Significance of near-wall dynamics in enhancement of heat flux for roughness aided turbulent Rayleigh–Bénard convection

Chand, Krishan; Sharma, Mukesh; De, Arnab Kumar

doi:10.1063/5.0053522

Cited by 11 publications

(12 citation statements)

References 31 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…2018; Chand et al. 2021 a ). Also, all the roughness elements are buried under a thick thermal boundary layer.…”

Section: Resultsmentioning

confidence: 99%

“…This happens because roughness elements in R become active at this () and perturb the thermal boundary layer to modify the flow structures by directly injecting thermal plumes in the bulk (Chand et al. 2021 a ). On the other hand, owing to their relatively shorter height with respect to the thermal boundary layer, roughness elements in the other two cases remain buried inside it.…”

Section: Resultsmentioning

confidence: 99%

“…(2018) and Chand et al. (2021 a ) identified the critical roughness height and critical Rayleigh number, respectively, beyond which heat flux increases.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, rough surface has been exploited to achieve the enhanced heat flux (Toppaladoddi, Succi & Wettlaufer 2017; Zhang et al. 2018; Chand, Sharma & De 2021 a ; Chand et al. 2021 b ; Toppaladoddi et al.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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.

Self Cite

View full text Add to dashboard Cite

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.

show abstract

“…2018; Chand et al. 2021 a ). Also, all the roughness elements are buried under a thick thermal boundary layer.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

“…(2018) and Chand et al. (2021 a ) identified the critical roughness height and critical Rayleigh number, respectively, beyond which heat flux increases.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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.

Self Cite

View full text Add to dashboard Cite

show abstract

“…At the highest , the above-mentioned error diminishes to , which emphasizes the excellent spatial resolution used for the larger cases. This numerical set-up has been used for a number of complex flows that involve stationary (De & Sarkar 2020; Chand, Sharma & De 2021) and moving (De & Sarkar 2021 a , b ) boundaries.…”

mentioning

confidence: 99%

Investigation of flow dynamics and heat transfer mechanism in turbulent Rayleigh–Bénard convection over multi-scale rough surfaces

Sharma

Chand

2022

J. Fluid Mech.

View full text Add to dashboard Cite

We present a two-dimensional numerical study of turbulent Rayleigh–Bénard convection with air as the working fluid over a multi-scale randomly roughened surface in a rectangular box of aspect ratio 2 over three decades of Rayleigh number ( $10^8 \leq {\textit {Ra}} \leq 10^{11}$ ). With varied response of the roughness elements at different ${\textit {Ra}}$ , enhanced heat transfer scaling ( $\gamma =0.41$ ) is retained throughout the explored ${\textit {Ra}}$ range. The plume emission process is triggered from the taller roughness elements at a lower ${\textit {Ra}}$ , while smaller elements contribute significantly at higher ${\textit {Ra}}$ . Increased plume emission frequency compared to the smooth case is reflected from the enhanced volume fraction and thermal dissipation rate of plumes. The tip of the roughness elements exhibits the highest temperature and vertical velocity fluctuations, while washing out of the trapped fluid in the throat region holds the key to enhanced heat flux at higher ${\textit {Ra}}$ . Increased localized pockets of fluid at higher ${\textit {Ra}}$ indicate better inter-scale energy transfer, which is reflected in higher energy content at all scales in the computed temperature spectra. The decomposition of the flow field into orthogonal modes reveals that heat transfer enhancement at higher ${\textit {Ra}}$ is associated with multiple small-scale structures. Owing to better energy transfer and intense localized fluctuations, modal distribution of energy is less severe for higher ${\textit {Ra}}$ , and stable twin large-scale rolls do not favour an efficient heat transport process.

show abstract

Study on the heat transfer enhancement of self-excited oscillating pulsating flow by the boundary vortex group

et al. 2022

View full text Add to dashboard Cite

In this work, the self-excited oscillating pulsating circular pipe is the object of study. Based on the flow evolution characteristics of boundary layer and vortex, the mechanism of enhanced heat transfer by self-excited oscillating pulsating flow is investigated. Moreover, a vital flow structure, the boundary vortex ring (BVR for short), is proposed. The study results show that the vortex evolution within the shear layer inside the self-excited oscillating pulsating chamber has an important influence on the formation of the downstream boundary vortex ring. Both have the same period but different phases. The boundary vortex group formed by the BVR is distributed at intervals in the pipe, and its role in promoting fluid flow increases first and then decreases. At the same time, the strength of the central mainstream area is gradually strengthened. The boundary vortex group's flow state determines the downstream pipe's heat transfer characteristics. The low-velocity zone on both sides determines the position of the heat transfer coefficient enhancement, and the central vorticity determines the amplitude of the enhancement. The boundary vortex group with a complete structure can effectively promote heat transfer, while the boundary vortex group with an incomplete structure can suppress heat transfer. The time-averaged boundary layer thickness increase ratio δ' and the time-averaged equal diameter circular tube performance evaluation index ηT provide the fundamental indexes for designing and optimizing variable cross-section heat transfer circular tubes. Furthermore, the heat transfer coefficient of the tube wall varies synchronously with the thickness of the boundary layer.

show abstract

Significance of near-wall dynamics in enhancement of heat flux for roughness aided turbulent Rayleigh–Bénard convection

Cited by 11 publications

References 31 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

Investigation of flow dynamics and heat transfer mechanism in turbulent Rayleigh–Bénard convection over multi-scale rough surfaces

Study on the heat transfer enhancement of self-excited oscillating pulsating flow by the boundary vortex group

Contact Info

Product

Resources

About