Flow Visualization and Frequency Characteristics of Velocity Fluctuations of Complex Turbulent Flow in a Short Elbow Piping Under High Reynolds Number Condition
Flow Visualization and Frequency Characteristics of Velocity Fluctuations of Complex Turbulent Flow in a Short Elbow Piping Under High Reynolds Number Condition
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高雷诺数条件下短弯头管道内复杂湍流流动可视化及速度脉动频率特性
DOI：
10.1115/1.4007436
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
H. Yamano
中科院分区：
文献类型：
--
作者：
H. Takamura;S. Ebara;H. Hashizume;K. Aizawa;H. Yamano
通过二维粒子图像测速法对单个短弯管进行流动可视化。该管道设计为日本钠冷快堆冷段管道部分的 1/7 比例模型。这项研究描述了弯头内和下游出现的周期性运动和流动结构，并可能影响流动引起的振动。针对雷诺数从0.3 × 106到1.0 × 106的后临界状态，探索了与流动分离和流速脉动频率特性相关的流场。实验结果表明，在此范围内，流动结构并不强烈依赖于雷诺数。对斯特劳哈尔数（St）速度脉动的频率分析表明，不仅存在两种不同脱落周期的涡流，而且还存在一种周向的周期性流动。在流动分离区，周期性地发出St ≈ 0.5 的涡流，而在位于分离区和管道中心之间的剪切流区，则产生1.0 左右的涡流。另外，在分离区域附近，在圆周方向上出现了St≈0.5的周期运动。在本研究中，St 的这些值并不强烈依赖于雷诺数。
Flow visualization was performed on a single short elbow piping by means of two-dimensional particle image velocimetry. The piping was designed as a 1/7-scale model of a section of the cold-leg piping of a Japan sodium-cooled fast reactor. This study characterized the periodic motions and flow structures that appeared in and downstream of the elbow and potentially affected flow-induced vibrations. The flow field that related flow separation and frequency characteristics of the flow velocity fluctuation were explored for Reynolds number from 0.3 × 106to 1.0 × 106, which belonged to the post-critical regime. Experimental results show that flow structures are not strongly dependent on Reynolds number in this range. Frequency analysis for the velocity fluctuation in terms of Strouhal number (St) reveals that there exist not only two kinds of vortices with different shedding periods, but also one periodic flow in the circumferential direction. In the flow separation region, vortices are periodically emitted with St ≈ 0.5, while those with about 1.0 are shed in a shear flow region located between the separation region and the pipe center. Moreover, a periodic motion with St ≈ 0.5 appeared in the circumferential direction in the vicinity near the separation region. These values of St were not strongly dependent on Reynolds number in this study.