Article
Mechanics
Shashwat Bhattacharya, Thomas Boeck, Dmitry Krasnov, Joerg Schumacher
Summary: We investigate how fringing magnetic fields affect turbulent thermal convection in a horizontally extended rectangular domain. By controlling the gap between the magnetic poles and the convection cell, we vary the fringe width and observe the changes in large-scale structures and heat transport. We find that as the local vertical magnetic field strength increases, the structures become thinner and align perpendicular to the sidewalls.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Jian-Chao He, Yun Bao, Xi Chen
Summary: Direct numerical simulation (DNS) is conducted for non-slip two dimensional (2D) Rayleigh-Benard convection (RBC) with a wide range of Rayleigh number (Ra up to 10^13), Prandtl number Pr 1/4 0.7, and aspect ratio gamma= 1. The thermal dissipation rate shows an evident scaling transition at Ra asymptotic to 10^9. The mean temperature gradient in the thermal boundary layer is the dominant contribution to the transition. The Nusselt number also exhibits the transition at Ra asymptotic to 10^9. Rating: 7/10.
Article
Mechanics
Mebarek Belkadi, Anne Sergent, Yann Fraigneau, Berengere Podvin
Summary: The study uses three-dimensional direct numerical simulations to characterize turbulent buoyant convection in a water-filled valley Rayleigh-Benard cavity, identifying three distinct heat transfer regimes with transitional regime II exhibiting intense heat transfer, larger temperature fluctuations, and a larger friction coefficient compared to regimes I and III.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Shengqi Zhang, Xin Chen, Zhenhua Xia, Heng-Dong Xi, Quan Zhou, Shiyi Chen
Summary: This study investigated the control of large-scale circulation in turbulent Rayleigh-Benard convection using two-point and four-point control with locally isothermal sidewalls through numerical simulations. The results showed that the control effect depends on the distance of control area, control configurations, and flow dimensions.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Thomas Wondrak, Max Sieger, Rahul Mitra, Felix Schindler, Frank Stefani, Tobias Vogt, Sven Eckert
Summary: In this paper, an experimental study on the manifestation and dynamics of large-scale circulation (LSC) in turbulent liquid metal convection is reported. By using contactless inductive flow tomography and multi-thermal-probe methods, the three-dimensional flow structures and temperature variations induced by LSC are measured and analyzed. The results reveal that the stability of single-roll LSC increases and the flow structures with multiple rolls decrease with the increase of Rayleigh numbers.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Lu Zhang, Guang-Yu Ding, Ke-Qing Xia
Summary: This paper investigates the influence of horizontal buoyancy on heat transport in turbulent thermal convection through experimental and numerical studies, revealing that horizontal buoyancy increases both vertical and horizontal heat transport. The horizontal Nusselt number is found to be approximately one order of magnitude smaller than the vertical Nusselt for the parameter range explored.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Jian-Lin Yang, Yi-Zhao Zhang, Tian-cheng Jin, Yu-Hong Dong, Bo-Fu Wang, Quan Zhou
Summary: The effects of the Prandtl number on the critical roughness height in turbulent Rayleigh-Benard convection are divided into three regimes: low Pr, moderate Pr, and high Pr. The variations in the critical roughness height are influenced by the thickness of thermal boundary layers and the competition between corner-flow rolls and large-scale circulation. Ultimately, the convective flow transitions to the plume-controlled regime at high Pr.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Gerardo Paolillo, Carlo Salvatore Greco, Tommaso Astarita, Gennaro Cardone
Summary: This study presents a time-resolved experimental investigation of turbulent Rayleigh-Benard convection inside a cylinder with one-half aspect ratio, using water as the working fluid. The results show that low-order POD modes are closely related to the formation of a large scale circulation (LSC) in a single-roll or double-roll state. Innovative criteria based on POD analysis are proposed to identify the instantaneous flow state accurately.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Sebastian Moller, Theo Kaeufer, Ambrish Pandey, Joerg Schumacher, Christian Cierpka
Summary: Turbulent superstructures in horizontally extended three-dimensional Rayleigh-Benard convection flows are investigated in controlled laboratory experiments in water at Prandtl number Pr = 7. The experimental results confirm that the superstructure patterns are an important backbone of the heat transfer.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Marcel Wedi, Dennis P. M. van Gils, Eberhard Bodenschatz, Stephan Weiss
Summary: This study reports turbulent thermal convection experiments in a rotating cylinder, revealing changes in heat transport and temperature field at different rotation rates, as well as proposing interpretations for two transition points in the rotation rates. The research findings provide insights into the behavior of turbulent thermal convection in a rotating system.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Alexander Blass, Pier Tabak, Roberto Verzicco, Richard J. A. M. Stevens, Detlef Lohse
Summary: In this paper, the authors report the results of direct numerical simulations of sheared Rayleigh-Benard convection, investigating the influence of different Reynolds numbers, Prandtl numbers, and bulk Richardson numbers on flow structures. The study shows that the Prandtl number strongly influences the morphology and dynamics of flow structures in the turbulent wall sheared thermal convection.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Hao-Ran Liu, Kai Leong Chong, Rui Yang, Roberto Verzicco, Detlef Lohse
Summary: In this study, we numerically investigate the influence of gas bubbles attached to the hot plate on turbulent Rayleigh-Benard convection. The existence of bubbles reduces the overall heat transfer and changes the boundary layer structure. We observe asymmetric temperature profiles under different parameter conditions, which can be quantitatively explained based on heat flux conservation. We propose the idea of using an equivalent single-phase setup to mimic the system with attached bubbles and validate the predictions by comparing with numerical results. The results can be applied to predict mass transfer in other fields, such as water electrolysis or catalysis.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Yi-Zhen Li, Xin Chen, Ao Xu, Heng-Dong Xi
Summary: This study presents an experimental investigation of the large-scale vortex in turbulent Rayleigh-Benard convection. The vortex center exhibits periodic orbiting in the shape of an ellipse, and the flow forms a vortex tube filling the cylindrical cell.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Yun-Bing Hu, Yi-Chao Xie, Ke-Qing Xia
Summary: This study experimentally investigates the effect of centrifugal force on turbulent rotating Rayleigh-Benard convection. The results show that the centrifugal effect depends on the Rayleigh number and flow states, providing important insights for predicting heat transport.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Andreas D. Demou, Mehdi Niazi Ardekani, Parisa Mirbod, Luca Brandt
Summary: This study presents direct numerical simulations of turbulent Rayleigh-Benard convection in non-colloidal suspensions, with special focus on the heat transfer modifications in the flow. The research found that the Nusselt number weakly but steadily increases when the particle volume fraction is below 25%, mainly due to increased thermal agitation. However, when the particle volume fraction exceeds 30%, the Nusselt number exhibits a substantial drop, attributed to the dense particle layering in the near-wall region, which reduces convection and inhibits the formation of coherent structures near the wall.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Ao Xu, Xin Chen, Heng-Dong Xi
Summary: A numerical study on flow states and reversals in a two-dimensional circular Rayleigh-Benard cell revealed a new chaotic flow state, with the primary roll becoming stronger as Ra increases, while LSC reversals are accompanied by growth in secondary rolls. The phase diagram in Ra-Pr space shows that circulation states occur at large Ra and small Pr, and LSC reversals are limited to a specific range of Pr. Competition between thermal and viscous diffusions explains the phase diagram. Global properties such as Nusselt and Reynolds numbers are affected by internal flow states.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Shengqi Zhang, Xin Chen, Zhenhua Xia, Heng-Dong Xi, Quan Zhou, Shiyi Chen
Summary: This study investigated the control of large-scale circulation in turbulent Rayleigh-Benard convection using two-point and four-point control with locally isothermal sidewalls through numerical simulations. The results showed that the control effect depends on the distance of control area, control configurations, and flow dimensions.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Multidisciplinary Sciences
Yi-Bao Zhang, Eberhard Bodenschatz, Haitao Xu, Heng-Dong Xi
Summary: The addition of a minute amount of long-chain flexible polymer in turbulent flow can significantly alter flow properties, such as reducing drag and enhancing mixing. The interaction between polymer additives and eddies of different spatial scales changes turbulent energy transfer. The presence of a previously unidentified scaling range, known as the elastic range, affects the scaling of high-order velocity statistics and has important implications for various turbulence systems.
Article
Mechanics
Dongpu Wang, Hechuan Jiang, Shuang Liu, Xiaojue Zhu, Chao Sun
Summary: The study investigates the relationship between flow structure, heat transfer, and asymmetric average temperature fields with the radius ratio in the annular centrifugal Rayleigh-Bénard convection system. It was found that with increasing radius ratio, the zonal flow weakens and the heat transfer efficiency increases.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Yi-Zhen Li, Xin Chen, Ao Xu, Heng-Dong Xi
Summary: This study presents an experimental investigation of the large-scale vortex in turbulent Rayleigh-Benard convection. The vortex center exhibits periodic orbiting in the shape of an ellipse, and the flow forms a vortex tube filling the cylindrical cell.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Ao Xu, Ben-Rui Xu, Li-Sheng Jiang, Heng-Dong Xi
Summary: In this study, we numerically investigate the production and transport of vorticity in two-dimensional Rayleigh-Benard convection. The flow structure and temperature distribution are found to be greatly influenced by the interaction of multiple vortices. Besides vorticity produced by wall shear stress, buoyancy also plays a significant role in generating vorticity in the bulk region. The produced vorticity is then transported through advection and diffusion. The visualization of buoyancy-produced vorticity contours allows for the observation of main and corner vortices. The correlation between the spatial distribution of vorticity flux along the wall and the Nusselt number suggests a direct relationship between the amount of vorticity entering the flow and the amount of thermal energy entering the flow.
Article
Mechanics
Ao Xu, Hua-Lin Wu, Heng-Dong Xi
Summary: A numerical study is conducted to train a self-propelling agent to migrate in an unsteady flow environment. The results show that the smart agent can learn to migrate efficiently by utilizing background flow currents, and the training process is more challenging in turbulent flow compared to simple periodic flow.
Article
Mechanics
Dongpu Wang, Shuang Liu, Quan Zhou, Chao Sun
Summary: In this study, power spectra and structure functions (SFs) of the temperature and radial velocity fields in annular centrifugal Rayleigh-Benard convection (ACRBC) were analyzed. The results showed that both the energy spectrum and thermal spectrum exhibited Bolgiano and Obukhov-like scalings. These scalings became wider as the Rayleigh number increased.
Article
Mechanics
Yi-Bao Zhang, Heng-Dong Xi
Summary: This study investigates the effects of polymer additives on the energy cascade in turbulent von Karman swirling flow. The presence of polymers suppresses the energy injection, transfer, and dissipation rates. The dependence on both polymer concentration and Weissenberg number show similar effects on the energy cascade.
Article
Physics, Multidisciplinary
Hechuan Jiang, Dongpu Wang, Shuang Liu, Chao Sun
Summary: This study investigates the final state of turbulence when the driving parameter approaches infinity. By adopting a novel experimental setup, the existence of the ultimate regime is demonstrated with direct evidence. The findings greatly contribute to the understanding of flow dynamics in geophysical and astrophysical flows.
PHYSICAL REVIEW LETTERS
(2022)
Article
Mechanics
Hechuan Jiang, Dongpu Wang, Yu Cheng, Huageng Hao, Chao Sun
Summary: The influence of ratchets on inclined convection in a rectangular cell was studied through experiments and simulations. It was found that the arrangement of ratchets on the conducting plate determines the dynamics of the inclined convection. The present work provides insight into controlling inclined convection using asymmetric ratchet structures.
Article
Mechanics
Jun Zhong, Dongpu Wang, Chao Sun
Summary: This study investigates the coupling effect of buoyancy and shear using numerical simulations in an annular centrifugal Rayleigh-Benard convection system. The results show that shear can stabilize buoyancy-driven convection and enhance heat transfer. The study provides insights into the complex coupling mechanism between shear and buoyancy, which has implications for fundamental research and industrial applications.
JOURNAL OF FLUID MECHANICS
(2023)