Partially resolved numerical simulation of flow-induced aircraft noise

这一建议的动机是，欧洲有史以来最大的飞机噪音研究项目--SILENT(R)--于2001年4月启动。一个由51家公司组成的联盟已经合作了4年，以验证截至2008年将飞机噪音降低高达6分贝的新技术。总预算超过1.1亿欧元。飞机噪音按机身和喷气式飞机噪音分类，由于其对机场周围地区的环境影响，已成为飞机设计中越来越重要的因素。在起飞时，当发动机全速运转时，噪音的主要来源是喷气式飞机。虽然选择旁路比大的涡扇发动机可以降低喷流噪声，但在实践中，最大旁路比仍然受到风扇叶片长度等物理因素的限制。另一种方法是在喷嘴中引入人字形和凸片，以牺牲发动机效率为代价，加强核心、风扇和环境气流之间的混合。此外，人们相信，更好地了解震源机制，其中湍流起着非常重要的作用，将有助于产生新的降噪概念。正是在这种背景下，提出了一种研究方案，采用混合方法对机体和喷气噪声进行研究，首先通过部分分辨数值模拟获得瞬时近场流动解，然后利用从先前近场流动解获得的源项，使用单独的积分方法(例如Ffowcs Williams和Hawking方法或Kirchhoff方法)计算远场声场。

This proposal is motivated by the fact that the largest ever European aircraft noise research project, known as SILENCE(R), was launched in April 2001. A consortium of 51 companies have collaborated for 4 years to validate new technologies for reducing aircraft noise by up to 6 decibels (dB) as of 2008. The total budget exceeds 110 million Euros.    Aircraft noise, categorized by airframe and jet noise, has become an increasingly important factor in aircraft design due to its environmental impact on the areas surrounding airports. At takeoff, when the engine is operating at full thrust, the main source of noise is the jet. Although jet noise can be reduced by choosing a turbofan engine with a high bypass ratio, in practice, the maximum bypass ratio is still limited by physical factors such as the length of the fan blade. An alternative approach is to introduce chevrons and tabs in a nozzle to enhance mixing between core, fan and ambient air streams at the expense of engine efficiency.    It is believed that a better understanding of the source mechanism, in which turbulence plays a very important role, will facilitate the generation of new noise-reducing concepts. It is against the above background that a research program is put forward in which both airframe and jet noise will be investigated by adopting a hybrid approach, in which the instantaneous near-field flow solutions will first be obtained with Partially Resolved Numerical Simulation.  The far-field sound can then be calculated using a separate integral method (e.g., the Ffowcs Williams and Hawkings method or the Kirchhoff method) using the source terms obtained from the previous near-field flow solutions.