AI 中文总结
本研究通过混合RANS/LES和FW-H声学类比，揭示悬停旋翼中频准音调噪声源于叶片二次涡相互作用（BSVI），并确认其为非周期音调噪声的新来源，对旋翼飞行器声学设计有重要意义。
AI 中文摘要
近期针对小型悬停旋翼的室内实验报告称，即使在无尾流再循环的情况下，残余（非周期）远场声谱中仍存在来源不确定的中频准音调峰值。本研究利用混合雷诺平均纳维-斯托克斯/大涡模拟结合Ffowcs Williams-Hawkings声学类比，对四叶片理想扭转悬停旋翼进行了研究，以探究其物理来源。高分辨率模拟再现了实测的高次谐波叶片通过频率音调，证实其源于旋翼流场本身，而非封闭舱室测试环境。流场分析将这些音调归因于叶片二次涡相互作用（BSVI）：约在r/R=0.88至0.96之间的外侧叶片截面，反复受到由前序叶片主梢涡卷入尾流剪切层而形成的相干S形二次涡虫的撞击。这些非周期二次涡产生叶片间相关的载荷，形成区别于纯周期叶片涡相互作用和主要随机叶片尾流相互作用噪声的准音调特征。对零平均上洗流进行谱本征正交分解证实，中频（3-10 kHz）成分由与涡辫相关的单一低秩空间相干模态主导，而接近1 kHz的低频模态则与主梢涡核心相关。因此，BSVI被确定为悬停旋翼中一种独特且此前未表征的非周期音调噪声源，对中小型旋翼飞行器和电动垂直起降推进器的声学设计具有直接影响。
英文摘要
Recent indoor experiments on small-scale hovering rotors have reported mid-frequency quasi-tonal peaks of uncertain origin in the residual (aperiodic) far-field sound spectrum, even without wake recirculation. This study investigates their physical origin using hybrid Reynolds-averaged Navier-Stokes/large-eddy simulations coupled with a Ffowcs Williams-Hawkings acoustic analogy, applied to a four-bladed ideally twisted rotor in hover. The high-resolution simulation reproduces the measured higher-harmonic blade-passage-frequency tones, confirming that they arise from the rotor flow itself and not from the enclosed-chamber test environment. Flow-field analysis attributes the tones to blade secondary vortex interaction (BSVI): the outboard blade sections, between approximately r/R = 0.88 and 0.96, are repeatedly impinged upon by coherent, S-shaped secondary vortex worms formed by entrainment of the wake shear layer into the primary tip vortices of preceding blades. These aperiodic secondary vortices produce blade-to-blade correlated loading, yielding a quasi-tonal signature distinct from both purely periodic blade-vortex interaction and mostly stochastic blade-wake interaction noise. Spectral proper orthogonal decomposition of the zero-mean upwash confirms that the mid-frequency (3-10 kHz) content is dominated by a single, low-rank, spatially coherent mode associated with the braids, whereas a lower-frequency mode near 1 kHz is linked to the primary tip vortex core. BSVI is thus identified as a distinct and previously uncharacterized source of aperiodic tonal noise in hovering rotors, with direct implications for the acoustic design of small- to medium-scale rotorcraft and electric vertical take-off and landing propulsors.
