Article
Mechanics
S. S. Gopalakrishnan, B. Knaepen, A. De Wit
Summary: The study investigates the convective finger structures formed by two solutions of different solutes in the gravity field, and analyses the nonlinear dynamics of these buoyancy-driven instabilities. Numerical simulations reveal the evolution of mixing length and the linear relationship between mixing velocity and dynamic density difference.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Hamid Emami-Meybodi, Fengyuan Zhang
Summary: This study focuses on the buoyancy-driven stability analysis in a three-dimensional inclined porous medium with a capillary transition zone. The results of linear stability analysis and numerical solutions show that the inclination angle plays a crucial role in the stability of the problem.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Antonio Barletta, Michele Celli, Stefano Lazzari, Pedro V. Brandao
Summary: This study reconsiders the classical Gill's stability problem in a vertical porous slab with impermeable and isothermal boundaries. Instead of studying a homogeneous slab, a three-layer slab with different thermal conductivities is examined. The results show that a flow instability may arise in the sandwiched porous slab when the Rayleigh number is sufficiently large. It is also demonstrated that this instability coincides with that predicted in a previous analysis for a homogeneous porous layer with permeable boundaries in the limiting case of highly permeable external layers compared to the core layer.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Stefan Gasow, Andrey V. Kuznetsov, Marc Avila, Yan Jin
Summary: This paper analyzes and extends recent pore-resolved direct numerical simulations, proposing a 'two-length-scale diffusion' model to accurately describe convection in porous media. The results show that macroscopic diffusion must be considered even when the Darcy number is small, and simulations using this model outperform those based on classic Darcy-Oberbeck-Boussinesq equations.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Marco De Paoli, Sergio Pirozzoli, Francesco Zonta, Alfredo Soldati
Summary: We conducted large-scale numerical simulations to study Rayleigh-Darcy convection in three-dimensional fluid-saturated porous media. The study revealed that at high Rayleigh-Darcy numbers, the flow is dominated by large columnar structures called megaplumes, which span the entire height of the domain. Near the boundaries, the flow is hierarchically organized with fine-scale structures forming larger-scale supercells. The results also showed a strong correlation between the flow structure in the core of the domain and at the boundaries. The study's findings are important for developing accurate models to predict the large- and fine-scale structure of Rayleigh-Darcy convection in geophysical processes.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Talib Dbouk, S. Amir Bahrani
Summary: For the first time, an Eulerian three-dimensional transient model was developed for thermal convection in immersed granular beds, successfully predicting local phenomena and introducing new concepts of critical Rayleigh number and critical temperature in the system.
INTERNATIONAL JOURNAL OF MULTIPHASE FLOW
(2021)
Article
Geochemistry & Geophysics
Nathan Sime, Jakob M. Maljaars, Cian R. Wilson, Peter E. van Keken
Summary: The study addresses numerical challenges in modeling the advection of chemical data in geodynamics using the hybrid discontinuous Galerkin (HDG) finite element method. It focuses on the necessity for mass conservation of chemical composition fields and the requirement for the velocity field to be pointwise divergence free. By comparing the system to other common FE formulations and chemical composition projections, the efficacy of the method is demonstrated. The importance of careful choices of appropriate discretization methods for geodynamics simulations is highlighted through a Rayleigh-Taylor instability benchmark reproduction.
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
(2021)
Article
Thermodynamics
Eren Colak, Ozgur Ekici, Hakan F. Oztop
Summary: This study investigates the lid-driven cavity problem under mixed convection conditions using Finite Volume Method (FVM). It is found that the Darcy number can control vortex formation and decrease in Darcy number can drastically increase the average Nusselt number. Heater orientation can be used to control heat transfer effectiveness, vortex shape and size, and can increase the average Nusselt number by 324%. Both heater location and orientation exhibit non-monotonic behavior for different flow parameters.
INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER
(2021)
Article
Thermodynamics
Junjie Liu, Xieeryazidan Aday, Guanlin Zhou, Zhenghe Ma
Summary: A new electrochemical machining model was established to study Marangoni and buoyancy-driven convection, with numerical simulations and experiments investigating the mechanisms of convection formation. Results showed that convection cells transitioned to an annular structure as processing voltage increased, forming both Marangoni and buoyancy convection in the processing region.
INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER
(2022)
Article
Mechanics
Thomas Le Reun, Duncan R. Hewitt
Summary: This study investigates convection in a horizontal layer consisting of a fluid-saturated porous bed overlain by an unconfined fluid layer. Under specific conditions, strong convection occurs in the system, and the heat flux and average thermal structure can be predicted based on previous results of convection in individual fluid or porous layers.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
B. M. Shankar, I. S. Shivakumara
Summary: The linear stability of thermal buoyant flow in a fluid-saturated vertical porous slab with weak and strong horizontal heterogeneities of the permeability is studied. Various heterogeneity models, including linear, quadratic, and exponential, are considered. The effectiveness of Gill's proof of linear stability is found to be ineffective and the possibilities of base flow becoming unstable due to heterogeneity in permeability are recognized. The study presents neutral stability curves and computes the critical Darcy-Rayleigh number for the onset of convective instability for different values of the variable permeability constant, highlighting the similarities and differences between different heterogeneity models on the stability of fluid flow.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Tingting Tang, Zhiyong Li, Shimin Yu, Jianhui Li, Peng Yu
Summary: In this study, the opposing-buoyancy mixed convection through and around a square array of heated circular cylinders was numerically investigated. The results revealed various interactions and bifurcation behaviors between the near-wake and far-wake vortexes under different parameter combinations.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Shuang Liu, Linfeng Jiang, Cheng Wang, Chao Sun
Summary: The numerical study investigated Rayleigh-Benard convection through random porous media, focusing on Lagrangian dynamics of fluid particles and heat transfer with varying porosities. The interaction between the porous medium and flow structures led to heterogeneous flow patterns, affecting the dynamics of fluid particles. This study also revealed enhanced heat transfer mechanisms in porous-media convection as porosity decreased.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Duncan R. Hewitt
Summary: This study investigates the effect of a series of thin, horizontal, low-permeability layers on convective motion in a two-dimensional porous medium. High-resolution numerical simulations and simple analytical models are used to explore the role of the Omega parameter and reveal a transition from predominantly diffusive to predominantly advective transfer for intermediate Omega values.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Jan G. G. Wissink, H. Herlina
Summary: Direct numerical simulations were performed to investigate the initial development of the Rayleigh-Benard-Marangoni (RBM) instability in a relatively deep domain. The simulations assumed a flat surface and modelled surface cooling with a constant heat flux. The small-scale dynamics of the flow and temperature fields near the surface were fully resolved using a non-uniform vertical grid distribution. The study provided a detailed investigation of the differences in physical mechanisms that drive the Rayleigh- and Marangoni-dominated instabilities and confirmed the enhancement of RBM instability by buoyancy and surface-temperature-gradient-driven Marangoni forces. The critical Marangoni and Rayleigh numbers obtained for the purely Marangoni- and purely Rayleigh-driven instabilities were in good agreement with the literature when using a relevant measure of the effective thermal boundary layer thickness as length scale.
JOURNAL OF FLUID MECHANICS
(2023)