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，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。这与欧盟和美国航班数量的进一步增加以及陆上风力发电场的开发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，开发有针对性的降噪方法，从源头上降低噪声是至关重要的。在所有部件中，了解翼型产生的噪声非常重要，因为它对飞机或风力涡轮机的整体噪声有贡献。在很大程度上，我们目前关于翼型噪声产生的知识仅限于小攻角的翼型。然而，大多数翼型在更大的攻角下运行，以最大限度地提高气动性能，特别是当它们在不同的条件下运行时，它们容易分离和失速。在这些情况下，噪声的产生以及流动机制与较小的攻角相比有很大的不同。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。该合作项目包括工业合作伙伴的贡献，旨在发展对分离和失速情况下噪声产生机制的新理解。其目标是进行实验和数值模拟，以便为各种操作条件建立一个高保真的流动和噪声数据库。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。实验和数值数据还将被用来开发新的全面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升力表面的设计。总体而言，该项目将改变我们对整个制度中噪声产生机制的理解，并为更准确地预测噪声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. 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.