航空叶轮机湍流宽频噪声仿生学降噪原理研究

After the obviousily reduction of the rotor-stator interaction tone noise, turbomachinery broadband noise is now a major contributor to the noise emission of modern high-bypass-ratio turbofan engines in use on civil aircraft. The reduction of this broadband noise is nowadays an important industrial need and probably one of the most challenging issues in turbo machinery aero acoustics..The ability to fly silently of most owl species has long been a source of inspiration for finding solutions for quieter turbomachinery. After more than a century the research regarding the mechanisms that enable the nearly silent flight of owls remains an interesting field for theoretical and experimental research. The mechanisms responsible for this are still not perfectly understood and further studies are required. .This study concerns the mechanisms the turbulence broadband noise reduction for the cascade blade.The noise reduction potential with the imitating the wing of the silent flight owl in linear cascade with different loaded airfoils will be experimentally and numerically investigated in this study. A series tests, include an open jet wind tunnel test of the model of owl wing specimen and isolated blade, compressure cascade test, and turbine cascade test, will be comparatively investigated. The LES and the Acoustics Analogy theory will be used to numerically simulate the flow field and acoustic field of the isolated blade and cascade. The leading edge and trailing edge will be remodeled to fully imitate the comb like and brush like wing feathers of the silent flight owl. The noise source identifying technique with the microphone array and the turbulence spatio-temporal information measurement means with 3D hot-wire and high frequency pressure transducer will be used in the study. The mean aerodynamic quantities, the far-field acoustics DSP, fluctuating turbulence fields will be compared for the standard straight leading- and trailing- edge case with that of the remodeled edges with the aim to reveal the physical noise reduction process. Especially, the effects of the blade-to-blade acoustic interactions, the Mach number, Reynoldes number, the ingested turbulence, as well as the interaction between ingested turbulence and trailing edge turbulence, will be experimentally and numerically investigated in the study. The goal of the current research is to understand the fundamental mechanisms controlling the broadband noise radiation of turbo machinery cascade with the imitated owl wings leading- and trailing- edge. From this research, it is also hoped, to reveal and quantify the effects of various leading- and trailing- edge configurations with imitated owl wings on the broadband noise radiation of cascade through turbulence and noise source measurements.

低噪声航空发动机设计是当前和未来航空动力技术发展的关键技术之一，也是我国重大科技专项"大型飞机"参与国际竞争的重要瓶颈技术之一。该申请项目瞄准航空叶轮机宽频噪声这一主要声源，开展基于仿生学原理的降噪理论研究，重点解决模仿寂静飞行猫头鹰翅膀细观结构的叶片湍流流动和湍流发声物理机制及理论模型等。该申请项目应用对自然现象的认识、独立叶型仿生学研究、叶栅仿生学研究等系列化的研究手段，发展从自然现象内涵物理机制到工程应用的理论和方法，弥补自然规律认识与工程应用之间理论衔接研究不足，突破湍流噪声源识别和细观构型湍流流场时空演化实验测量技术，并将独立叶型仿生学降噪理论推广到航空叶轮机叶栅的降噪等，是本项目主要创新。本项目研究内容牵涉到有关湍流发声、宽频噪声源模拟识别、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。

低噪声航空发动机设计是当前和未来航空动力技术发展的关键技术之一，也是我国“大型飞机”参与国际竞争的重要瓶颈技术之一，本项目以低噪声民用大涵道比涡扇发动机研制为背景，开展了仿生学构型叶轮机叶片湍流噪声的实验和数值模拟方法、仿猫头鹰翅膀结构降噪机理及其仿生学构造理论、模仿猫头鹰翅膀结构的航空叶轮机叶栅降噪机理、仿生学低噪声叶片气动声学设计理论和方法等研究工作。. 本项目成功地发展了基于“反方法”的传声器阵列叶片/叶栅湍流噪声源精准定位识别及声辐射定量测量的实验测试新技术，首次在国际上实现了对叶片（弦长100mm量级）前缘与尾缘噪声源和叶栅（栅距100mm量级）尾缘噪声源的精确定位识别；成功地发展了能够揭示刻画仿生学构型叶片/叶栅声学辐射的LES/FW-H混合模型和计算方法，实现了对具有仿生学构型前缘/尾缘叶片湍流宽频噪声误差不大于3dB的精确预测。. 本项目分别以“锯齿形尾缘构型”和“波浪形前缘构型”的叶片/叶栅等为重点研究对象，深入研究了猫头鹰等动物低噪声飞行本领所隐含的流动物理机理，揭示了仿生学构型对叶片声源区域湍流旋涡强度和破碎进程的影响规律，以及对声源区域湍流相位干涉的破坏机制，弄清了仿生学构型导致的叶片声源截止效应，并在主要频率范围获得了3-5dB的降噪效果。本项目还首次发现了锯齿尾缘和波浪形前缘构型降噪的关键影响参数——基于锯齿长度的无因次Strouhal数，为构建仿生学构型叶片湍流噪声分析模型奠定了重要基础。. “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，该项目正是以上述目标为出发点，发展了航空发动机气动声学实验测试新技术和噪声模拟精细方法，并发展了从自然现象内涵物理机制到工程应用的基本理论，弥补了自然规律认识与工程应用之间理论衔接的不足。本项目获得的实验测试和数值模拟新技术，取得的仿生学降噪设计新方法等，对于航空工业的突破性创新具有重要的潜在价值。