Dynamics of the large-scale circulation in high-Prandtl-number turbulent thermal convection

Xie, Yi-Chao; Wei, Ping; Xia, Ke‐Qing

doi:10.1017/jfm.2012.574

Cited by 23 publications

(28 citation statements)

References 39 publications

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“…The Reynolds numbers Re = 4H 2 f /ν based on the oscillation frequency f of the LSC in water and FC77 are 1.56 × 10 3 and 9.51 × 10 3 , respectively, which are in agreement with previous measurement in single-layer RBC (Lam et al 2002;Xie et al 2013). .…”

Section: Experimental Set-up and Data Analysis Methodssupporting

confidence: 90%

“…Cessation of the LSC has been well studied in previous experiments in single-layer turbulent RBC (Brown et al 2005;Brown & Ahlers 2006b;Xi et al 2006;Xi & Xia 2007;Weiss & Ahlers 2011;Xie et al 2013). In these cases, cessations are rather rare events; their frequency of occurrence is of the order of one in several days in Γ = 0.5 and 1 cells (Weiss & Ahlers 2011;Xie et al 2013).…”

Section: Cessations and Reversalsmentioning

confidence: 89%

“…The multi-thermal probe method was used to study the dynamics and coupling of the LSCs (Cioni et al 1997;Brown et al 2005;Xi & Xia 2007;Xie et al 2013). The convection cell with thermistor holders is similar to the one used by Xie et al (2013).…”

Section: Experimental Set-up and Data Analysis Methodsmentioning

confidence: 99%

“…In these cases, cessations are rather rare events; their frequency of occurrence is of the order of one in several days in Γ = 0.5 and 1 cells (Weiss & Ahlers 2011;Xie et al 2013). In Xie et al (2013), this latter situation is named decoherence. In order to acquire more statistics, a less strict definition has also been used, which requires only one of the above strengths to fall below the threshold.…”

Section: Cessations and Reversalsmentioning

confidence: 99%

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Dynamics and flow coupling in two-layer turbulent thermal convection

Xie¹,

Xia²

2013

J. Fluid Mech.

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We present an experimental investigation of the dynamics and flow coupling of convective turbulent flows in a cylindrical Rayleigh-Bénard convection (RBC) cell with two immiscible fluids, water and Fluorinert FC-77 electronic liquid (FC77). With the lighter water above FC77, the latter is under the condition of constant heat flux at its top and bottom boundaries. It is found that one large-scale circulation (LSC) roll exists in each of the fluid layers, and that their circulation planes have two preferred azimuthal orientations separated by ∼π. A surprising finding of the study is that cessations/reversals of the LSC in FC77 of the two-layer system occur much more frequently than they do in single-layer turbulent RBC, and that a cessation is most likely to result in a flow reversal of the LSC, which is in sharp contrast with the uniform distribution of the orientational angular change of the LSC before and after cessations in single-layer turbulent RBC. This implies that the dynamics governing cessations and reversals in the two systems are very different. Two coupling modes, thermal coupling (the flow directions of the two LSCs are opposite to each other at the fluid-fluid interface) and viscous coupling (the flow directions of the two LSCs are the same at the fluid-fluid interface), are identified, with the former as the predominant mode. That most cessations (in the FC77 layer) end up as reversals can be understood as a symmetry breaking imposed by the orientation of the LSC in the water layer, which remains unchanged most of the time. Furthermore, the frequently occurring cessations and reversals are caused by the system switching between its two metastable states, i.e. thermal and viscous coupling modes. It is also observed that the strength of the LSC in water becomes weaker when the LSC in FC77 rotates faster azimuthally and that the flow strength in FC77 becomes stronger when the LSC in water rotates faster azimuthally, i.e. the influence of the LSC in one fluid layer on the other is not symmetric.

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Section: Experimental Set-up and Data Analysis Methodssupporting

confidence: 90%

Section: Cessations and Reversalsmentioning

confidence: 89%

Section: Experimental Set-up and Data Analysis Methodsmentioning

confidence: 99%

Section: Cessations and Reversalsmentioning

confidence: 99%

See 2 more Smart Citations

Dynamics and flow coupling in two-layer turbulent thermal convection

Xie¹,

Xia²

2013

J. Fluid Mech.

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“…Cessations consist of a breakdown of the coherent LSC into an incoherent flow state and a subsequent re-establishment of the coherence of the LSC with a different orientation. These events are rare; they occurred at rates of the order of days −1 [31,32]. Our time series cannot reach to such durations such that a statistical analysis of cessations in liquid metal convection was not possible.…”

Section: Large-scale Flow Dynamicsmentioning

confidence: 93%

Combined measurement of velocity and temperature in liquid metal convection

et al. 2019

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Combined measurements of velocity components and temperature in a turbulent Rayleigh-Bénard convection flow at a low Prandtl number of Pr = 0.029 and Rayleigh numbers between 10 6 ≤ Ra ≤ 6×10 7 are conducted in a series of experiments with durations of more than a thousand free-fall time units. Multiple crossing ultrasound beam lines and an array of thermocouples at mid-height allow for a detailed analysis and characterization of the complex three-dimensional dynamics of the single large-scale circulation (LSC) roll in the cylindrical convection cell of unit aspect ratio which is filled with the liquid metal alloy GaInSn. We measure the internal temporal correlations of the complex large-scale flow and distinguish between short-term oscillations associated with a sloshing motion in the mid-plane with varying orientation angles of the velocity close to the top/bottom plates and the slow azimuthal drift of the mean orientation of the roll as a whole that proceeds on a hundred times slower time scale. The coherent LSC drives a vigorous turbulence in the whole cell that is quantified by direct Reynolds number measurements at different locations in the cell. The velocity increment statistics in the bulk of the cell displays characteristic properties of intermittent small-scale fluid turbulence. We also show that the impact of the symmetry-breaking large-scale flow persists to small-scale velocity fluctuations thus preventing the establishment of isotropic turbulence in the cell centre. Reynolds number amplitudes depend sensitively on beam line position in the cell such that different definitions have to be compared. The global momentum and heat transfer scalings with Rayleigh number are found to agree with those of direct numerical simulations and other laboratory experiments.arXiv:1907.03472v1 [physics.flu-dyn]

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Viscous boundary layer properties in turbulent thermal convection in a cylindrical cell: the effect of cell tilting

Wei

Xia

2013

J. Fluid Mech.

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We report an experimental study of the properties of the velocity boundary layer in turbulent Rayleigh-Bénard convection in a cylindrical cell. The measurements were made at Rayleigh numbers Ra in the range 2.8 × 10 8 < Ra < 5.6 × 10 9 and were conducted with the convection cell tilted with an angle θ relative to gravity, at θ = 0. and 3.4 o , respectively. The fluid was water with Prandtl number P r = 5.3. It is found that at small tilt angles (θ 1 o ), the measured viscous boundary layer thickness δ v scales with the Reynolds number Re with an exponent close to that for a Prandtl-Blasius laminar boundary layer, i.e. δ v ∼ Re −0.46±0.03 . For larger tilt angles, the scaling exponent of δ v with Re decreases with θ. The normalized mean horizontal velocity profiles measured at the same tilt angle but with different Ra are found to have an invariant shape. But for different tilt angles, the shape of the normalized profiles is different.It is also found that the Reynolds number Re based on the maximum mean horizontal velocity scales with Ra as Re ∼ Ra 0.43 and the Reynolds number Re σ based on the maximum rms velocity scales with Ra as Re σ ∼ Ra 0.55 , with both exponents do not seem to depend on the tilt angle θ.Several wall quantities are also measured directly and their dependency on Re are found to agree well with those predicted for a classical laminar boundary layer. These are the wall shear stress τ (∼ Re 1.46 ), the viscous sublayer δ w (∼ Re 0.75 ), the friction velocity u τ (∼ Re −0.86 ) and the skin friction coefficient c f (∼ Re −0.46 ). Again, all these near-wall quantities do not seem to depend on the tilt angle.We also examined the dynamical scaling method proposed bys Zhou and Xia [Phys. Rev. Lett. 104, 104301 (2010)] and found that in both the laboratory and the dynamical frames the mean velocity profiles show deviations from the theoretical Prandtl-Blasius profile, with the deviations increase with Ra. But profiles obtained from dynamical scaling in general have better agreement with the theoretical profile. It is also found that the effectiveness of this method appears to be independent of Ra.1. Introduction Rayleigh-Bénard convectionRayleigh-Bénard (RB) convection, which is a fluid layer heated from below and cooled from the top, is an idealized model to study turbulent flows involving heat transport and has attracted much attention during the past few decades (Siggia 1994;Kadanoff 2001;Ahlers, Grossmann & Lohse 2009;. The system is characterized by two control parameters: the Rayleigh number Ra, Prandtl number P r, which are defined arXiv:1209.6415v1 [physics.flu-dyn]

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Dynamics of the large-scale circulation in high-Prandtl-number turbulent thermal convection

Cited by 23 publications

References 39 publications

Dynamics and flow coupling in two-layer turbulent thermal convection

Dynamics and flow coupling in two-layer turbulent thermal convection

Combined measurement of velocity and temperature in liquid metal convection

Viscous boundary layer properties in turbulent thermal convection in a cylindrical cell: the effect of cell tilting

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