open access

https://hdl.handle.net/2115/76593

Horizontal diffusive motion of columnar vortices in rotating Rayleigh-Benard convection

英語

vortex dynamics

2019-07-25

Cambridge University Press

Journal of fluid mechanics

871

401-426

In laboratory experiments, horizontal translational motion of columnar vortices formed in rotating Rayleigh-Benard convection was investigated. Two types of measurements, vertical velocity fields and horizontal temperature fields, were conducted with water as the test fluid. Using particle image velocimetry, the vertical velocity fields determined the parameter range at which the quasi-two-dimensional columnar vortices emerged. Locally, the duration characteristics of the columns, evaluated with their vertical coherence, indicate the minimum time scale of translational motion of the vortices in the horizontal plane. Vortex tracking of the horizontal temperature fields over long observation periods (> 103 s) was conducted using encapsulated thermochromic liquid crystal visualization. Two cylindrical vessels with different radii showed the emergence of the centrifugal effect in O.> 102 s / despite the small Froude number (Fr < 0 : 1). Further, in the horizontal plane the columnar vortices behaved in a random-walk-like diffusive motion. The statistically calculated mean-squared displacements indicated anomalous diffusive motion of the columns; displacement increasing with time as t with 6D 1. We discuss the causes of this anomaly in both the instantaneous and long-term statistical data gathered from experimental observations over different time scales. The enclosure effect from the repulsion of up-welling and down-welling vortices ensures that vortices diffuse only little, resulting in a sub-diffusive (decelerated) motion < 1 in O. 101 s /. With this weak centrifugal contribution, the translational motion of the columns slowly accelerates in the radial direction and thereby yields a super-diffusive (accelerated) motion > 1 in O. (102 s).

学術雑誌論文

Accepted Manuscript

This article has been published in a revised form in Journal of fluid mechanics http://doi.org/10.1017/jfm.2019.313. This version is free to view and download for private research and study only. Not for re-distribution, re-sale or use in derivative works. © 2019 Cambridge University Press

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