Abstract The self-noise of an isolated controlled-diffusion aerofoil is investigated using direct noise computations. The high-order finite difference solver HiPSTAR is used to conduct four large eddy simulations and one direct numerical simulation. The motivation is to investigate the multiple sources of aerofoil self-noise on a realistic compressor blade geometry, the physical mechanisms leading to the generation of sound, and the influence of compressibility effects. The angle of attack is 8°, the chord-based Reynolds number is 105, and results obtained for four values of the free-stream Mach number [0.2, 0.3, 0.4, 0.5] are compared. For those flow parameters, the pressure side is fully laminar, whereas a separation bubble is present on the suction side close to the leading edge that promotes transition to turbulence. The size of the separation bubble is found to increase with the Mach number. Two noise sources are observed, one at the trailing edge and one in the leading edge transition/reattachment region. The first has a broadband, low frequency spectrum, while the second displays a tone whose frequency depends on the local Mach number. Because the leading edge separation bubble is very small, the associated tone frequency is high and requires a significantly finer grid to faithfully resolve the acoustic propagation than what is typically deemed sufficient. Finally, cross correlations between the surface pressure and the far-field pressure reveal that the pressure fluctuations reaching the trailing edge are initially generated in the transition/reattachment region, which indicates that the trailing edge noise is a consequence of the pressure fluctuations generated by the separation bubble.

中文翻译：

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受控扩散翼型的不同噪声产生机制及其对马赫数的依赖

摘要 使用直接噪声计算研究了隔离受控扩散翼型的自噪声。使用高阶有限差分求解器 HiPSTAR 进行 4 次大涡模拟和 1 次直接数值模拟。其动机是研究真实压缩机叶片几何结构上机翼自噪声的多个来源、导致声音产生的物理机制以及可压缩性效应的影响。攻角为 8°，基于弦的雷诺数为 105，比较了自由流马赫数 [0.2, 0.3, 0.4, 0.5] 四个值的结果。对于这些流动参数，压力侧是完全层流的，而靠近前缘的吸力侧存在分离气泡，促进过渡到湍流。发现分离气泡的大小随着马赫数的增加而增加。观察到两个噪声源，一个在后缘，一个在前缘过渡/重新附着区域。第一个具有宽带、低频频谱，而第二个显示频率取决于本地马赫数的音调。由于前缘分离气泡非常小，相关的音调频率很高，并且需要比通常认为足够的网格更精细的网格来忠实地解析声学传播。最后，表面压力和远场压力之间的互相关表明，到达后缘的压力波动最初是在过渡/重附着区域产生的，