Computational Fluid Dynamics (CFD) of transpiration cooling and noise reduction in jet engines

近年来，由于空中交通流量的增加，机场噪声排放的减少变得更加重要。空中客车全球市场预测，未来20年全球航空运输量年增长率为4.4%。研究还得出结论，飞机噪音对人们的生活质量和健康有负面影响。仅在英国，就有100多万人生活在飞机噪音超过健康推荐水平的地区。欧洲航空研究和创新咨询委员会(ACARE)已经制定了目标，在2000年的基础上，到2050年将可感知的噪声排放减少65%。在过去，喷气发动机的噪音主要来自喷气噪音和风扇噪音。喷气噪声已通过增加涡扇发动机的旁路来降低，而风扇噪声已通过有效的声学衬垫和复杂的风扇叶片几何设计来降低。这些在降低喷气和风扇噪声方面的努力使得燃烧噪声仍然是一个重要的贡献因素。燃气轮机燃烧室系统辐射的总噪声包括“直接”噪声和“间接”噪声。湍流火焰放热速率的波动会引起不稳定的体积膨胀和收缩，从而产生压力波，从而构成“直接”的声学噪声。“间接”噪声是由于通过燃烧室，特别是涡轮叶片排的熵波加速而产生的。最近的研究表明，间接熵噪声的水平可能与直接声噪声的水平相同或更大。这需要更多地研究在涡轮叶片排中对流时未充分利用熵噪声的产生和消散。在这个PHD项目中，将使用开源软件(即OpenFoam)进行高保真的CFD分析，以研究熵波在喷嘴导叶和涡轮转子叶片排中对流时所涉及的详细流动物理。这将使我们能够了解减少间接熵噪声对燃气轮机总噪声产生的贡献的被动和主动技术。这将对设计新的燃气轮机产生重大影响，但最终会影响到受噪声排放影响的人们的生活。

In recent years, the reduction of noise emissions in airports has gained more importance due to the increase in air traffic. Airbus global market forecast predicts a 4.4% global annual air traffic growth over the next 20 years. Studies also concluded that aircraft noise has a negative impact on people's quality of life and health. In the UK alone over 1 million of people are living in areas where aircraft noise is above levels recommended for health. The Advisory Council for Aviation Research and innovation in Europe (ACARE) has set goals to reduce the perceived noise emission by 65% until 2050 with respect to the year 2000. In the past, jet engine noise was predominantly due to jet noise and fan noise. Jet noise has been reduced by increasing the bypass of turbofan engines while fan noise has been reduced through effective acoustic liners and complex designs of fan blade geometry. These efforts on the reduction of jet and fan noise have left combustion noise as an important remaining contributor. The total noise radiated by a gas turbine combustion chamber system consists of "direct" and "indirect" noise. Fluctuation in heat release rate from the turbulent flame causes an unsteady volumetric expansion and contraction, leading to a pressure wave which constitutes the "direct" acoustic noise. The "indirect" noise is generated due to the acceleration of entropy waves through the combustor, and in particular turbine blade rows. Recent studies showed that the level of indirect entropy noise could be on the same order of magnitude or larger than the direct acoustic noise. This requires more investigation of underusing the generation and dissipation of entropy noise as they convect through the turbine blade rows. In this PhD project a high fidelity CFD analisys will be performed using an open source software (i.e. OpenFoam) to investigate the detailed flow physics involved in the convection of entropy waves as they convect through the nozzle guide vane and turbine rotor blade rows. This will enable us to understand passive and active techniques to reduce the contribution of indirect entropy noise to the generation of the total noise in a gas turbine. This will have a great impact in designing new gas turbines but ultimately on peoples life affected by noise emission.