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Identification and analysis of the meandering of a fin-tip vortex using Proper Orthogonal Decomposition (POD)
International Journal of Heat and Fluid Flow ( IF 2.6 ) Pub Date : 2020-04-01 , DOI: 10.1016/j.ijheatfluidflow.2020.108556
Yunpeng Xue , Chetan Kumar , Soon-Kong Lee , Matteo Giacobello , Peter Manovski

Abstract The meandering of a vortex exists in a broad range of engineering applications and can lead to flow instability and other undesirable characteristics. Compared to a static vortex, measurement of a meandering vortex can result in a ‘smeared’ mean-flow field and increased levels of turbulence at the centre of the vortex. A case study was performed here on the meandering nature of a fin-tip vortex generated by a manoeuvring submarine. From stereoscopic particle image velocimetry (SPIV) measurements, it is possible to remove the meandering by shifting each instantaneous velocity field so as to produce a common centre for the vortex. In this paper, a snapshot Proper Orthogonal Decomposition (POD) technique is used to capture the dominant large-scale coherent structures (from inspection of eigenvalue or energy distributions) and to improve vortex centre identification. The POD reconstructed velocity field using only the most energetic modes enabled the coherent structures of the flow to be clearly visualised, providing improved identification of the vortex centre and subsequent evaluation of the meandering effect on the turbulent statistics. The present findings suggest that the vortex meandering only has a small impact on the ensemble-averaged resultant velocity, while contributing up to a maximum of 28% for the fluctuating component. The meandering correction also leads to an overall decrease of turbulence intensity in the peak fluctuating region of the vortex core.

中文翻译:

使用适当的正交分解 (POD) 识别和分析鳍尖涡旋的曲折

摘要 涡流的曲折存在于广泛的工程应用中,可导致流动不稳定性和其他不良特性。与静态涡流相比,蜿蜒涡流的测量会导致“模糊”平均流场和涡流中心的湍流水平增加。此处对机动潜艇产生的鳍尖涡流的蜿蜒性质进行了案例研究。从立体粒子图像测速 (SPIV) 测量中,可以通过移动每个瞬时速度场以产生涡流的公共中心来消除曲折。在本文中,快照适当正交分解 (POD) 技术用于捕获主要的大尺度相干结构(通过检查特征值或能量分布)并改进涡中心识别。POD 仅使用能量最高的模式重建速度场,使流动的连贯结构能够清晰地可视化,提供更好的涡流中心识别和随后对湍流统计的蜿蜒效应的评估。目前的研究结果表明,涡旋曲折对集合平均合成速度的影响很小,而对波动分量的影响最大为 28%。曲折修正还导致涡核峰值波动区域的湍流强度整体降低。POD 仅使用能量最高的模式重建速度场,使流动的连贯结构能够清晰地可视化,提供更好的涡流中心识别和随后对湍流统计的蜿蜒效应的评估。目前的研究结果表明,涡旋曲折对集合平均合成速度的影响很小,而对波动分量的影响最大为 28%。曲折修正还导致涡核峰值波动区域的湍流强度整体降低。POD 仅使用能量最高的模式重建速度场,使流动的相干结构能够清晰地可视化,提供更好的涡流中心识别和随后对湍流统计数据的蜿蜒效应的评估。目前的研究结果表明,涡旋曲折对集合平均合成速度的影响很小,而对波动分量的影响最大为 28%。曲折修正还导致涡核峰值波动区域的湍流强度整体降低。提供改进的涡流中心识别和随后对湍流统计数据的曲折影响的评估。目前的研究结果表明,涡旋曲折对集合平均合成速度的影响很小,而对波动分量的影响最大为 28%。曲折修正还导致涡核峰值波动区域的湍流强度整体降低。提供改进的涡流中心识别和随后对湍流统计数据的曲折影响的评估。目前的研究结果表明,涡旋曲折对集合平均合成速度的影响很小,而对波动分量的影响最大为 28%。曲折修正还导致涡核峰值波动区域的湍流强度整体降低。
更新日期:2020-04-01
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