Evolution and statistics of thermal plumes in tilted turbulent convection

Guo, Shu-Guang; Zhou, Sheng‐Qi; Qu, Lijun; Cen, Xian‐Rong; Lu, Yanjin

doi:10.1016/j.ijheatmasstransfer.2017.04.039

Cited by 17 publications

(10 citation statements)

References 41 publications

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“…In the turbulent regime, it is found that the first peak of Nu(β)/Nu(0) is due to the enhancement of the LSC, specifically the enhancement of its component in the direction of the imposed thermal gradient (y-component). The dependence of Nu and Re on large inclinations found in our study is very different in comparison to previous studies conducted in a comparable range of Ra values, in identical containers [21,22] (or containers with similar aspect ratio [19]) but with rather different Pr values. In the light of this we advance the hypothesis that the high heat-flux observed in our setup in the laminar regime depends primarily the high-Pr value.…”

Section: Discussioncontrasting

confidence: 99%

“…We remark that these results are significantly different from the ones of previous experiments in the same cell geometry at smaller Prandtl number Pr ≃ 6.3, Ra ∼ 10 9 [21] and Pr ≃ 10, Ra ∼ 10 10 [22] in which Nu monotonously decreases by 20% by increasing β. Instead a qualitatively similar double-peaked variation of Nu is found in DNS in a cylinder of aspect ratio 1 at Pr = 10 and Pr = 100, Ra = 10 7 [19].…”

Section: Heat Flux Variationcontrasting

confidence: 97%

“…Notice however that the Re l at large β could not be estimated in the experiments for the laminar regime due to the extreme weakness of the flow. Let us remark that the curves of Re is again different from the experimental results at smaller Prandtl number, where it is generally observed a peak occurring also at β ≃ 10 ± 2 o but followed by a linear decrease till the largest inclinations [19,21,22] we report also the local Reynolds number Re l from experiments is (red diamonds). In the insets: the superposed graphs for Re(β)/Re(0) (squares) and Nu(β)/Nu(0) (triangles) from DNS.…”

Section: Reynolds Number Variationcontrasting

confidence: 57%

“…In order to identify them we adopt the plumes identification procedure used in Refs. [22,44], which is based on a threshold analysis on the intensity variance of the shadowgraph images, and we then calculate the area fraction of the plumes, A p appearing in one of the corner of the experiment (inside the red square frame shown in Fig. 2g).…”

Section: Flow Patternsmentioning

confidence: 99%

“…With this in mind, in this paper we consider the still unexplored case of very large Prandtl number inclined convection cell. More precisely we focus on the dy-namics of a quasi-two-dimensional rectangular cell, the same geometry as [21,22] in a fluid with Prandtl number (Pr ≃ O(10 2 )) and at Rayleigh numbers (Ra ≃ O(10 8 )) and as before we control the flow from the developed turbulent state to the laminar state by inclining the system with β ∈ [0 o , 90 o ]. To complement the experiments and explain the observed trends, numerical simulations in very similar conditions are also carried out.…”

Section: Introductionmentioning

confidence: 99%

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Robustness of heat transfer in confined inclined convection at high Prandtl number

2019

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We investigate the dependency of the magnitude of heat transfer in a convection cell as a function of its inclination by means of experiments and simulations. The study is performed with a working fluid of large Prandtl number, Pr ≃ 480, and at Rayleigh numbers Ra ≃ 10 8 and Ra ≃ 5 × 10 8 in a quasi-two-dimensional rectangular cell with unit aspect ratio. By changing the inclination angle (β) of the convection cell, the character of the flow can be changed from moderately turbulent, for β = 0 o , to laminar and steady at β = 90 o . The global heat transfer is found to be insensitive to the drastic reduction of turbulent intensity, with maximal relative variations of the order of 20% at Ra ≃ 10 8 and 10% at Ra ≃ 5 × 10 8 , while the Reynolds number, based on the global root-meansquare velocity, is strongly affected with a decay of more than 85% occurring in the laminar regime. We show that the intensity of the heat flux in the turbulent regime can be only weakly enhanced by establishing a large scale circulation flow by means of small inclinations. On the other hand, in the laminar regime the heat is transported solely by a slow large scale circulation flow which exhibits large correlations between the velocity and temperature fields. For inclination angles close to the transition regime in-between the turbulent-like and laminar state, a quasi-periodic heat-flow bursting phenomenon is observed.

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Section: Discussioncontrasting

confidence: 99%