From laminar plumes to organized flows: the onset of large-scale circulation in turbulent thermal convection

Xi, Heng-Dong; Lam, Siu; Xia, Ke‐Qing

doi:10.1017/s0022112004008079

Cited by 210 publications

(152 citation statements)

References 31 publications

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“…Mesoscale circulations very likely correspond to the thermal winds observed in all laboratory experiments on convection (e.g., Krishnamurti and Howard, 1981;Sano et al, 1989;Niemela et al, 2001;Xi et al, 2004, and references therein). The phenomenology of this process has been shown to be very subtle, as several authors argue that the flow results from a nonlinear clustering process (Xi et al, 2004;Parodi et al, 2004) …”

Section: Local Hydrodynamic Cartesian Simulations: Mesoscale Dynamicsmentioning

confidence: 65%

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The Sun’s Supergranulation

Rincon

Rieutord

2010

Living Rev. Solar Phys.

163

132

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The Sun's supergranulation refers to a physical pattern covering the surface of the quiet Sun with a typical horizontal scale of approximately 30,000 km and a lifetime of around 1.8 d. Its most noticeable observable signature is as a fluctuating velocity field of 360 m s -1 rms whose components are mostly horizontal. Supergranulation was discovered more than fifty years ago, however explaining why and how it originates still represents one of the main challenges of modern solar physics.A lot of work has been devoted to the subject over the years, but observational constraints, conceptual difficulties and numerical limitations have all concurred to prevent a detailed understanding of the supergranulation phenomenon so far. With the advent of 21st century supercomputing resources and the availability of unprecedented high-resolution observations of the Sun, a stage at which key progress can be made has now been reached. A unifying strategy between observations and modelling is more than ever required for this to be possible.The primary aim of this review is therefore to provide readers with a detailed interdisciplinary description of past and current research on the problem, from the most elaborate observational strategies to recent theoretical and numerical modelling efforts that have all taken up the challenge of uncovering the origins of supergranulation. Throughout the text, we attempt to pick up the most robust findings so far, but we also outline the difficulties, limitations and open questions that the community has been confronted with over the years.In the light of the current understanding of the multiscale dynamics of the quiet photosphere, we finally suggest a tentative picture of supergranulation as a dynamical feature of turbulent magnetohydrodynamic convection in an extended spatial domain, with the aim of stimulating future research and discussions.

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Section: Local Hydrodynamic Cartesian Simulations: Mesoscale Dynamicsmentioning

confidence: 65%

“…The phenomenology of this process has been shown to be very subtle, as several authors argue that the flow results from a nonlinear clustering process (Xi et al, 2004;Parodi et al, 2004) …”

Section: Local Hydrodynamic Cartesian Simulations: Mesoscale Dynamicsmentioning

confidence: 99%

The Sun’s Supergranulation

Rincon

Rieutord

2010

Living Rev. Solar Phys.

163

132

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“…du Puits et al 2007 and references therein). Only recently, two-dimensional cuts through the flow field have been analysed by combining particle image velocimetry and shadowgraph techniques (Xi, Lam & Xia 2004).…”

Section: Introductionmentioning

confidence: 99%

Fine-scale statistics of temperature and its derivatives in convective turbulence

Emran

Schumacher

2008

J. Fluid Mech.

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We study the fine-scale statistics of temperature and its derivatives in turbulent RayleighBénard convection. Direct numerical simulations are carried out in a cylindrical cell with unit aspect ratio filled with a fluid with Prandtl number equal to 0.7 for Rayleigh numbers between 10 7 and 10 9 . The probability density function of the temperature or its fluctuations is found to be always non-Gaussian. The asymmetry and strength of deviations from the Gaussian distribution are quantified as a function of the cell height. The deviations of the temperature fluctuations from the local isotropy, as measured by the skewness of the vertical derivative of the temperature fluctuations, decrease in the bulk, but increase in the thermal boundary layer for growing Rayleigh number, respectively. Similar to the passive scalar mixing, the probability density function of the thermal dissipation rate deviates significantly from a log-normal distribution. The distribution is fitted well by a stretched exponential form. The tails become more extended with increasing Rayleigh number which displays an increasing degree of small-scale intermittency of the thermal dissipation field for both the bulk and the thermal boundary layer. We find that the thermal dissipation rate due to the temperature fluctuations is not only dominant in the bulk of the convection cell, but also yields a significant contribution to the total thermal dissipation in the thermal boundary layer. This is in contrast to the ansatz used in scaling theories and can explain the differences in the scaling of the total thermal dissipation rate with respect to the Rayleigh number.

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“…They usually embrace the entire convective boundary layer (of the order of 1-3 km in height) and include pronounced convergence flow patterns close to the surface. In the sheared convective flows, the structures represent largescale rolls (cloud streets) stretched along the mean wind [1,2,12] Coherent structures in convective turbulent flows were comprehensively studied theoretically, experimentally and in numerical simulations [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28]. However, some aspects related to the origin of large-scale coherent structures in non-rotating turbulent convection are not completely understood.…”

Section: Introductionmentioning

confidence: 99%

Large-scale instabilities in a nonrotating turbulent convection

2006

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A theoretical approach proposed in Phys. Rev. E 66, 066305 (2002) is developed further to investigate formation of large-scale coherent structures in a non-rotating turbulent convection via excitation of a large-scale instability. In particular, the convective-wind instability that causes formation of large-scale coherent motions in the form of cells, can be excited in a shear-free regime. It was shown that the redistribution of the turbulent heat flux due to non-uniform large-scale motions plays a crucial role in the formation of the coherent large-scale structures in the turbulent convection. The modification of the turbulent heat flux results in strong reduction of the critical Rayleigh number (based on the eddy viscosity and turbulent temperature diffusivity) required for the excitation of the convective-wind instability. The large-scale convective-shear instability that results in the formation of the large-scale coherent motions in the form of rolls stretched along imposed large-scale velocity, can be excited in the sheared turbulent convection. This instability causes the generation of convective-shear waves propagating perpendicular to the convective rolls. The mean-field equations which describe the convective-wind and convective-shear instabilities, are solved numerically. We determine the key parameters that affect formation of the large-scale coherent structures in the turbulent convection. In particular, the degree of thermal anisotropy and the lateral background heat flux strongly modify the growth rates of the large-scale convective-shear instability, the frequencies of the generated convective-shear waves and change the thresholds required for the excitation of the large-scale instabilities. This study elucidates the origins of the large-scale circulations and rolls in the atmospheric convective boundary layers and the meso-granular structures in the solar convection.

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From laminar plumes to organized flows: the onset of large-scale circulation in turbulent thermal convection

Cited by 210 publications

References 31 publications

The Sun’s Supergranulation

The Sun’s Supergranulation

Fine-scale statistics of temperature and its derivatives in convective turbulence

Large-scale instabilities in a nonrotating turbulent convection

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