Effect of Separation and Stall on Aerofoil Noise

众所周知，长期暴露在飞机和风力涡轮机的噪音中会造成许多生理和心理上的影响。世界卫生组织2011年估计，由于暴露于高水平噪音，西欧国家每年损失的健康生命年多达160万。这与欧盟和美国航班数量的进一步增加以及陆上风电场的发展和进一步扩张直接冲突。因此，更好地了解不同航空部件的噪声产生机制，并制定有针对性的降噪方法，以从源头上降低噪声至关重要。在所有部件中，了解机翼产生的噪声是非常重要的，因为它对飞机或风力涡轮机的整体噪声做出了贡献。在很大程度上，我们目前对翼型噪声产生的了解仅限于低迎角的翼型。然而，大多数翼型在较大的迎角下运行，以最大限度地提高气动性能，因为它们容易分离和失速，特别是当它们在各种条件下运行时。在这种情况下，与较低迎角相比，噪声的产生和流动机制有很大不同。我们对这些机制的知识和理解以及我们预测这些噪声源的能力是有限的。该合作项目包括来自工业合作伙伴的贡献，旨在对存在分离和失速的噪音产生机制进行新的理解。目标是进行实验和数值模拟，以建立一个高保真的流量和噪声数据库，适用于广泛的操作条件。这些数据将被用于确定在大迎角下导致不同翼型噪声源的流动机制。实验和数值数据也将用于开发新的完全验证的噪声预测模型，然后我们的工业合作伙伴（GE-Dowty和Embraer）可以使用这些模型来改进不同应用中的下一代举升表面的设计。总的来说，这个项目将使我们对整个系统的噪音产生机制的理解发生重大变化，并为更准确的噪音预测和制定潜在的噪音缓解策略铺平道路。

It is well established that long-term exposure to aircraft and wind turbine noise is responsible for many physiological and psychological effects. 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. This is in direct conflict with the further increase in the number of flights in the EU and US and development and further expansion of on-shore wind farms. Therefore, it is critical to better understand the noise generation mechanism from different aero-components and develop tailored noise reduction methods in order to reduce the noise at source. Amongst all components, understanding of noise generation from aerofoils is of great importance, due to its contribution to the overall noise of aircraft or wind turbine. To a great extent, our current knowledge of aerofoil noise generation is limited to aerofoils at low angles of attack. However, most aerofoils are operated at higher angles of attack to maximise aerodynamic performance where they are prone to separation and stall, especially when they are operating under varied conditions. In these situations, the noise generation as well as the flow mechanisms are substantially different compared to lower angles of attack. Our knowledge and understanding of the mechanisms as well as our ability to predict these noise sources is limited. This collaborative project, which includes contributions from industrial partners, aims to develop new understanding of noise generation mechanisms in the presence of separation and stall. The goal is to perform experiments and numerical simulations in order to establish a high-fidelity database of flow and noise for over a wide range of operating conditions. The data will then be used to identify flow mechanisms that contribute to the different aerofoil noise sources at high angles of attack. The experimental and numerical data will also be utilised to develop new fully-validated models for noise prediction, which can then be used by our industrial partners (GE-Dowty and Embraer) to improve the design of next generation of lifting surfaces across different applications. Overall, this project will bring about a step change in our understanding of noise generation mechanisms across the entire regime and pave the way to more accurate noise predictions and development of potential noise mitigation strategies.