Characterization of energy transfer and triadic interactions of coherent structures in turbulent wakes
Characterization of energy transfer and triadic interactions of coherent structures in turbulent wakes
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DOI：
10.1017/jfm.2023.641
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发表时间：
2023-09
影响因子：
3.7
通讯作者：
Dinesh Kumar Kinjangi;Daniel Foti
中科院分区：
文献类型：
--
作者：
Dinesh Kumar Kinjangi;Daniel Foti
摘要湍流尾流在不同尺度上具有明显的相干结构。它们的行为动力学可以归因于尺度间能量动力学和三元相互作用。我们开发了一种方法来量化特定尺度的动能动态。相干运动的特征在于三重分解，并用于定义平均，相干和随机速度。相干结构的具体尺度通过动态模式分解来识别，从而将总相干速度分离成按频率分类的一组速度。特定尺度的相干动能由特定尺度速度的频率三元组定义。推导了尺度相干动能平衡方程，用以解释尺度间动力学。该方法被证明在三个尾流：（i）${Re}=175$流在一个圆柱体;（ii）直接数值模拟的${Re}=3900$流在一个圆柱体;和（iii）大涡模拟的公用事业规模的风力涡轮机。圆柱尾迹的情况下，能量传递开始与旋涡脱落和能量重新分配通过高次谐波共振。特定尺度相干动能平衡量化了相干尺度、平均尺度和随机尺度之间的输运和转移分布。转子尺度中的相干动能和风力涡轮机中的轮毂涡尺度相互作用，产生新的尺度。分析表明，叶片根部的涡与短舱后面形成的轮毂涡相互作用，这对顺风近尾流中尺度的扩散有影响。
Abstract Turbulent wakes are often characterized by dominant coherent structures over disparate scales. Dynamics of their behaviour can be attributed to interscale energy dynamics and triadic interactions. We develop a methodology to quantify the dynamics of kinetic energy of specific scales. Coherent motions are characterized by the triple decomposition and used to define mean, coherent and random velocity. Specific scales of coherent structures are identified through dynamic mode decomposition, whereby the total coherent velocity is separated into a set of velocities classified by frequency. The coherent kinetic energy of a specific scale is defined by a frequency triad of scale-specific velocities. Equations for the balance of scale-specific coherent kinetic energy are derived to interpret interscale dynamics. The methodology is demonstrated on three wake flows: (i) ${Re}=175$ flow over a cylinder; (ii) a direct numerical simulation of ${Re}=3900$ flow over a cylinder; and (iii) a large-eddy simulation of a utility-scale wind turbine. The cylinder wake cases show that energy transfer starts with vortex shedding and redistributes energy through resonance of higher harmonics. The scale-specific coherent kinetic energy balance quantifies the distribution of transport and transfer among coherent, mean and random scales. The coherent kinetic energy in the rotor scales and the hub vortex scale in the wind turbine interact to produce new scales. The analysis reveals that vortices at the blade root interact with the hub vortex formed behind the nacelle, which has implications for the proliferation of scales in the downwind near wake.