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Wake dynamics behind a rotary oscillating cylinder analyzed with proper orthogonal decomposition
Ocean Engineering ( IF 5 ) Pub Date : 2020-12-01 , DOI: 10.1016/j.oceaneng.2020.108185
Huan Ping , Hongbo Zhu , Kai Zhang , Rui Wang , Dai Zhou , Yan Bao , Zhaolong Han

Abstract Two-dimensional high-order spectral/hp computations are carried out for a cylinder undergoing a sinusoidal rotary oscillation about its own axis. Results are examined for R e = 200 and a fixed oscillation amplitude of θ 0 = π . The study concentrates on a domain of forcing frequencies ranging from 0 to 5 f 0 , with f 0 being the natural shedding frequency of the fixed cylinder. The drag of the cylinder is measured to reduce by up to 22% at the optimal frequency. This drag reduction is expected to result from the appearance of negative pressure in the windward regions of cylinder surface. Proper orthogonal decomposition (POD) is then utilized to extract the energetic modes that govern the dynamics of the flow. A novel force decomposition technique proposed by Miyanawala and Jaiman (2019) is reformulated, to allow quantification of the time-dependent contribution from each mode to the pressure drag. Such contribution is found to be affected, in a manner, by the forcing frequency. POD is further used to characterize the spatially evolving nature of the forced wake as it undergoes a transition from the near-wake two-layer shedding pattern to the far-wake Karman-like shedding pattern. It is also found that a few modes suffice to reconstruct the near-wake accurately, while more modes must be retained to ensure an accurate approximation of the far-wake.

中文翻译:

用适当的正交分解分析旋转振荡圆柱体后面的尾流动力学

摘要 对绕自身轴进行正弦旋转振荡的圆柱体进行了二维高阶谱/马力计算。针对 Re = 200 和 θ 0 = π 的固定振荡幅度检查结果。该研究集中在范围从 0 到 5 f 0 的强迫频率域,其中 f 0 是固定圆柱体的自然脱落频率。在最佳频率下,气缸的阻力经测量可减少多达 22%。预计这种阻力减少是由于气缸表面迎风区域出现负压所致。然后利用适当的正交分解 (POD) 来提取控制流动动力学的能量模式。重新制定了 Miyanawala 和 Jaiman (2019) 提出的一种新的力分解技术,允许量化每个模式对压力阻力的时间相关贡献。发现这种贡献以某种方式受到强迫频率的影响。POD 进一步用于表征强迫尾流的空间演化性质,因为它经历了从近尾流两层脱落模式到远尾尾流类卡门脱落模式的过渡。还发现少数模态足以准确地重建近尾迹,而必须保留更多模态以确保精确逼近远尾迹。POD 进一步用于表征强迫尾流的空间演化性质,因为它经历了从近尾流两层脱落模式到远尾尾流类卡门脱落模式的过渡。还发现少数模态足以准确地重建近尾迹,而必须保留更多模态以确保精确逼近远尾迹。POD 进一步用于表征强迫尾流的空间演化性质,因为它经历了从近尾流两层脱落模式到远尾尾流类卡门脱落模式的过渡。还发现少数模态足以准确地重建近尾迹,而必须保留更多模态以确保精确逼近远尾迹。
更新日期:2020-12-01
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