航空发动机风扇MPT噪声的数值模拟研究

高涵道比发动机采用较大的风扇，叶尖相对速度更易达到超声速，从而所产生的激波噪声相当严重，已经成为航空发动机主要的噪声之一。风扇激波噪声产生的原理是激波在前传过程中会出现追赶和归并现象，表现出非线性传播特性，导致压力波形的不规则性增大，引起声能量从叶片通过频率分配到多个不同谐波。由于该问题的复杂性，理论研究大多采用二维半解析模型计算不规则波形在管道中的传播；数值研究一般采用RANS求解风扇声源区的流场，但声源区是包含激波和湍流等相互干扰的复杂流动，因此RANS方法只能用于分析定常激波噪声，难以满足非定常激波噪声的研究需求。本项目拟针对全环风扇叶片流动中产生的复杂激波噪声问题，发展基于高阶格式的URANS-DES三维非定常算法，研究叶片通道内激波的形成和演化过程，分析多重纯音噪声的产生机理，深化对多重纯音噪声产生和传播等基础问题的科学认知，为我国航空发动机的精细化降噪设计提供理论与技术支撑。

The high bypass ratio engine uses a larger fan radius, and the relative speed of the tip is more likely to reach the supersonic speed, so that the shock noise generated is quite serious and has become one of the main noises of the aero engines. The mechanism of generation for fan shock noise is that the shock wave will catch up and merge during the forward-arc process, showing nonlinear propagation characteristics, resulting in an increase in the irregularity of the pressure waveform, causing the acoustic energy to be redistributed from the blade passing frequency to a number of different EO harmonic. Due to the complexity of the problem, theoretical research mostly uses two-dimensional semi-analytical models to calculate the propagation of irregular waveforms in duct. Numerical studies generally use RANS to solve the flow field in the sound source region, but the sound source region contains shock waves and turbulence, so the RANS method can only be used to analyze the steady shock noise, and it is difficult to meet the research requirements of unsteady shock noise. This project intends to develop the URANS-DES three-dimensional unsteady method based on high-order scheme for the complex shock noise generated in the flow of full-annulus fan blades, study the formation and evolution of shock waves in the blade passage, and analyze the generation of Multiple Pure Tones (MPT) noise. The mechanism deepens the scientific understanding of the basic problems of MPT noise generation and propagation, and provides theoretical and technical support for the refined noise reduction design of aero-engines of China.