Article
Mechanics
Changwen Liu, Yousheng Zhang, Zuoli Xiao
Summary: This paper presents a unified theory combining the classical potential-flow theory and a dual-source model to accurately predict the long-term developments in both growth rate and shape curvature of interfacial fingers in Rayleigh-Taylor and Richtmyer-Meshkov instabilities.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Changwen Liu, Hongzhi Wu-Wang, Yousheng Zhang, Zuoli Xiao
Summary: In this paper, the decoupled mechanisms of two effects are found to dominate the interface growth of the single-mode Rayleigh-Taylor instability (RTI) and Richtmyer-Meshkov instability (RMI) via Layzer's potential-flow model. These two effects, the inertial effect induced by the interfacial density gradient and acceleration and the frontal distortion effect stemming from interface shape evolution, can be approximated as a linearly decoupled analytical solution. The theoretical growth rates based on this decoupled solution agree well with numerical simulation results.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Alessandra Bonazzi, Birendra Jha, Felipe P. J. de Barros
Summary: The impact of viscosity and density contrasts on the transport dynamics of miscible flowing fluids in a porous medium under different initial conditions is investigated. The study shows that the initial shape of the source distribution and the intensity of the background flux have an influence on the temporal evolution of the spreading and mixing processes. It is found that the viscosity of the solute affects the rates of mixing, and the effects of horizontal viscous fingering dominate over gravitational fingering at higher background flux. The computational analysis also reveals a non-trivial relationship between mixing and the length of the plume's interface under fingering instabilities. Finally, the study demonstrates the interaction between a stratified permeability field and these instabilities, and how it affects the transport behavior of the plume.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Yun Chang, Alberto Scotti
Summary: This paper examines the early stage of radiatively driven convection and finds that perturbations grow exponentially over time, with the system characteristics determined by the Reynolds number.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Wenxuan Guo, Qiang Zhang, Dongdong He
Summary: Fluid interface instability caused by gravity or external acceleration, known as the Rayleigh-Taylor instability, is important in scientific research and industrial applications. Controlling this instability is challenging, and researchers have been exploring the method of applying electric fields to suppress it. The instability is characterized by the penetration of fingers at the interface, and the velocities at the finger tips are crucial for understanding the penetration speed. In this study, a nonlinear perturbation procedure is presented to determine the amplitude and velocity of fingers at a Rayleigh-Taylor unstable interface between two incompressible, inviscid, immiscible, and perfectly dielectric fluids in the presence of a horizontal electric field.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Meng Zhao, Zahra Niroobakhsh, John Lowengrub, Shuwang Li
Summary: In a Hele-Shaw cell, raising the upper plate perpendicularly at a prescribed speed creates complex, time-dependent interfacial patterns through Saffman-Taylor instability. The pattern formation process is sensitive to the lifting speed and not fully understood. Numerical results agree with experimental observations when the gap is increased at a constant rate, and nonlinear results show the existence of k-fold dominant, one-dimensional web-like networks with shape invariant gaps.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
S. J. Harris, N. R. McDonald
Summary: A two-dimensional model for the evolution of the fire line is formulated, considering three contributions to the fire line normal velocity. The conformal invariance of the coupled pair of partial differential equations is exploited to compute the evolution of radial and periodic fire lines numerically. A linear stability analysis shows that the stability of the fire line depends on the ratio of curvature to oxygen effects. For radial fires, the fire wind strength increases with the fire's effective radius, resulting in an increase in the Peclet number over time, making all fire lines eventually unstable. However, for periodic fire lines, the Peclet number remains constant, allowing for fire line stability.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
A. Mizev, E. A. Mosheva, D. A. Bratsun
Summary: In the experimental study, buoyancy-driven instabilities triggered by neutralization reactions were investigated, and a dimensionless parameter called reaction-induced buoyancy number was introduced to classify experimental observations and predict the development of two global scenarios based on the value of this parameter.
One scenario is mainly controlled by diffusion, resulting in weak convective motion, while the other leads to vigorous convection in the upper layer, causing the reaction front to move downwards quickly. A new parameter was shown to plot stability maps for predicting reaction-diffusion-convection processes in similar systems before experiments.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
D. A. Bratsun, A. Mizev, E. A. Mosheva
Summary: Theoretical study of buoyancy-driven chemoconvection induced by a neutralization reaction in a system of nitric acid and sodium hydroxide solutions reveals richer possible instabilities than previously thought. The formation of patterns depends on a single parameter, the reaction-induced buoyancy number, leading to insights necessary for a full understanding of the observed phenomena. The mathematical model developed includes reaction-diffusion-advection equations coupled with Navier-Stokes equations, with a focus on transient linear stability analysis and numerical simulations to examine system dynamics.
JOURNAL OF FLUID MECHANICS
(2021)
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)
Article
Mechanics
Y. Mezui, M. Obligado, A. Cartellier
Summary: This study revisits the hydrodynamics of bubble columns in the heterogeneous regime. By conducting experiments and analyzing data, the self-organization phenomenon in the heterogeneous regime and the applicability of velocity scaling under different conditions are confirmed. Furthermore, the importance of velocity scaling for coalescing media is discussed.
JOURNAL OF FLUID MECHANICS
(2022)
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
Min Chan Kim, Satyajit Pramanik, Vandita Sharma, Manoranjan Mishra
Summary: This study analyzes the impact of the A + B -> C chemical reaction on miscible viscous fingering in a radial source flow using linear stability theory and numerical simulations. The critical instability parameters RPhys,c and RChem,c decrease with decreasing Pe for large values of Da, exhibiting power-law behavior in Pe. In the asymptotic limit of infinitely large Pe, these parameters show a power-law dependence on Pe in both linear and nonlinear regimes, with R-Chem, R-c resembling Pe(-1/2) as Pe ->infinity.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
M. L'Estime, L. Duchemin, E. Reyssat, J. Bico
Summary: The adhesion of two surfaces depends on the propagation of an adhesion front. When both surfaces are coated with a viscous liquid, the front propagation may be unstable and lead to the formation of finger-like structures. The interfacial instability originates from the feeding of the front from the surrounding thin film.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Katarzyna N. Kowal
Summary: The study demonstrates a novel instability in unconfined viscous bands or free-surface flows, known as viscous banding instabilities. Unlike the Saffman-Taylor instabilities in porous media, these instabilities are driven by a viscosity contrast and do not require confinement like in a Hele-Shaw cell. The main difference lies in the driving mechanisms, with Saffman-Taylor instabilities driven by dynamic pressure gradients and viscous banding instabilities driven by hydrostatic pressure gradients related to slope discontinuities.
JOURNAL OF FLUID MECHANICS
(2021)