The wake of a vertical axis turbine is a type of unsteady flow with multi-scale coherent structures formed by a series of complex spatiotemporal evolutions of blade vortex shedding. The evolution characteristics and interaction of multi-scale coherent structures between two turbine wakes are the bases of multi-turbine optimal layout. In this study, the wake time series and turbine aerodynamic output were measured to explore the effect of solidity on the wake evolution characteristics of twin counter rotating vertical axis turbines. The dynamic evolution characteristics of multi-scale coherent structures in a wake were presented by a wavelet analysis. The results show that with the increase in solidity, the wake of the twin turbines gradually merges and is dominated by the shedding instability of the low-frequency large-scale structures. When the solidity remains unchanged and the chord length Reynolds number increases gradually, modulation mode structures appear between the low-frequency large-scale structures and rotation-induced structures. After the rotation-induced structures lose their coherence, energy transfers to a low frequency under the effect of modulation instability, forming self-organized large-scale structures.

中文翻译：

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强度对双反向旋转垂直轴涡轮机尾流演变特性影响的风洞试验

垂直轴涡轮机的尾流是一种具有多尺度相干结构的非定常流动，该结构由一系列叶片涡旋脱落的复杂时空演化形成。两个涡轮尾流之间的多尺度相干结构的演化特征和相互作用是多涡轮机优化布局的基础。在这项研究中，测量了尾流时间序列和涡轮机的空气动力输出，以探索固体密度对双反向旋转垂直轴涡轮机的尾流演变特性的影响。通过小波分析给出了尾波中多尺度相干结构的动态演化特征。结果表明，随着强度的增加，双涡轮机的尾流逐渐融合，并受到低频大型结构脱落失稳的支配。当强度保持不变并且弦长雷诺数逐渐增加时，调制模式结构出现在低频大尺度结构和旋转引起的结构之间。旋转引起的结构失去连贯性后，能量在调制不稳定性的作用下转移到低频，形成自组织的大型结构。