Is the turbulent wind in convective flows driven by fluctuations?

Burr, Ulrich; Kinzelbach, Wolfgang; Tsinober, A.

doi:10.1063/1.1588638

Cited by 30 publications

(37 citation statements)

References 11 publications

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“…The numerical results in [24] show that once the mean flow is established, the temperature of the fluid is larger at one side wall and smaller at the other side, and the mean flow is driven by the mean buoyant force at the side walls. This is also in agreement with the experimental studies in [25,30].…”

Section: Introductionmentioning

confidence: 97%

Effect of large-scale coherent structures on turbulent convection

et al. 2009

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We study an effect of large-scale coherent structures on global properties of turbulent convection in laboratory experiments in air flow in a rectangular chamber with aspect ratios A ≈ 2 and A ≈ 4 (with the Rayleigh numbers varying in the range from 5 × 10 6 to 10 8 ). The large-scale coherent structures comprise the one-cell and two-cell flow patterns. We found that a main contribution to the turbulence kinetic energy production in turbulent convection with large-scale coherent structures is due to the non-uniform large-scale motions. Turbulence in large Rayleigh number convection with coherent structures is produced by shear, rather than by buoyancy. We determined the scalings of global parameters (e.g., the production and dissipation of turbulent kinetic energy, the turbulent velocity and integral turbulent scale, the large-scale shear, etc.) of turbulent convection versus the temperature difference between the bottom and the top walls of the chamber. These scalings are in an agreement with our theoretical predictions. We demonstrated that the degree of inhomogeneity of the turbulent convection with large-scale coherent structures is small.

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Section: Introductionmentioning

confidence: 97%

Effect of large-scale coherent structures on turbulent convection

et al. 2009

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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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“…1 is given in Ref. 2 and here only a brief description is presented. The experiments are performed in water in a cubic aquarium with a side length of 200 mm.…”

Section: A Experiments A: Rayleigh-bénard Convection In a Cubic Cellmentioning

confidence: 99%

“…3͒. In particular, an observation of a region of negative TKE production was made in Burr et al, 2 in which two-dimensional particle image velocimetry ͑PIV͒ was used to determine the velocity distribution in Rayleigh-Bénard convection in a cubic cell. This flow is distinct from other types of shear flows, being driven by buoyancy, and thus, particularly interesting with respect to the origin of a negative TKE production region and special effects, related to the intrinsic anisotropy and inhomogeneity of the flow.…”

Section: Introductionmentioning

confidence: 99%

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Experimental study of the structure of flow regions with negative turbulent kinetic energy production in confined three-dimensional shear flows with and without buoyancy

et al. 2005

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Regions of negative turbulent kinetic energy ͑TKE͒ production are observed and studied in two different flows, namely in turbulent thermal Rayleigh-Bénard convection in a cubic cell, and in a mechanically agitated shear flow in absence of buoyancy, with a main focus on the small scale structure of the flow. The experimental investigation is performed using three-dimensional ͑3D͒ particle tracking velocimetry, which allows for measuring the three velocity components and the full tensor of velocity derivatives in a finite 3D volume. The capability to compute the TKE production term in its complete form P =−͗u i u j ͘S ij is crucial due to the three dimensionality of the flows. A comparative analysis of four different flow situations is performed in regions with positive and negative TKE production with and without buoyancy effects. In both, convective shear flow and shear flow without buoyancy, negative TKE production is associated with the unusual, more pronounced alignment of the velocity vector u with the first eigenvector 1 S of the mean rate-of-strain tensor, related to the stretching eigenvalue, ⌳ 1 S , in contrast to the positive TKE production associated with the alignment with the third eigenvector ͑i.e., related to the negative, compressing eigenvalue͒. In the negative TKE production region of convective flow we find ͑i͒ increased values for mean strain, ͑ii͒ increased values of the first contribution P ⌳ 1 in the eigenframe of the mean rate-of-strain tensor, and decreased values of the vertical contribution to the production term in a fixed frame of reference, ͑iii͒ stronger anisotropy of u, ͑iv͒ higher levels of fluctuating strain s 2 and enstrophy 2 , as well as ͑v͒ higher rates of their production, −s ij s jk s ki and i j s ij , compared to the respective values in positive TKE production region. In the shear flow without buoyancy, all the mentioned quantities are lower in the negative TKE production region than in the positive TKE production region. From this we conclude that the inverse energy transfer in the shear flow case without buoyancy is associated with depletion of the field of velocity derivatives. This does not occur in the cubic Rayleigh-Bénard convection cell. In this flow, buoyancy is observed to have an effect on three levels: the field of velocity derivatives, velocity fluctuations, and the mean flow field. It is inferred that buoyancy is able to maintain a region with the negative TKE production by acting on all these levels simultaneously.

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Is the turbulent wind in convective flows driven by fluctuations?

Cited by 30 publications

References 11 publications

Effect of large-scale coherent structures on turbulent convection

Effect of large-scale coherent structures on turbulent convection

Large-scale instabilities in a nonrotating turbulent convection

Experimental study of the structure of flow regions with negative turbulent kinetic energy production in confined three-dimensional shear flows with and without buoyancy

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