Aeroacoustics of Dynamic Stall

众所周知，长期暴露在飞机和风力涡轮机噪声中会造成许多生理和心理影响。根据最近的研究，噪音不仅影响舒适性、生活质量、生产力和学习，而且还增加了因中风、冠心病和心血管疾病而住院和死亡的风险。世界卫生组织在2011年估计，在西欧国家，由于暴露在高水平的噪音中，每年损失的健康寿命年多达160万年。政府也承认，机翼噪声限制了航空公司机队的增长、城市空气流动性的可接受性、风力涡轮机的运行和扩张，对英国经济有直接影响。就空气动力噪声而言，机翼噪声可能是许多应用中最重要的噪声源之一。虽然翼型旨在通过在大迎角下运行来实现最大的气动性能，但由于不断变化的流入条件(阵风、风切变、尾流相互作用)，它们不可避免地更容易受到流动分离和失速的影响。分离和失速会导致气动性能的急剧降低和气动噪声的显著增加。在涉及旋转叶片的应用中，当叶片受到高度动态流入时，叶片的近失速运行会引起一种更复杂的现象，称为动态失速。虽然最近对动态失速空气动力学的研究表明了问题的复杂性，但由于在实验、数值和分析方法方面的长期挑战，对动态失速噪声产生的理解一直停滞不前。这个合作项目包括来自强大的工业和学术咨询委员会的贡献，旨在加深对动态失速流动和噪声的新理解，并开发控制动态失速噪声的技术。该团队将利用致力于动态失速空气声学的最先进的实验台和GPU加速的高保真CFD工具，在广泛的操作条件(流速、俯仰频率/幅度等)下为俯仰翼型生成史无前例的大量流动和噪声数据。然后，这些数据将被用来识别在大迎角下导致不同翼型噪声源的流动机制，包括翼型非定常加载和流动四极子源，以及动态失速制度的详细分类。还将开发一套新的频域和时间域分析工具，用于预测不同动态失速区域下的动态失速噪声，并提供高保真的实验和数值数据。这个项目将使我们对各种操作中的翼型俯仰噪声的理解发生重大变化，并为更准确的噪声预测和开发潜在的噪声缓解策略铺平道路。

It is well established that long-term exposure to aircraft and wind turbine noise is responsible for many physiological and psychological effects. According to the recent studies, noise not only creates a nuisance by affecting amenity, quality of life, productivity, and learning, but it also increases the risk of hospital admissions and mortality due to strokes, coronary heart disease, and cardiovascular disease. The World Health Organization estimated in 2011 that up to 1.6 million healthy life years are lost annually in the western European countries because of exposure to high levels of noise. The noise is also acknowledged by governments as a limit to both airline fleet growth, acceptability of Urban Air Mobility, operation and expansion of wind turbines, with direct consequences to the UK economy.With regards to aerodynamic noise, aerofoil noise is perhaps one of the most important sources of noise in many applications. While aerofoils are designed to achieve maximum aerodynamic performance by operating at high angles of attack, they become inevitably more susceptible to flow separation and stall due to changing inflow conditions (gusts, wind shear, wake interaction). Separation and stall can lead to a drastic reduction in aerodynamic performance and significantly increased aerodynamic noise. In applications involving rotating blades, the near-stall operation of blades, when subjected to highly dynamic inflows, gives rise to an even more complex phenomenon, known as dynamic stall. While the very recent research into the aerodynamics of dynamic stall has shown the complexity of the problem, the understanding of dynamic stall noise generation has remained stagnant due to long-standing challenges in experimental, numerical and analytical methods. This collaborative project, which includes contributions from strong industrial and academic advisory boards, aims to develop new understanding of dynamic stall flow and noise and develop techniques to control dynamic stall noise. The team will make use of the state-of-the-art experimental rigs, dedicated to aeroacoustics of dynamic stall and GPU-accelerated high-fidelity CFD tools to generate unprecedented amount of flow and noise data for pitching aerofoils over a wide range of operating conditions (flow velocity, pitching frequency/amplitude, etc.). The data will then be used to identify flow mechanisms that contribute to the different aerofoil noise sources at high angles of attack, including aerofoil unsteady loading and flow quadrupole sources, and detailed categorisation of dynamic stall regimes. A set of new frequency- and time-domain analytical tools will also be developed for the prediction of dynamic stall noise at different dynamic stall regimes, informed by high-fidelity experimental and numerical datasets. This project will bring about a step change in our understanding of noise from pitching aerofoils over a wide range of operations and pave the way to more accurate noise predictions and development of potential noise mitigation strategies.