基于喷管壁面多孔处理的喷流噪声被动控制研究

Noises of jet flows exist widely in aviation and civil industries, and they are a kind of serious pollution to the working and living environments for human being. Unveiling the mechanism of the noises generated by jet flows and controlling them, are important tasks for the academic studies in aerodynamics, aeroacoustics and environmental science. In this proposal, experimental measurements of the nearfield pressure and farfield sound are combined with large eddy simulation so as to study the large scale turbulence structures and their generation, development and evolution in the shear layer of the jet. The relations between the large scale structures, the nearfield pressure fluctuations, and the farfield sound signals will be analyzed in an attempt to find the mechanisms of the sound sources. Based on the underlying relationship between turbulence structures and the sound sources, a new passive sound controlling strategy of using porous treatments on the nozzle walls will be proposed and carefully studied. The flows in both the porous media and the free zones will be mathematically modeled by using a unified set of governing equations, and the numerical methodologies for solving these equations by large eddy simulation will be discussed. The developed numerical model will be combined with experimental method to investigate the feasibility and validity of changing the initial velocity distribution in the shear layer and further influencing the large scale turbulence structures and finally reducing the noises by using porous treatments on the nozzle walls. The geometry parameters of the porous treatments will be optimized. The proposed study is aimed to develop a new method of noise controlling for the jet flows, and to contribute for guiding its possible applications.

喷流噪声在航空器以及其他工业生产部门中广泛存在，对人类的生产和生存环境造成重要的污染。喷流噪声的发生与控制是流体动力学、气动声学以及环境科学交叉领域的重要课题。本项目采用对近场压力脉动和远场声信号同步测量、同时结合大涡模拟的方法，研究喷流剪切层中大尺度湍流结构的发生、发展和演化过程，分析揭示“大尺度结构－近场压力脉动－远场声信号”之间的对应关系，研究喷流噪声声源的机理。根据湍流结构与气动声源之间的潜在关系，提出对喷管壁面进行多孔处理从而实施喷流噪声被动控制的设想，并研究具体的多孔处理实施方案。研究包含多孔几何区域和自由流动区域为一体的喷流大涡模拟的模型与方法，结合实验测量，探讨通过改变喷口附近剪切层速度的初始分布而影响湍流的大尺度结构及其强度、从而控制喷流气动噪声的可行性和有效性，寻找可供应用参考的优化参数关系。通过研究，发展喷流噪声被动控制的一种新方法和思路，并为其工程应用提供参考。

喷流噪声是一种重要的环境噪声污染，其发生与控制是流体动力学、气动声学以及环境科学等领域交叉的课题。本项目采用实验测量和大涡模拟相结合的方法，研究对喷管内壁进行多孔化处理实施喷流噪声被动控制的可行性与思路。常温下结合喷口直径D=10mm、喷流速度U=102-204m/s (对应出口马赫数Ma=0.3-0.6)的实验条件，开展了四个方面的研究，即：基线喷管的远近声场测量、圆口喷流声源流场与辐射声场的预测、喷管内壁两类多孔处理(“多盲孔”和”多孔板+容腔”)对辐射声场的影响、以及包含多孔处理和自由流场的声源流场大涡模拟。重点考察了多孔处理对声场的影响，得出了孔径1mm、孔深1-3mm盲孔以及”多孔板+容腔”中D-H-T三参数为2-7-1和3-7-1的最佳匹配。研究了适合喷流高性能大涡模拟计算的模型与算法，考察了喷流剪切层中大尺度湍流结构的发生、发展和演化过程，重点分析了“大尺度结构－近场脉动－远场声信号”之间的对应关系。研究揭示了喷管内壁两种多孔处理方式可有效地降低大尺度湍流结构的稳定性，加速其破裂和向小尺度湍流结构的转化，从而达到降低低频噪声效果的物理机理。通过研究，证明了喷管内壁多孔化处理这一被动降噪措施的可行性和有效性，找出了优化的参数，从而为工程应用实施喷流噪声的控制提供了参考依据，达到了预期的研究目标。