ABSTRACT Three-dimensional unsteady wake characteristics have been investigated numerically in flow past surface mounted finite-height rectangular cylinder using Open Source Field Operation and Manipulation. Effect of impinging shear (shear intensity, K) on transitional characteristics of wake flow has been studied using iso-Q surfaces for Reynolds number (Re) in the range from 150 to 250. Various flow regimes, such as steady flow, symmetric and asymmetric modes of vortex shedding have been identified based on the values of Re and K for different side ratios (SR) of the cylinder. Unsteady wake oscillations have been analyzed using time signal of transverse velocity component in the wake. These signals have been decomposed into different component signals using Hilbert-Huang transformation (HHT). Variation of frequency and energy density with time of the decomposed signals has been presented in the form of Hilbert spectra. Effects of Re, SR and K on wake oscillation frequency have been illustrated in the form of marginal spectra. Time-delay reconstructions and Poincare sections have been examined to study periodic and aperiodic nature of the wake flow. Non-stationarity associated with the wake fluctuation is quantified in terms of degree of stationarity. Symmetric and asymmetric modes have been confirmed using singular value decomposition of the vorticity field and presented using dynamic modes. Growth rate and frequency of the modes corresponding to symmetric shedding are found to be lower than those for asymmetric shedding. In addition, variation in mean drag coefficient has been reported with change in Re and K for each value of SR.

中文翻译：

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切变流引起的表面贴装矩形圆柱体的尾流过渡

摘要 已经使用开源场操作和操纵在流过表面安装的有限高度矩形圆柱体中对三维不稳定尾流特性进行了数值研究。已经使用雷诺数 (Re) 在 150 到 250 范围内的 iso-Q 表面研究了撞击剪切（剪切强度，K）对尾流过渡特性的影响。 各种流态，例如稳态流、对称流和非对称流已经根据圆柱体不同侧比 (SR) 的 Re 和 K 值确定了涡旋脱落模式。使用尾流中横向速度分量的时间信号分析了非定常尾流振荡。这些信号已使用 Hilbert-Huang 变换 (HHT) 分解为不同的分量信号。已分解信号的频率和能量密度随时间的变化以希尔伯特谱的形式呈现。Re、SR 和 K 对尾流振荡频率的影响已以边缘谱的形式进行了说明。已经检查了时间延迟重建和庞加莱截面，以研究尾流的周期性和非周期性。与尾流波动相关的非平稳性以平稳度来量化。对称和非对称模式已使用涡量场的奇异值分解得到确认，并使用动态模式呈现。发现对应于对称脱落的模式的增长率和频率低于非对称脱落的那些。此外，据报道，对于每个 SR 值，平均阻力系数随 Re 和 K 的变化而变化。