Enhanced heat flux and flow structures in turbulent Rayleigh-Bénard convection with rough boundaries

Chand, Krishan; De, Arnab Kumar; Mishra, Pankaj Kumar

doi:10.1103/physrevfluids.6.124605

Cited by 9 publications

(9 citation statements)

References 40 publications

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“…2018; Chand et al. 2021 b ). In addition, we further study the dependence for other inclination angles, which have not been reported so far.…”

Section: Resultsmentioning

confidence: 99%

“…From R to R, the decrease in signifies early onset to turbulence due to a surge in plume emission (Chand et al. 2021 b ). In particular, we observe maximum improvements of , and in heat flux for the R, R, and R cases, respectively.…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…However, real-life situations are different. For instance, the presence of asperities on the surfaces and flow inside an inclined cell are some common considerations that can be seen in reality (Toppaladoddi, Succi & Wettlaufer 2015;Chand, De & Mishra 2021b;Toppaladoddi et al 2021). Owing to the application of thermal convection in industrial processes, heat exchangers and flow circulation in the atmosphere, these variants of RBC can be used to enhance heat transfer.…”

Section: Introductionmentioning

confidence: 99%

“…The present numerical set-up was used previously for solving both stationary (De & Sarkar 2020, 2021 a , b ; Chand et al. 2021 a , b ; Sharma, Chand & De 2022) and moving (Kushwaha & De 2020) boundary problems. For further details about the DIIBM, refer to De (2016, 2018).…”

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confidence: 99%

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Effect of inclination angle on heat transport properties in two-dimensional Rayleigh–Bénard convection with smooth and rough boundaries

Chand

Sharma

2022

J. Fluid Mech.

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Using direct numerical simulations, two-dimensional tilted Rayleigh–Bénard convection (RBC) is studied in both smooth and roughness-facilitated convection cells of double aspect ratio ( $\varGamma =2$ ) for air as a working fluid. We investigate the effect of inclination angle ( $0^{\circ } \leq \phi \leq 90^{\circ }$ ) on heat flux ( $Nu$ ), Reynolds number ( $Re$ ) and flow structures. In a Rayleigh number range $10^{6}\leq Ra\leq 10^{9}$ , we address the $Ra$ dependence of $Nu(\phi )$ trend. In the smooth case, while greater tilt results in highest heat flux below $Ra=10^{8}$ , $Nu$ drops with $\phi$ monotonically above it (RBC transports heat most efficiently), which explains the different $Nu(\phi )$ trend observed in the previous studies due to $Ra$ dependence (Guo et al., J. Fluid Mech., vol. 762, 2015, pp. 273–287; Shishkina & Horn, J. Fluid Mech., vol. 790, 2016, R3; Khalilov et al., Phys. Rev. Fluids, vol. 3, 2018, 043503). For the smooth case, we identify the control parameters ( $\phi =75^{\circ }$ and $Ra=10^{7}$ ) that yield maximum heat flux (an increment of $18\,\%$ with respect to the level case). On the other hand, among the three roughness set-ups used in the present study, the tallest roughness configuration yields the maximum increment in heat flux ( $25\,\%$ ) in vertical convection ( $\phi =90^{\circ }$ ) at $Ra=10^{6}$ . With increase in $Ra$ , $Re$ changes with $\phi$ marginally in the smooth case, whereas it shows notable changes in its roughness counterpart. We find that the weakening of thermal stratification is related directly to the height of roughness peaks. While $Ra$ delays the onset of thermal stratification (in terms of inclination angle) in the smooth case, an increase in roughness height plays the same role in roughness-facilitated convection cells.

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“…2018; Chand et al. 2021 b ). In addition, we further study the dependence for other inclination angles, which have not been reported so far.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Effect of inclination angle on heat transport properties in two-dimensional Rayleigh–Bénard convection with smooth and rough boundaries

Chand

Sharma

2022

J. Fluid Mech.

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A pressure-free long-time stable reduced-order model for two-dimensional Rayleigh–Bénard convection

Chand,

Rosenberger,

Sanderse

2024

Chaos: An Interdisciplinary Journal of Nonlinear Science

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The present work presents a stable proper orthogonal decomposition (POD)-Galerkin based reduced-order model (ROM) for two-dimensional Rayleigh–Bénard convection in a square geometry for three Rayleigh numbers: 104 (steady state), 3×105 (periodic), and 6×106 (chaotic). Stability is obtained through a particular (staggered-grid) full-order model (FOM) discretization that leads to a ROM that is pressure-free and has skew-symmetric (energy-conserving) convective terms. This yields long-time stable solutions without requiring stabilizing mechanisms, even outside the training data range. The ROM’s stability is validated for the different test cases by investigating the Nusselt and Reynolds number time series and the mean and variance of the vertical temperature profile. In general, these quantities converge to the FOM when increasing the number of modes, and turn out to be a good measure of accuracy. However, for the chaotic case, convergence with increasing numbers of modes is relatively difficult and a high number of modes is required to resolve the low-energy structures that are important for the global dynamics.

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Effect of isothermal rough boundaries on the statistics of velocity and temperature fluctuations in turbulent Rayleigh–Bénard convection

Chand,

Laskar,

Sharma

et al. 2023

Physics of Fluids

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Using direct numerical simulations, we investigate the effect of surface roughness on the statistics of fluctuations in a 2D rectangular cell of aspect ratio Γ = 2 with air as the working fluid. We consider roughly two decades of Rayleigh number, 108≤Ra≤4.64×109, with three roughness configurations of R1, R2, and R3 characterized by their maximum heights of 5%, 10%, and 20% of the cell height, respectively. We show that roughened cells trigger stronger fluctuations, which further gets augmented with increasing Ra. Vertical variations of velocity and temperature fluctuations show different trends. While the temperature fluctuation becomes homogeneous in the bulk, it exhibits strong inhomogeneous vertical velocity fluctuations. The comparison of global heat flux with smooth case shows a significant increment beyond Ra=2.15×108. Surface roughness impacts local heat flux through augmented plumes, which is qualitatively ascertained by instantaneous temperature field. Furthermore, probability distribution functions reveal no particular trend for the taller roughness configurations, though the magnitude is amplified. Through identification of plumes and background regions, we show their behavior as a function of Ra for different rough cases. Finally, we decompose the shear production into its three components (based on the nature of mechanical forces) to understand the energy interaction between the mean flow and fluctuating flow field.

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Enhanced heat flux and flow structures in turbulent Rayleigh-Bénard convection with rough boundaries

Cited by 9 publications

References 40 publications

Effect of inclination angle on heat transport properties in two-dimensional Rayleigh–Bénard convection with smooth and rough boundaries

Effect of inclination angle on heat transport properties in two-dimensional Rayleigh–Bénard convection with smooth and rough boundaries

A pressure-free long-time stable reduced-order model for two-dimensional Rayleigh–Bénard convection

Effect of isothermal rough boundaries on the statistics of velocity and temperature fluctuations in turbulent Rayleigh–Bénard convection

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