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Axial variability of pattern formation in Rayleigh-Bénard convection: MRI velocimetry in a low aspect ratio cylinder
International Communications in Heat and Mass Transfer ( IF 7 ) Pub Date : 2020-11-01 , DOI: 10.1016/j.icheatmasstransfer.2020.104869
Matthew E. Skuntz , Brenden G. Pelkie , Sarah L. Codd , Ryan Anderson , Joseph D. Seymour

Abstract Natural convection is a fundamental hydrodynamic instability and a template process for the study of pattern formation. It is also an important mode of energy transport in natural geophysical and environmental systems, as well as technological applications. In solar heating devices, pasteurization processes, industrial mixing, and pebble-bed nuclear reactors, low aspect ratio systems of greater depth than width are widely used for their favorable convection properties. Here, magnetic resonance imaging was used to quantify the axial spatial variation of flow patterns in a narrow cylinder. Fluid velocity maps were acquired in multiple transverse and longitudinal planes. It is shown that the flow patterns vary significantly as a function of the height above the heated bottom boundary. The large scale circulation varies among predicted azimuthal mode patterns. Azimuthal 180o reorientation of the upward and downward flow cells was observed over short axial distances. The complex circulation patterns observed suggest acquisition of velocity data in only one plane could lead to mischaracterization of flow patterns in low aspect ratios systems, an aspect of the current literature which is lacking quantification. A preliminary computational fluid dynamics model in STAR-CCM+, corroborated by the experimental results, provided velocity and temperature data for the full fluid column height. Together these results indicate the need for further investigation into circulation characteristics in long narrow cylinders. Enhanced understanding of these rapid axial variations in flow pattern will allow better modeling of heat and mass transport in low aspect ratio natural convection flows.

中文翻译:

Rayleigh-Bénard 对流模式形成的轴向变化:低纵横比圆柱体中的 MRI 测速

摘要 自然对流是一种基本的流体动力学不稳定性,也是研究模式形成的模板过程。它也是自然地球物理和环境系统以及技术应用中的一种重要的能量传输方式。在太阳能加热设备、巴氏杀菌工艺、工业混合和球床核反应堆中,深度大于宽度的低纵横比系统因其有利的对流特性而被广泛使用。在这里,磁共振成像用于量化窄圆柱体中流动模式的轴向空间变化。在多个横向和纵向平面中获得流体速度图。结果表明,流动模式随加热底部边界上方的高度而显着变化。大尺度环流因预测的方位模式模式而异。在较短的轴向距离内观察到向上和向下流动池的方位角 180o 重新定向。观察到的复杂循环模式表明,仅在一个平面上获取速度数据可能会导致低纵横比系统中流动模式的错误表征,这是当前文献中缺乏量化的一个方面。STAR-CCM+ 中的初步计算流体动力学模型得到了实验结果的证实,提供了整个流体柱高度的速度和温度数据。这些结果表明需要进一步研究狭长圆柱体的循环特性。
更新日期:2020-11-01
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