采用新型CFD辅助方法分析前缘锯齿对混流风机声学特征的形态学影响
Morphological effects of leading-edge serrations on the acoustic signatures of mixed flow fan analyzed using novel CFD-informed methods
AI总结：
本研究结合实验、CFD与FWH声类比，揭示前缘锯齿的间距、长度、倾角对混流风机气动噪声的影响规律，提出SNS可视化与SAPG指标两种声学分析新方法。
摘要：
前缘（LE）噪声是风机宽频噪声的常见来源，可通过附加前缘锯齿进行抑制。我们结合实验、计算流体动力学（CFD）和Ffowcs Williams-Hawkings（FWH）声类比方法，综合研究了受猫头鹰启发的前缘锯齿的间距、长度和倾角三种形态参数对混流风机气动声学特性的影响。基于大涡模拟结合FWH声类比，开发了一种表面噪声强度（SNS）可视化新方法，并提出了CFD辅助指标SAPG，用于通过压力梯度评估流动分离的严重程度，经证实，这两种方法可有效用于声源分析和弦向流动分离研究。声学测量结果表明，不同形态的锯齿均具备出色的权衡调节能力；SNS可视化结果显示，分离诱导的前缘噪声得到了显著抑制。三分之一倍频程分析表明，在100-3kHz频段内，增加锯齿长度比缩小间距能更有效地降低分离噪声。对于 tonal 噪声而言，更小的间距更具优势，而锯齿长度则存在最优值。此外，小倾角（低于20度）可通过流动缓冲效应减缓来流速度、缓解滞止，从而进一步抑制前缘噪声。大倾角（超过40度）会诱发额外的叶尖涡，产生高相干性湍流撞击噪声，导致4kHz以上频段的宽频噪声急剧增加。本研究阐明了前缘锯齿对旋转设备气动声学特征的形态学影响，同时为声学分析提供了实用方法。
英文摘要：
Leading-edge (LE) noise is a common source of broadband noise for fans that can be suppressed using appended LE serrations. We conduct an integrated study of the morphological effects of interval, length, and inclination angle of owl-inspired LE serrations on the aeroacoustic characteristics of a mixed flow fan using experiments, computational fluid dynamics (CFD), and the Ffowcs Williams-Hawkings (FWH) analogy. A novel method for surface noise strength (SNS) visualization was developed based on the FWH analogy with large-eddy simulations, and a CFD-informed index SAPG is proposed to evaluate the severity of flow separation with pressure gradient, which are verified to be effective in examining the acoustic sources and chordwise separation. Acoustic measurements show the robust tradeoff solving capability of the serrations under various morphologies and the SNS visualizations indicate that the separation-induced LE noise is suppressed considerably. One-third octave analyses suggest that extending serration length can lower separation noise more effectively than shrinking the interval over 100-3k Hz. A smaller interval is more desirable while an optimal length exists in association with tonal noise. Moreover, small inclination angles (below 20 degrees) enable the deceleration of oncoming flows with stagnation relieved, and consequently, further suppress the LE noise, by a flow-buffering effect. Heavy inclination angles (over 40 degrees) induce an additional tip vortex, causing high-coherence turbulence impingement noise and resulting in a drastic increase in broadband noise at frequencies exceeding 4k Hz. Our study thus clarifies the morphological effects of LE serrations on aeroacoustic signatures of rotary devices while providing useful methods for acoustic analyses.
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