Reduced-order modelling of jet noise using a map-based stochastic turbulence approach

喷气发动机以不同的方式产生噪音，但这种噪音主要来自从发动机后部喷嘴流出的高速废气。飞机在缓慢移动时声音最大，比如起飞或降落时。当废气流遇到相对静止的空气时，它会产生巨大的剪切力，很快就会变得不稳定。对新的降噪概念性能的评估主要依赖于对相关马赫数流区中声过程的源机制进行建模的稳健而又经济的数值方法。这项研究的目的是为了更好地了解高频范围内的丢失噪声，这表现出较高的恼人惩罚和有限的频率带宽预测，并开发一种模拟工具来预测相同的噪声。这一建议通过一种基于地图的随机降阶建模方法促进了后者。模拟喷流湍流等复杂现象需要使用极高分辨率的网格来表示所涉及的动力学。一个典型的模拟可能有5亿个网格点。将其乘以5，以计算压力、密度和三个速度分量，以描述每个网格点上的流动。这相当于数十亿个自由度或计算机用来模拟单一理想化喷气式飞机噪音的变量数量。这里出现的一个重要问题是，这些负担得起的高分辨率数值模拟的当前状况是否可以进一步发展，以回答关于喷气噪声的剩余问题。在拟议的研究中，我建议开发一种降阶建模方法，这种方法具有独特的可能性，可以结合详细和可分辨的物理，目的是提高该水平上的模拟结果的保真度。预期研究的结果将是一个有科学依据的喷气噪声预测模型，涉及由降维模型产生的合成压力场。更广泛地说，这项研究旨在证明对湍流射流压力场的可靠预测，其影响远远超出了本研究的范围。

Jet engines produce noise in different ways, but mainly this noise comes from the high-speed exhaust stream that leaves the nozzle at the rear of the engine. And planes are loudest when they move slowly, such as at takeoff or landing. As the exhaust stream meets relatively still air, it creates tremendous shear that quickly becomes unstable. The evaluation of the performance of new noise-reducing concepts crucially depends on robust but economical numerical methods for modelling of source mechanisms of the acoustic processes in the relevant Mach number flow regimes. The purpose of this research proposal is to gain a better understanding of the missing noise in the range of high-frequencies, which exhibits a high annoyance penalty, and limited frequency bandwidth predictions and to develop a simulation tool to predict the same. This proposal contributes to the later via a map-based stochastic reduced-order modelling approach. Simulating a complex phenomenon like jet turbulence requires the use of an extremely high-resolution mesh to represent the dynamics involved. A typical simulation could have 500 million grid points. Multiply that by five to account for pressure, density and three components of velocity to describe the flow at every grid point. That equates to billions of degrees of freedom or the number of variables a computer uses to simulate the noise from a single idealised jet. The important question that arises here is whether the current status of these affordable high-resolution numerical simulations can be evolved further to answer the remaining questions about jet noise. In the proposed research, I propose the development of a reduced-order modelling approach that has a unique possibility to incorporate detailed and resolved physics with the aim of increasing the fidelity of the simulation results on that level.The outcome of the intended research will be a jet noise prediction model that is scientifically well-grounded, involving a synthetic pressure field generated by the reduced-order model. More broadly, the research is intended to demonstrate reliable prediction of the pressure field of a turbulent jet, with implications well beyond the scope of the present study.