/261830592?language=en
• 关键词: Identification; Linear; Sound; Sources; Turbulent

The linear process of sound generation by pure vortex mode perturbations embedded in mixing layer and jet flows is the main objective of the proposed research which is based on a theoretical breakthrough in the hydrodynamic stability theory of shear flows in the 1990s. This breakthrough is related to the understanding of phenomena induced by the non-normality of non-uniform flow systems and it enables us to study the linear sound generation processes. Our preliminary results show that the only linear mechanism of wave generation by vortex disturbances is the mode coupling induced by the non-normality of these flow systems. This mechanism is efficient for all Mach numbers and the near field of the generated sound is comparable to the hydrodynamic one: the energy of the linearly generated acoustic waves in shear flows is comparable to the energy of the turbulent eddies. The non-modal approach (Kelvin-mode approach) is the basic theoretical approach in our study and allows us to analyse the basic processes of linear sound generation by vortices embedded in the flows under investigation. It is also known that the sound field reveals an anisotropic nature in the spectral space and the topology of the linear source representation in Lighthill's acoustic analogy and of the presented mechanism of anisotropic linear wave generation are inherently different and principally incompatible with each other. Accordingly, we consider free shear flows to understand the basic physics of the underlying phenomena of sound generation in these flows. Therefore, the main aim of the project is the comprehensive and quantitative investigation of the efficiency of linear phenomena in sound generation. The analysis of the relative roles of linear and nonlinear processes in the generation and propagation of acoustic waves in the free shear flow will also be the focus of this proposal.

基于90年代剪切流水动力稳定性理论的突破，本文研究的主要目标是混合层和射流中嵌入纯涡模扰动的线性发声过程。这一突破涉及到对非均匀流系统非正态现象的理解，使我们能够研究线性发声过程。我们的初步结果表明，涡旋扰动产生波浪的唯一线性机制是由这些流动系统的非正态引起的模式耦合。这种机制对所有的马赫数都是有效的，并且产生的声音的近场与流体动力学的相当：剪切流中线性产生的声波的能量与湍流涡旋的能量相当。非模式方法(开尔文模式方法)是我们研究的基本理论方法，它使我们能够分析嵌入在所研究的流动中的涡旋产生线性声音的基本过程。众所周知，声场在频谱空间中表现出各向异性的性质，莱特希尔声学类比中线性源表示的拓扑结构和所提出的各向异性线性波产生机制的拓扑结构本质上是不同的，并且基本上彼此不兼容。因此，我们考虑自由剪切流，以了解在这些流中声音产生的基本物理现象。因此，该项目的主要目标是全面和定量地研究线性现象在声音产生中的效率。分析线性和非线性过程在自由剪切流中声波的产生和传播中的相对作用也将是本提案的重点。