Noise Reduction through Chevron Nozzles via Multi-Point Optimization

尽管高涵道比发动机和锯齿形发动机（在发动机喷嘴后缘具有锯齿状特征）的逐步引入，但射流噪声仍然是飞机发动机噪声的重要来源。在拟议的项目中，研究了使用雪佛龙喷嘴来降低这种噪音。Chevrons可以降低飞机起飞时的噪音水平，但也会导致起飞和巡航飞行期间的推力损失。因此，必须对线形线进行优化，以最大限度地降低起飞时的噪音，并避免在巡航飞行和起飞条件下降低推力。为了解决这一问题，研究人员提出了一种新的多点推力约束噪声最小化框架，将高保真气动声学求解器与最先进的基于梯度的优化算法相结合，用于优化v形设计。通过在反向模式下使用自动微分，将为气动声学求解器实现伴随子，以便获得相对于雪佛龙形状的噪声水平的梯度信息。最重要的是，对形状进行了优化，使其远场噪声最小化，并将惩罚项纳入成本函数中，避免了推力损失。此外，伴随矩阵将用于分析识别那些声源，这些声源是飞机发动机同轴射流中主要噪声产生的原因，并被chevrons修改。研究结果将使我们更好地了解不同的v形喷管对不同飞机运行时产生的噪音和推力的影响，并为进行优化v形喷管设计提供第一个方法论基础，而不是采用试验即试的方法。

Despite the progressive introduction of high-bypass-ratio engines and Chevrons, which have a characteristic sawtooth-like shape at the trailing edge of the engine nozzle, jet noise still is a significant source of aircraft engine noise. Within the proposed project the use of chevron nozzles for such noise reduction is investigated. Chevrons can reduce the noise level during aircraft takeoff, but also can lead to thrust loss during both takeoff and cruise flight. Therefore, chevrons have to be optimized to maximize noise reduction at takeoff and avoid thrust reduction under cruise flight and takeoff conditions. To address this issue, it is proposed to develop a novel multi-point thrust-constrained noise minimization framework for optimal chevron designs, coupling a high-fidelity aeroacoustic solver withstate-of-the-art gradient-based optimization algorithms. An adjoint will be implemented for the aeroacoustic solver by using automatic differentiation in reverse mode such that gradient information of thenoise level with respect to the chevron shape will be available. Most importantly, the chevron shapes are optimized such that their far-field noise is minimized and a penalty term incorporated into the cost function avoids thrust loss. Furthermore, the adjoint will be used for an analysis to identify those sound sources, which are responsible for the major noise production in the coaxial jet from the aircraft engine and which are modified by the chevrons. The results will yield a better understanding of the impact that the various chevron nozzles have on both the noise and thrust productions at different aircraft operations and provide a first methodological basis for performing optimal chevron designs beyond the experimental cut-and-try approach.