Partially resolved numerical simulation of flow-induced aircraft noise

这一提议的动机是欧洲有史以来最大的飞机噪音研究项目，被称为SILENCE(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，以验证从2008年起将飞机噪音降低6分贝的新技术。总预算超过1.1亿欧元。飞机噪声分为机体噪声和喷气机噪声，由于其对机场周边地区的环境影响，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机。虽然选择高涵道比的涡扇发动机可以降低喷气噪声，但在实际操作中，最大涵道比仍然受到风扇叶片长度等物理因素的限制。另一种替代方法是在喷嘴中引入楔形和片状，以牺牲发动机效率为代价来增强核心、风扇和环境气流之间的混合。人们相信，更好地了解噪声源机制，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。在此背景下，本文提出了一项研究计划，采用混合方法对机体和射流噪声进行研究，其中首先通过部分分解数值模拟获得瞬时近场流解。然后可以使用从前面的近场流解中获得的源项，使用单独的积分方法（例如，Ffowcs Williams和Hawkings方法或Kirchhoff方法）计算远场声音。

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.