TOWARDS WHOLE SPECTRUM JET NOISE PREDICTION

在航空运输业快速增长的推动下，全球民用飞机机队的规模几乎每20年翻一番。英国主要机场面临越来越大的压力，需要增加额外的新跑道。飞机噪音对当地环境的影响是深远的，特别是在机场周围地区。在最坏的情况下，噪音可能不仅仅是烦人，还可能是导致高血压等疾病的一个因素。在欧洲航空研究和创新咨询委员会（ACARE）制定的最新的2050年飞行路径噪声排放目标中，到2050年，飞行飞机的感知噪声排放将相对于2000年的水平减少65%。这对航空航天工业来说是一个巨大的雄心和巨大的挑战，可能会把噪音研究推到最前沿。允许的起飞噪音水平的持续降低也使现有技术和更成熟的飞机/发动机模型过时，这对拟议的工作产生了强烈的经济影响。基于大涡模拟（LES）的射流噪声数值预测在研究领域和工业领域都有越来越大的应用前景。尽管与声学实验相比，LES预测通常更经济实惠，但它仍然耗时且昂贵，通常需要大量的高性能计算（HPC）资源，以捕获低频和高频噪声谱。这就是所谓的尺度差异，显然阻碍了基于LES的噪声预测方法进一步应用于更复杂和现实的工业喷气配置。为了克服这一尺度差异的障碍，本文提出的工作旨在探索将LES解获得的噪声光谱（在光谱空间中）与物理空间中不同网格分辨率相结合的新方法的潜在优势。目前的工作扩展了最近完成并非常成功的EPSRC项目GR/T06629/01中开发的方法，申请人是该项目的首席研究员，以及正在进行的罗尔斯罗伊斯/TSB资助的SILOET项目喷气噪声项目。从这项工作中获得的结果将与NASA的实验数据以及全长采样细网格单LES解决方案的结果进行基准比较。本工作还将通过对已分解流场的低通滤波分析、速度结构函数和湍流动能谱的评估来研究从小涡流到大涡流的湍流能量通量。

Driven by the rapid growth in air transport, the world's civil aircraft fleet is almost doubling in size every two decades. Major UK airports are under increasing pressure to add extra new runways. The impact of aircraft noise on the local environment is profound especially in the surrounding areas of an airport. In the worst case noise can be more than just annoying, potentially being a contributory factor towards illnesses such as hypertension. In the latest FlightPath 2050 noise emission targets, set by the Advisory Council for Aviation Research and innovation in Europe (ACARE), the perceived noise emission of flying aircraft is to be reduced by 65% relative to levels of 2000 by 2050. This is a huge ambition and tremendous challenge to the aerospace industry, potentially putting noise research to the forefront. Continuing reductions in permitted take-off noise levels are also making the existing technology and more established plane/engine models obsolete giving the strong economic implications for the proposed work.Large Eddy Simulation (LES) based numerical prediction of jet noise has become increasingly promising in both research communities and industry. Despite LES prediction being generally more affordable compared to acoustic experiments, it is still time consuming and costly, often requiring significant High Performance Computing (HPC) resources, in order to capture both low- and high-frequency noise spectra. This is known as the scale disparity, and clearly is preventing LES based noise predictive methods from being further applied to more complex and realistic industrial jet configurations. To circumvent this obstacle of scale disparity, the work proposed aims to explore the potential advantages of a novel approach of combining noise spectra (in the spectral space) obtained from LES solutions with different grid resolutions in the physical space. The current work extends the methodology developed in the recently completed and highly successful EPSRC project GR/T06629/01, in which the applicant being the lead researcher, and the ongoing Rolls-Royce/TSB funded SILOET programme jet noise project. Results obtained from this work will be benchmarked against NASA experimental data as well as results from a full length sampling fine-grid single LES solution. The work will also investigate turbulent energy flux directed from smaller eddies to larger ones by a low-pass filtering analysis of the resolved flow field, the evaluation of velocity structure function and turbulent kinetic energy spectra.