Effect of Separation and Stall on Aerofoil Noise

众所周知，长期暴露于飞机和风力涡轮机噪声中会造成许多生理和心理影响。世界卫生组织在2011年估计，由于暴露于高水平的噪音，西欧国家每年损失多达160万健康生命年。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大直接冲突。因此，更好地了解不同航空部件的噪声产生机理并开发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，由于翼型对飞机或风力涡轮机的总体噪声的贡献，了解翼型产生的噪声非常重要。在很大程度上，我们目前对翼型噪声产生的了解仅限于小迎角翼型。然而，大多数翼型在更高的迎角下运行，以最大限度地提高空气动力学性能，其中它们易于分离和失速，特别是当它们在变化的条件下运行时。在这些情况下，噪声产生以及流动机制与较低攻角相比有很大不同。我们对这些机制的了解和理解以及我们预测这些噪声源的能力是有限的。这个合作项目，其中包括工业合作伙伴的贡献，旨在发展新的认识，在分离和失速的存在下的噪声产生机制。其目标是进行实验和数值模拟，以建立一个高保真的数据库，在广泛的操作条件下的流动和噪声。这些数据将被用来确定在大迎角下产生不同翼型噪声源的流动机制。实验和数值数据还将用于开发新的经过充分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下一代升力面的设计。总的来说，该项目将使我们对整个制度中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潜在噪音缓解策略的发展铺平道路。

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.