湍流结构与气动噪声频谱相似率关系研究

Since the foundation of aeroacoustics, the understanding of sound generation from turbulence is primarily based on acoustic analogy theory, which regards the source term as a superposition of quadrupoles or other most simple sources . Some other researchers attempted to investigate sound generation directly based on the turbulence structures. However, the dispute on sound generation mechanism from turbulent flows has never stopped for decades. To provide more comprehensive and convincing answers, it desires to accomplish detailed experiments and to develop effective methods for establishing the quantitative relations between aerodynamic noise and turbulence structures. In this project, jet noise and slat noise are selected for investigation. The generation mechanisms and propagation laws of shear-layer turbulence noise and wall-bounded turbulence noise are to be studied by using advanced testing techniques and computational aeroacoustic methods. Specifically, space-time evolution of turbulence within the source region is to be visualized by adopting Time-Resolved Particle Image Velocimetry. In addition, near-field of noise distribution and far-field noise directivity are going to be measured. Meanwhile, Large Eddy Simulation is to be accomplished to compare with the experiments. Sound-intensity-vector field from the source to far field is to be constructed by acoustic-streamline analyzing technique which is based on intensity measurements. The position and intensity of sound sources are localized and reconstructed by inverse beamforming techniques. The main focus will be on the quantitative analysis of noise spectrum similarities between the turbulence structures of different scales and near/far-field noise. Noise control methods are then to be developed based on the understanding of turbulence structures.

自气动声学学科诞生以来，对湍流发声的理解大多基于声类比理论，即假设湍流声源是由四极子等最基本的简单声源构成。尽管有研究者尝试直接基于湍流结构本身研究湍流发声，但目前对湍流发声机理的认识仍存在较大争议。倘若期望从根本上解决该问题，必须获取翔实可靠的实验数据，同时发展行之有效的定量分析方法将湍流结构和气动噪声直接关联。本项目将以喷流噪声和缝翼噪声为对象，采用先进的实验测试技术和计算气动声学方法研究剪切湍流和壁面湍流噪声产生机理与传播规律，具体通过高频响应粒子成像测速和声场测试，结合大涡模拟方法获取可靠的声源区湍流结构的时空演化规律、近声场分布和远声场特性，基于声强测量的声流线分析技术构建从声源发声向远场传播整个过程的声强矢量场，并与波束成形技术相结合确定气动声源位置和强度，重点研究并建立不同尺度湍流结构和远/近声场气动噪声频谱相似率的定量关系，进而发展有针对性的基于湍流结构的气动噪声控制方法。

喷流噪声与机体噪声是飞机噪声的主要声源之一，其发声机理和频谱相似律是重要的基础科学问题。本项目发展了谱差分+界面通量重构的计算气动声学方法、高阶格子玻尔兹曼湍流噪声模拟方法以及非负L1/2范数最小化的麦克风阵列声源定位方法等适用于复杂湍流结构发声的数值模拟与实验数据分析方法。在喷流噪声相似律研究方面，建立了基于纹影技术的喷流湍流结构与气动噪声一体化测试平台，开展了喷流湍流结构与气动噪声相似律的试验测试与数值模拟研究，揭示了超音速喷流啸音的模态转换机制及喷流-机翼安装效应的产生与辐射机理。建立了不同喷流湍流结构与气动噪声频谱相似律的定量关系及预测公式，并在此基础上发展了针对孤立喷流噪声与喷流机翼安装效应噪声的控制技术。在机体噪声相似律研究方面 ，本项目基于L1/2范数正则化的麦克风阵列声源定位方法采用该方法深入研究了缝翼噪声和襟翼侧缘噪声。实验证实了襟翼侧缘存在两个独立的非相干声源，一个声源位于襟翼侧缘的前半部分，主要产生中高频噪声；另一个声源位于襟翼侧缘的后半部分，是中低频噪声的主要来源。这两个噪声源的低频频谱都满足Strouhal数相似律，高频频谱满足Helmholtz数相似律。此外，本项目新发现了两个重要的机体噪声源，翼身结合部噪声和短舱/吊挂/缝翼结合部噪声，并分析了相应的发声机理和频谱相似律规律。研究发现：翼身结合部噪声主要是由马蹄涡和缝翼侧缘涡产生的，其噪声频谱满足Helmholtz数相似律；短舱/吊挂/缝翼结合部噪声随攻角增加而显著增加，低频满足Strouhal数相似律，高频满足Helmholtz数相似律。这些研究成果将为建立飞机噪声预测方法和开发降噪技术奠定基础。