Article
Mechanics
Philipp Reiter, Xuan Zhang, Rodion Stepanov, Olga Shishkina
Summary: This study investigates the impact of travelling thermal waves on the formation of global flow structures in 2-D and 3-D convective systems. Results show that in diffusion dominated regimes, zonal flows are driven purely by Reynolds stresses and always travel retrograde, while in convection dominated regimes, mean flow advection caused by tilted convection cells becomes dominant, leading to prograde directed mean zonal flows. The findings are validated through direct numerical simulations and provide further evidence for the relevance of the results for geophysical and astrophysical systems.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Xuan Zhang, Robert E. Ecke, Olga Shishkina
Summary: In rapidly rotating turbulent Rayleigh-Benard convection with a small Prandtl number fluid in slender cylindrical containers, a boundary zonal flow (BZF) is found to develop near the sidewall, carrying a disproportionate amount of heat transport for Pr < 1 but decreasing abruptly for larger Pr. The BZF is robust and appears in containers of different aspect ratios and over a broad range of Pr and Ra values.
JOURNAL OF FLUID MECHANICS
(2021)
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
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
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
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
Scott T. Salesky
Summary: Wall-bounded turbulent flows with unstable thermal stratification show a zonal arrangement with uniform momentum zones (UMZs) separated by elevated interfacial shear layers. This study investigates the statistical properties of UMZs and uniform temperature zones (UTZs) in unstably stratified turbulent channel flow. Results show a connection between UMZ properties and scaling predictions from Monin-Obukhov similarity theory, as well as a similar relationship between UTZ properties and surface-layer scaling of the mean temperature gradient. The instantaneous structures of UMZs and UTZs are found to be related to the well-mixed velocity and temperature profiles in the convective mixed layer.
JOURNAL OF FLUID MECHANICS
(2023)
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
Naoki Hori, Chong Shen Ng, Detlef Lohse, Roberto Verzicco
Summary: This study investigates the behavior of immiscible and incompressible liquid-liquid flows in a Taylor-Couette geometry using direct numerical simulations coupled with the volume-of-fluid method and a continuum surface force model. The interactions between the interface and the Taylor vortices are studied by varying the secondary-phase volume fraction and the system Weber number. The results reveal two different flow regimes depending on the Weber number, namely an advection-dominated regime and an interface-dominated regime.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Rui Yang, Christopher J. Howland, Hao-Ran Liu, Roberto Verzicco, Detlef Lohse
Summary: This study numerically investigates the melting process of a solid layer heated from below and finds that thermal convection leads to increased roughness of the interface, which is coupled to the flow topology. The structure of the interface coincides with the regions of rising hot plumes and descending cold plumes, and the roughness amplitude scales with the mean height of the liquid layer.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Physics, Fluids & Plasmas
Christopher J. Howland, Roberto Verzicco, Detlef Lohse
Summary: Motivated by ice ablation in salt water, this study investigates the heat and salt fluxes in two-scalar vertical convection using three-dimensional direct numerical simulations. The salinity field drives the convection while heat is transported as passive scalar. The diffusivity ratio of heat and salt affects the scalar fluxes, with heat transport determined by a turbulent Prandtl number of Prt approximate to 1 and double-diffusive effects being negligible.
PHYSICAL REVIEW FLUIDS
(2023)
Article
Computer Science, Interdisciplinary Applications
Youssef Saade, Detlef Lohse, Daniel Fuster
Summary: We extend the all-Mach solver proposed by Fuster and Popinet (2018) [1] to account for heat diffusion between two compressible phases. By solving a coupled system of equations for pressure and temperature, our code improves the robustness and accuracy of the solver compared to classical explicit discretization schemes. Several test cases are used to validate the implementation, including comparisons with spectral methods and analytical solutions. The code is also applied to the study of sonoluminescent bubbles, Rayleigh collapse, and bubble collapse near a rigid boundary, demonstrating the importance of thermal effects in these phenomena.
JOURNAL OF COMPUTATIONAL PHYSICS
(2023)
Editorial Material
Mechanics
Richard J. A. M. Stevens
Summary: Kirby et al. adapted the two-scale momentum theory to large finite-sized wind farms and demonstrated good agreement with simulations. They introduced the concepts of farm-scale and turbine-scale losses, providing a novel way to analyze wind farm performance. Layout optimizations have limited potential, and increasing energy entrainment into the wind farm should be the focus of optimization strategies. This work offers an exciting roadmap for analyzing the efficiency of large wind farms.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Pierre Chantelot, Detlef Lohse
Summary: Gas film and nonlinear advection are two physical mechanisms affecting the rebounding of impacting drops. We reveal the dominance of the nonlinear advection regime through impacts on superheated surfaces. By measuring the gas film thickness under impacting drops, we provide evidence for the transition from the surface tension to the nonlinear inertia dominated regime.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Vatsal Sanjay, Pierre Chantelot, Detlef Lohse
Summary: Using numerical simulations, we investigate how viscous stresses and gravity inhibit drop rebound by opposing capillarity. We find that the initial spreading stage can be decoupled from the later retraction and take-off, and propose a criterion for the transition from bouncing to non-bouncing regime. The criterion is in excellent agreement with the numerical results. We also elucidate the mechanisms of bouncing inhibition in the heavy and viscous drop limiting regimes.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Physics, Fluids & Plasmas
Yuki Wakata, Ning Zhu, Xiaoliang Chen, Sijia Lyu, Detlef Lohse, Xing Chao, Chao Sun
Summary: In this study, we investigate the Leidenfrost temperature for hot solid substrates with different thermal diffusivities and surface roughnesses. A phenomenological model is developed based on experimental data, which considers the thermal diffusivity of the solid substrate and establishes the relationship between surface roughness and vapor film thickness. The generality of this model is supported by experimental data for various liquids and solid substrates, providing a theoretical prediction of the Leidenfrost temperature and a comprehensive understanding of the Leidenfrost effect.
PHYSICAL REVIEW FLUIDS
(2023)
Article
Computer Science, Interdisciplinary Applications
Francesco Viola, Valentina Meschini, Roberto Verzicco
Summary: Fluid-structure-electrophysiology interaction (FSEI) is used to study the effects of aortic valve stenosis on hemodynamics, which is caused by the stiffening of valve leaflets and reduces the pumping efficiency of the heart. By gradually increasing the severity of the disease in a high-fidelity model, we observed an increase in transvalvular pressure drop and peak systolic jet velocity, as well as a reduction in cardiac ejection fraction. The stenotic aortic valve also significantly alters wall shear stresses and their distribution, potentially leading to remodeling of the ventricular myocardium. The numerical results of the multi-physics model are consistent with clinical experience, supporting the use of computational engineering in medical diagnostics.
COMPUTERS & FLUIDS
(2023)
Article
Mechanics
Nikolas O. Aksamit, Robert Hartmann, Detlef Lohse, George Haller
Summary: Mathematical developments in the theory of objective coherent structures have improved our understanding of the material organization of complex fluid flows. However, there is limited investigation into these objectively defined transport barriers in 3-D unsteady flows with complicated spatiotemporal dynamics. Our study utilizes simulations to uncover the interplay between different types of barriers in turbulent rotating Rayleigh-Bénard convection.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Jochem G. Meijer, Yanshen Li, Christian Diddens, Detlef Lohse
Summary: When an immiscible oil drop is immersed in a stably stratified ethanol-water mixture, it undergoes a transition from levitating to bouncing due to the oscillatory instability of the Marangoni flow on the drop's surface. The bouncing characteristics of the drop, such as jumping height and rising and sinking time, are studied in relation to the control parameters of drop radius, stratification strength, and drop viscosity. Experimental observations are backed by a simplified dynamical analysis and numerical simulations to verify the drag coefficients.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
F. Viola, R. Verzicco
Summary: This study investigates the effect of gravity on the harmonic modes of static droplets and solves axisymmetric and non-axisymmetric modes using an effective boundary element method. The study also revises a debated capillary instability.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Rui Yang, Christopher J. Howland, Hao-Ran Liu, Roberto Verzicco, Detlef Lohse
Summary: The presence of salt affects the melt rate and shape evolution of ice in seawater. Numerical simulations and experiments are used to study ice melting in saline water. The melt rate of ice decreases and then increases with increasing salt concentration due to the competition between salinity-driven and temperature-driven buoyancy. A theoretical model based on force balance predicts the minimal salt concentration for ice melt rate, consistent with the data. Interplay between phase transitions and double-diffusive convective flows is revealed.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Physics, Fluids & Plasmas
Pallav Kant, Cesar Pairetti, Youssef Saade, Stephane Popinet, Stephane Zaleski, Detlef Lohse
Summary: We use experiments and numerical computations to study the fluid mechanical processes involved in the generation of bioaerosols during forceful respiratory maneuvers like coughing or sneezing. By performing analogous experiments on a cough machine, we observe the disintegration of a thin liquid film into small droplets and identify that aerosol generation is mediated by the formation of inflated baglike structures. The breakup of these bags is triggered by retracting holes on the surface, and the dynamics and stability of the liquid rims bounding these holes play a key role in the cascade from inflated bags to droplets. The viscosity of the fluid also affects the fragmentation process, with more viscous films producing smaller droplets.
PHYSICAL REVIEW FLUIDS
(2023)