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Experimental investigation of upstream cube effects on the wake of a wall-mounted cylinder: Wake rising reduction, TKE budget and flow organization
European Journal of Mechanics - B/Fluids ( IF 2.5 ) Pub Date : 2021-01-21 , DOI: 10.1016/j.euromechflu.2021.01.004
Maëlys Magnier , Philippe Druault , Grégory Germain

The development of Marine Renewable Energy based on tidal currents at a selected area needs to first analyze the flow characteristics and thus the bathymetry induced turbulence in this area. The present study aims to investigate turbulence characteristics around two wall mounted obstacles in tandem, which represent seabed obstacles in a high Reynolds number flow. 2D planar PIV measurements are performed in multiple planes to access the main flow organization. Based on successive analyses of mean flow characteristics as well as of the flow organization, it is demonstrated that the presence of an upstream cube clearly impacts the cylinder wake development by preventing the rising of the large scale flow structures observed for an isolated wall-mounted cylinder in the same flow conditions. The TKE budget analysis shows that the energy is mainly produced in the upstream cube shear layer, and TKE exchanges are very small in the far wake field, in comparison with a single cylinder flow configuration. A Fourier analysis shows that the cube–cylinder interaction generates a low frequency peak in the far wake field which persists for long downstream distances. This particular frequency is the signature of the cylinder wake coherent structures. A statistical analysis based on the two-point correlation velocity tensor confirms that energetic flow structures present in the far wake are mainly of 2D nature and develop horizontally. Elongated structures are identified in the wake and seem to correspond to hairpin-like structures. Instantaneous vortex structures are also characterized with local vortex identification swirling strength criterion, confirming previous FFT and statistical results. The impact of the upstream cube is strongest in the near wake in the symmetrical transverse plane and prevents the large scale flow structures from rising in the water column.



中文翻译:

上游立方效应对壁挂式汽缸尾流的实验研究:尾流上升减少,TKE预算和流动组织

在选定区域以潮流为基础的海洋可再生能源的发展需要首先分析该区域的流量特性,然后进行测深法引起的湍流。本研究旨在调查串联安装的两个壁挂障碍物周围的湍流特征,这些障碍物代表高雷诺数流中的海床障碍物。在多个平面中执行2D平面PIV测量以访问主流结构。基于对平均流动特性以及流动组织的连续分析,证明了上游立方体​​的存在通过防止对孤立的壁挂式气缸观察到的大规模流动结构的上升而明显影响了气缸尾流的发展。在相同的流量条件下。TKE预算分析表明,能量主要产生于上游的立方剪切层,与单缸流动配置相比,TKE交换在远场中非常小。傅立叶分析表明,立方体与圆柱体的相互作用会在远尾波场中产生一个低频峰,并在下游长距离处持续存在。该特定频率是圆柱尾波相干结构的特征。基于两点相关速度张量的统计分析证实,远流中存在的高能流结构主要具有二维性质,并且是水平发展的。细长的结构被识别出并似乎对应于发夹状结构。瞬时涡旋结构的特征还在于局部涡旋识别涡旋强度准则,确认先前的FFT和统计结果。上游立方体​​的冲击在对称横断面的近尾流处最强,可防止大型流动结构在水柱中升起。

更新日期:2021-02-02
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