Investigating the unsteady flow mechanism at the lip of a ducted fan in crosswind

Siwei Wang, Yangang Wang, Fang Zhou, Yue Xv
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Abstract

The unsteady numerical analysis method was utilized to investigate the unsteady flow structure of a contra-rotating ducted fan under crosswind conditions. The development and evolution mechanism of the lip vortex under the combined action of crosswind and rotor were studied. Two perspectives, namely the time-averaged flow field and unsteady time-frequency analysis, were employed for the examination. The results indicate that the unsteady aerodynamic forces exerted on the lip of the ducted fan are primarily influenced by four sets of frequencies, ranked in descending order of magnitude: 1 BPF (Blade Passing Frequency) of the upstream rotor, 1 BPF of the downstream rotor, the combined effect of the 1 BPF of the upstream rotor and 1 BPF of the downstream rotor, and 2 BPF of the upstream rotor. The maximum velocity occurs at the position where the inner surface of the windward side lip is inclined 40° from the freestream velocity direction, and a stable separation vortex is formed below this region. The lip separation vortex triggers the generation of blade suction side separation vortex in the upstream rotor, and its periodic formation, growth, shedding, and dissipation are the primary factors contributing to the unsteady flow. The research findings lay the groundwork for further advancements in active and passive flow control technologies under crosswind conditions.
研究横风中管道风机唇部的不稳定流动机制
利用非稳态数值分析方法研究了横风条件下反转管道风机的非稳态流动结构。研究了横风和转子共同作用下唇涡的发展和演变机理。研究从时间平均流场和非稳态时频分析两个角度进行。结果表明,施加在管道式风机唇缘上的不稳定气动力主要受四组频率的影响,影响程度从大到小依次为:上游转子的 1 BPF(叶片通过频率)、下游转子的 1 BPF、上游转子的 1 BPF 和下游转子的 1 BPF 的综合影响以及上游转子的 2 BPF。最大速度出现在迎风侧唇内表面与自由流速度方向倾斜 40° 的位置,并在该区域下方形成稳定的分离漩涡。唇状分离涡引发了上游转子中叶片吸入侧分离涡的产生,其周期性的形成、增长、脱落和消散是造成不稳定流的主要因素。这些研究成果为进一步推进横风条件下的主动和被动流量控制技术奠定了基础。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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