Complex and unsteady flow patterns occur around rotating rotor blades owing to the generation of shock waves at the blade tip and interference between the blade and tip wake when the blade rotates at high speeds, thereby resulting in specific noise characteristics. Furthermore, these noise characteristics cause noise pollution in private areas and degrade detectability of helicopters in military applications. Therefore, it is important to accurately analyze noise characteristics around rotor blades. In this study, a novel computational methodology with a chimera wake grid was proposed to efficiently and accurately predict high-speed impulsive (HSI) noise due to the shock wave at the blade tip. The proposed method enables accurate analysis of a complex flow region by overlapping a wake grid in the vicinity of shock waves. A 1/7-scaled UH-1H rotor blade was used to compare and verify the accuracy of HSI noise prediction and computational efficiency. The chimera grid method was applied to the present simulation for considering the blade motion and moving effects. A permeable surface for wrapping the surface of the physical blade was constructed to include quadrupole noise source generated from the control volume, thickness noise source, and loading noise source. Furthermore, the permeable Ffowcs Williams and Hawkings (FW–H) equations were used with the Kirchhoff approach to realize efficient far-field noise prediction. The proposed HSI noise analysis via chimera wake grid indicated that the strength of the shock wave is more precisely predicted, thereby resulting in improved prediction of the HSI noise. The proposed chimera methodology allows efficient noise prediction using a much coarser background grid system.

中文翻译：

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悬停时 HSI 噪声预测网格配置的有效方法

由于叶片高速旋转时在叶片尖端产生冲击波以及叶片与尖端尾流之间的干扰，在旋转的转子叶片周围会出现复杂和不稳定的流动模式，从而导致特定的噪声特性。此外，这些噪声特性会导致私人区域的噪声污染，并降低军事应用中直升机的可探测性。因此，准确分析转子叶片周围的噪声特性非常重要。在这项研究中，提出了一种具有嵌合体尾流网格的新型计算方法，以高效准确地预测由叶尖冲击波引起的高速脉冲 (HSI) 噪声。所提出的方法通过在冲击波附近重叠尾流网格来实现对复杂流动区域的准确分析。一个1/7比例的UH-1H转子叶片被用来比较和验证HSI噪声预测的准确性和计算效率。嵌合网格方法被应用于当前的模拟以考虑叶片运动和移动效应。用于包裹物理叶片表面的可渗透表面被构造为包括由控制体积、厚度噪声源和加载噪声源产生的四极噪声源。此外，可渗透的 Ffowcs Williams 和 Hawkings (FW-H) 方程与 Kirchhoff 方法一起使用，以实现有效的远场噪声预测。通过嵌合体尾流网格提出的 HSI 噪声分析表明，更精确地预测了冲击波的强度，从而改进了对 HSI 噪声的预测。