Reversals of the large-scale circulation in quasi-2D Rayleigh–Bénard convection

Ni, Rui; Huang, Shi Di; Xia, Ke‐Qing

doi:10.1017/jfm.2015.433

Cited by 52 publications

(62 citation statements)

References 32 publications

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“…5. It is seen that the reversal frequencies in both cases decrease with increasing Ra, which is consistent with earlier findings in this system [29,30]. What is surprising here is that the LSC reverses its direction more frequently in the CTCT cell than in the CFCT cell, despite the fact that in the former the LSC is stronger and the temperature fluctuations in its BL are smaller.…”

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confidence: 92%

“…Therefore, the temperature contrast δ = T right − T lef t will change its sign during a reversal event and thus is a good indicator of reversals [29], where T right and T lef t are the temperatures measured by the thermistors imbedded in the right and left sides of the plate. To discuss the reversal frequency quantitatively, we first define the start and end times of one reversal event when δ changes its sign, from which we obtain the time interval between two successive reversals [30]. The reversal frequency is then calculated by taking the inverse of the mean time interval of successive reversals.…”

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confidence: 99%

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Comparative Experimental Study of Fixed Temperature and Fixed Heat Flux Boundary Conditions in Turbulent Thermal Convection

Huang

Wang

et al. 2015

Phys. Rev. Lett.

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confidence: 92%

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confidence: 99%

Comparative Experimental Study of Fixed Temperature and Fixed Heat Flux Boundary Conditions in Turbulent Thermal Convection

Huang

Wang

et al. 2015

Phys. Rev. Lett.

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“…This phenomenon has a high relevance for explaining polarity reversals of the geomagnetic field and changes of wind direction in earth's atmosphere. Various models have been proposed to explain * tasaka@eng.hokudai.ac.jp the nature of such reversals taking account of the randomness from thermal turbulence [6][7][8].…”

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confidence: 99%

Regular flow reversals in Rayleigh-Bénard convection in a horizontal magnetic field

et al. 2016

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Magnetohydrodynamic Rayleigh-Bénard convection was studied experimentally using a liquid metal inside a box with a square horizontal cross section and aspect ratio of five. Systematic flow measurements were performed by means of ultrasonic velocity profiling that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two-dimensional rolls arranged parallel to the magnetic field. The number of rolls has the tendency to decrease with increasing Rayleigh number Ra and to increase with increasing Chandrasekhar number Q. We explored convection regimes in a parameter range, at 2 × 10 3 < Q < 10 4 and 5 × 10 3 < Ra < 3 × 10 5 , thus extending the regime diagram provided by Yanagisawa et al. [T. Yanagisawa et al., Phys. Rev. E 88, 063020 (2013)]. Three regimes were identified, of which the regime of regular flow reversals in which five rolls periodically change the direction of their circulation with gradual skew of the roll axes can be considered as the most remarkable one. The regime appears around a range of Ra/Q = 10, where irregular flow reversals were observed in Yanagisawa et al. We performed the proper orthogonal decomposition (POD) analysis on the spatiotemporal velocity distribution and detected that the regular flow reversals can be interpreted as a periodic emergence of a four-roll state in a dominant five-roll state. The POD analysis also provides the definition of the effective number of rolls as a more objective approach.

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“…Each flow field contained 127 × 127 velocity vectors and a total of 10 000 vector maps were acquired with a sampling rate ∼2 Hz. The statistical behaviour of flow reversal, a phenomenon that the LSC suddenly reverses its flow direction in an erratic manner (Sreenivasan, Bershadskii & Niemela 2002;Xi & Xia 2007), were studied with the so-called temperature contrast method (Sugiyama et al 2010;Ni, Huang & Xia 2015). For ease of presentation, the details of this technique will be described in § 3.1.…”

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confidence: 99%

Effects of geometric confinement in quasi-2-D turbulent Rayleigh–Bénard convection

Huang

Xia

2016

J. Fluid Mech.

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We report an experimental study of confinement effects in quasi-2-D turbulent Rayleigh-Bénard convection. The experiments were conducted in five rectangular cells with their height H and length L being the same and fixed, while the width W was different for each cell to produce lateral aspect ratios (Γ = W/H) of 0.6, 0.3, 0.2, 0.15 and 0.1. Direct flow field measurements reveal that the large-scale flow slows down as Γ decreases and there are more plumes travelling through the bulk region. Moreover, the reversal frequency of the large-scale flow is found to increase drastically in smaller Γ cells, by more than 1000-fold for the highest value of Rayleigh number reached in the experiment. The reversal frequency can be well described by a stochastic model developed by Ni et al. (J. Fluid Mech., vol. 778, 2015, R5) and the probability density functions (PDF) of the time interval between successive reversals are found to follow Poisson statistics as in the 3-D system. It is further observed that the bulk temperature fluctuation increases significantly and its PDF changes from exponential to Gaussian as Γ decreases. The influences of geometric confinement on the global heat transport are also investigated. The measured Nu-Ra relationship suggests that, as the lateral aspect ratio decreases, the relative weight of the boundary layer contribution in the global heat transport increases compared to that from the bulk. These results demonstrate that in the quasi-2-D geometry, geometric confinement has strong effects on both the global and local properties in turbulent convective flows, which are very different from the previous findings in 3-D and true 2-D systems.

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Reversals of the large-scale circulation in quasi-2D Rayleigh–Bénard convection

Cited by 52 publications

References 32 publications

Comparative Experimental Study of Fixed Temperature and Fixed Heat Flux Boundary Conditions in Turbulent Thermal Convection

Comparative Experimental Study of Fixed Temperature and Fixed Heat Flux Boundary Conditions in Turbulent Thermal Convection

Regular flow reversals in Rayleigh-Bénard convection in a horizontal magnetic field

Effects of geometric confinement in quasi-2-D turbulent Rayleigh–Bénard convection

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