叶轮机仿生学降噪的流动和声学机理研究

The target of this project is “to reduce noise emissions at the source, i.e. to accelerate the development of green technologies for the aircraft and its engines”. This study focuses on fundamental investigation of innovative noise control strategies and mechanisms and, ultimately, to provide aeronautic industries with applicable methodologies and technologies with a potential of achieving next step reductions in engine noise generation and emission. . . Based on the understanding on the 2-dimensional flow mechanisms and broadband noise reduction of the airfoil and planar cascade with bionic leading-edge and trailing-edge configuration, the flow and acoustic mechanisms for 3-dimensional blade and fan with bionic leading-edge and trailing-edge configuration for broadband noise reduction will be experimentally and numerically investigated in this study. A series tests, include an open jet wind tunnel test on isolated 3-dimensional blade, a sector-field compressor cascade test, and a single-stage axial-flow fan test, will be comparatively investigated. The hybrid LES and the Acoustics Analogy theory will be used to numerically simulate the flow field and acoustic field of the isolated blade, sector-field cascade and single-stage fan. The leading edge and trailing edge of the 3-dimensional blade will be remodeled with serration and wave configurations to imitate the brush like wing feathers of the silent flight owl and the leading edge tubercles of pectoral flippers of humpback whales. The new noise source identification method based on the “inverse method (Clean-SC)” of microphone array and the new hybrid LES/FW-H turbulence noise simulation method which have been developed and validated in our group will be used in this study. The turbulence spatio-temporal information measurement means with 3D hot-wire and high frequency pressure transducer will also be used in the study. Using the new noise source identification method, the separation of the leading edge noise and trailing edge noise, as well as the source distribution along the blade-span will be identified. With the hybrid LES/FW-H turbulence noise simulation method, the trailing-edge and leading-edge noise of the blade with bionics configuration were be predicted and be compared with the experimental results. The mean aerodynamic quantities, the far-field acoustics PSD, fluctuating turbulence fields will be compared for the normal leading- and trailing- edge case with that of the remodeled edges with the aim to reveal the physical noise reduction process. The effects of various leading- and trailing- edge configurations as well as the geometric parameter of the bionic configuration on the broadband noise radiation noise reduction will be revealed and quantified in the study. The effects of the flow parameter such as Mach number, Reynoldes number, the ingested turbulence on the noise reduction of the 3-dimensional blade in axial-flow fan will also be experimentally and numerically investigated.. . The goal of the current research is to understand the fundamental flow and acoustic mechanisms for 3-dimensional blade and fan with bionic leading-edge and trailing-edge configuration for broadband noise reduction. From this research, it is also hoped to find the key parameter to affect the noise reduction for the 3-dimensional blade with bionic trailing- and leading-edge configurations. The experimental technology for the identification of flow-generated noise sources and the numerical modelling methodologies for robust analysis turbomachinery turbulence noise with a potential entering into the industrial routine in design and problem diagnosis, will also be improved and developed in this study. The development of innovative noise-reduction technologies and further improvement of up-to-date experimental and numerical methodologies will be useful for the breakthrough innovation of future aviation.

“从源头上减少噪声排放，加快绿色技术在飞机和航空发动机上的应用”是目前世界范围内“绿色航空”概念的主要目标，该项目正是以此目标为出发点，研究基于仿生学原理的航空叶轮机降噪创新理论和创新方法。本项目将在已取得的二维叶型/叶栅仿生学降噪研究成果的基础上，分别从独立三维叶片、三维扇形叶栅和单级风扇等几个方面，通过对三维流动环境下精细化仿生学构型流动和声学物理机制的系列化研究，解决目前对叶轮机仿生学构型三维湍流流动机制和湍流噪声抑制机理认识不清的问题，弄清强三维流动环境下叶轮机湍流噪声辐射基本特征，揭示仿生学构型降噪的基本规律，努力探索低噪声航空叶轮机三维叶片仿生学设计理论，突破航空叶轮机湍流噪声控制这一瓶颈。本项目研究内容牵涉到湍流、湍流发声、宽频噪声源识别、仿生学细观结构湍流及声辐射等流体力学和航空科学领域重要基础理论问题，其研究成果将为未来安静航空发动机发展奠定理论基础。

航空发动机气动噪声是目前“绿色航空”技术发展的关键问题之一，也是航空大国之间竞争筹码之一。经过半个多世纪降噪技术发展，进一步降低航空发动机噪声遇到了技术瓶颈，湍流宽频噪声由于其物理机制的复杂性、湍流运动的无法避免性和普遍性，而成为当前航空发动机气动噪声控制的难点和重点。本项目以“师法自然”为灵感，以探索基于仿生学原理的航空叶轮机降噪创新理论和方法为目的，研究航空叶轮机仿生学叶片构型降噪的流动和声学物理机制，发展低噪声航空叶轮机设计原理和方法，为“超安静”航空发动机发展提供理论和技术支撑。.本项目通过系列化的实验研究和精细化的流场/声场数值模拟研究，揭示了仿生学构型设计参数、流场参数等对叶轮机转静干涉湍流宽频噪声的影响规律，研究发现，当波幅在叶片弦长的30%以内，仿生学波浪前缘总声压级降噪量随波幅/弦长之比值增大近似呈线性增加趋势；当锯齿长度在叶片弦长的20%以内，锯齿尾缘总声压级降噪量随锯齿长度/弦长之比值增大也近似呈线性增加趋势。此外，叶轮机大转折角叶栅尾缘噪声总声压级与叶栅出口气流速度6.102次方成比例，而锯齿尾缘构型明显降低了尾缘噪声，其总声压级与叶栅出口气流速度5.679次方成比例。.本项目研究结果揭示了仿生学叶片构型降低噪声的三个物理机制，即仿生学叶片构型降低了叶片表面偶极子湍流压力脉动声源强度、降低了叶片绕流湍流旋涡的展向相关性并破碎了湍流涡结构、降低了湍流噪声源在叶片展向的相干性并破坏了声源展向相位关系。基于对仿生学降噪理论的研究，本项目发展了叶轮机气动声学模型和低噪声仿生学构型发动机叶片设计理论和方法，提出了“前排叶片锯齿尾缘与后排叶片波浪前缘综合构型”、“叶片展向局部仿生学构型”等有效噪声控制方法。项目研究成果，显著提高了对湍流宽频噪声仿生学控制理论的认识水平，提升了航空发动机降噪设计的能力，为“超安静”航空发动机设计提供了新理论和新方法。