Abstract Highly-swept blades are used in automotive cooling systems, in the fans of modern ultra-high by-pass ratio engines and in counter-rotating open rotors, in part in order to reduce noise emission. The present work investigates the effect of sweep on the free-field noise emission from the trailing edge of an isolated airfoil analytically, as a first step towards a more complete approach dedicated to rotating blades. Firstly, Amiet-Schwarzschild’s technique is extended to the case of a swept airfoil in order to assess the effect of sweep on the sound directivity both by a single three-dimensional gust and by the combined effect of all gusts at a given frequency. It is found that sweep produces a non-symmetric directivity pattern, similar to the effect of a skewed gust. Sweep also affects the wavenumber distribution of the wall-pressure fluctuations beneath a turbulent boundary layer. This effect is studied by means of a generalised Corcos’ model, which allows distributing energy in the chordwise and spanwise wavenumber ranges independently. The role of the spanwise-wavenumber distribution of wall-pressure power spectral density in amplifying the radiated noise is investigated and shown to have a limited impact.

中文翻译：

---

后掠翼型后缘声源和声辐射的分析模型

摘要 高后掠叶片用于汽车冷却系统、现代超高涵道比发动机的风扇和反向旋转的开式转子，部分是为了减少噪音排放。目前的工作以分析的方式研究了扫掠对孤立翼型后缘自由场噪声发射的影响，这是迈向更完整的旋转叶片方法的第一步。首先，Amiet-Schwarzschild 的技术扩展到后掠翼型的情况，以评估单一三维阵风和给定频率下所有阵风的组合效应对声音方向性的影响。发现扫掠会产生非对称的方向性图案，类似于倾斜阵风的效果。扫描也影响湍流边界层下壁面压力波动的波数分布。这种效应是通过广义 Corcos 模型研究的，该模型允许在弦向和展向波数范围内独立分布能量。研究了壁压力功率谱密度的展向波数分布在放大辐射噪声中的作用，并表明其影响有限。