Browsing by Author "Miranda, Jose A."

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Controlling radial fingering patterns in miscible confined flows
(2010-11-11)
Chen, Ching-Yao
;
Huang, C. -W.
;
Wang, L. -C.
;
Miranda, Jose A.
;
機械工程學系
Injection-driven immiscible flow in radial Hele-Shaw cells results in highly ramified patterns if the injection rate is constant in time. Likewise, time-dependent gap immiscible flow in lifting Hele-Shaw cells leads to intricate morphologies if the cell's gap width grows exponentially with time. Recent studies show that the rising of these complex fingered structures can be controlled by properly adjusting the injection rate, and the time-dependent gap width. We investigate the effectiveness of these control strategies assuming that the fluids involved are miscible. Despite the absence of surface tension effects, intensive numerical simulations support the stabilizing role of these controlling protocols. Splitting, merging and competition of fingers are all inhibited. The sensitivity of the system to changes in the initial conditions and Peclet numbers is also discussed.
Controlling radial fingering patterns in miscible confined flows
(2010-11-11)
Chen, Ching-Yao
;
Huang, C. -W.
;
Wang, L. -C.
;
Miranda, Jose A.
;
機械工程學系
Injection-driven immiscible flow in radial Hele-Shaw cells results in highly ramified patterns if the injection rate is constant in time. Likewise, time-dependent gap immiscible flow in lifting Hele-Shaw cells leads to intricate morphologies if the cell's gap width grows exponentially with time. Recent studies show that the rising of these complex fingered structures can be controlled by properly adjusting the injection rate, and the time-dependent gap width. We investigate the effectiveness of these control strategies assuming that the fluids involved are miscible. Despite the absence of surface tension effects, intensive numerical simulations support the stabilizing role of these controlling protocols. Splitting, merging and competition of fingers are all inhibited. The sensitivity of the system to changes in the initial conditions and Peclet numbers is also discussed.
Diffuse-interface approach to rotating Hele-Shaw flows
(2011-10-05)
Chen, Ching-Yao
;
Huang, Yu-Sheng
;
Miranda, Jose A.
;
機械工程學系
;
Department of Mechanical Engineering
When two fluids of different densities move in a rotating Hele-Shaw cell, the interface between them becomes centrifugally unstable and deforms. Depending on the viscosity contrast of the system, distinct types of complex patterns arise at the fluid-fluid boundary. Deformations can also induce the emergence of interfacial singularities and topological changes such as droplet pinch-off and self-intersection. We present numerical simulations based on a diffuse-interface model for this particular two-phase displacement that capture a variety of pattern-forming behaviors. This is implemented by employing a Boussinesq Hele-Shaw-Cahn-Hilliard approach, considering the whole range of possible values for the viscosity contrast, and by including inertial effects due to the Coriolis force. The role played by these two physical contributions on the development of interface singularities is illustrated and discussed.
Enhanced mixing via alternating injection in radial Hele-Shaw flows
(2015-10-07)
Chen, Ching-Yao
;
Huang, Yi-Cheng
;
Huang, Yu-Sheng
;
Miranda, Jose A.
;
機械工程學系
Mixing at low Reynolds numbers, especially in the framework of confined flows occurring in Hele-Shaw cells, porous media, and microfluidic devices, has attracted considerable attention lately. Under such circumstances, enhanced mixing is limited due to the lack of turbulence, and absence of sizable inertial effects. Recent studies, performed in rectangular Hele-Shaw cells, have demonstrated that the combined action of viscous fluid fingering and alternating injection can dramatically improve mixing efficiency. In this work, we revisit this important fluid mechanical problem, and analyze it in the context of radial Hele-Shaw flows. The development of radial fingering instabilities under alternating injection conditions is investigated by intensive numerical simulations. We focus on the impact of the relevant physical parameters of the problem (Peclet number Pe, viscosity contrast A, and injection time interval Delta t) on fluid mixing performance.
EXPERIMENTAL STUDY OF A HYBRID FERROHYDRODYNAMIC INSTABILITY IN MISCIBLE FERROFLUIDS: DROPLET SIZE EFFECTS
(2009-01-01)
Chen, Ching-Yao
;
Tsai, W. -K.
;
Miranda, Jose A.
;
機械工程學系
;
Department of Mechanical Engineering
Recently, we have performed a ferrofluid experiment that revealed the existence of a hybrid ferrohydrodynamic situation in which a three-dimensional Collapsing Rosensweig peak and effectively-two-dimensional labyrinthine structures occur simultaneously (C.-Y. Chen et al. Phys. Rev. E., vol. 77 (2008) 056306.) This has been done by immersing a ferrofluid droplet in a thin layer of a miscible nonmagnetic fluid, under the action of a vertically applied magnetic field. We extend the investigation of this new system focusing on the effects produced by ferrofluid droplets of different sizes. It, is found that; larger droplets result in a more promient manifestation of both interfacial instabilities. Moreover, the observations of the labyrinthine fingering patterns are extended into very late stages, where the decaying ferrofluid peak has been completely reimmersed into the surrounding nowmagnetic fluid.
Hybrid ferrohydrodynamic instability: Coexisting peak and labyrinthine patterns
(2008-05-01)
Chen, Ching-Yao
;
Tsai, W. -K.
;
Miranda, Jose A.
;
機械工程學系
;
Department of Mechanical Engineering
We present an experimental study of a different pattern-forming instability occurring when a ferrofluid droplet is immersed in a thin layer of a nonmagnetic fluid, and subjected to a uniform perpendicular magnetic field. The formation of intriguing interfacial structures is observed, and the development of a hybrid-type ferrohydrodynamic instability is verified, where peak and labyrinthine ferrofluid patterns coexist and share a coupled dynamic evolution. Based on our experimental findings we have identified the occurrence of three well defined regimes for the evolution of the miscible Rosensweig peak in which it first grows rapidly, and then gradually decays, to ultimately reimmerse into the surrounding nonmagnetic solvent layer. This unique scenario for the rise and fall of the Rosensweig peak implies the simultaneous emergence of peculiar labyrinthine structures induced by an outward radial flow within the thin nonmagnetic layer. A variety of possible morphologies is revealed (labyrinth, broken tentaclelike fingers, etc.), which result from the interplay between magnetic, diffusive, and convective effects. These free surface flow labyrinthine structures are contrasted to alternative interfacial designs obtained when the experimental system is spatially confined.
Magnetically induced spreading and pattern selection in thin ferrofluid drops
(2010-11-17)
Chen, Ching-Yao
;
Wu, W. -L.
;
Miranda, Jose A.
;
機械工程學系
;
Department of Mechanical Engineering
We report an experimental study of a fingering pattern formation which occurs during the spreading of an immiscible thin ferrofluid drop subjected to a radial magnetic field. Our results indicate that this ferrohydro-dynamic system works as a magnetic analog of conventional spin coating, where centrifugal driving is replaced with a magnetic body force induced by the radial applied field. In this context, a magnetically tunable pattern selection mechanism is proposed in which the shape and number of the arising fingered structures can be properly controlled.
Magnetically induced spreading and pattern selection in thin ferrofluid drops
(2010-11-17)
Chen, Ching-Yao
;
Wu, W. -L.
;
Miranda, Jose A.
;
機械工程學系
;
Department of Mechanical Engineering
We report an experimental study of a fingering pattern formation which occurs during the spreading of an immiscible thin ferrofluid drop subjected to a radial magnetic field. Our results indicate that this ferrohydro-dynamic system works as a magnetic analog of conventional spin coating, where centrifugal driving is replaced with a magnetic body force induced by the radial applied field. In this context, a magnetically tunable pattern selection mechanism is proposed in which the shape and number of the arising fingered structures can be properly controlled.
Miscible ferrofluid patterns in a radial magnetic field
(2009-07-01)
Chen, Ching-Yao
;
Yang, Y. -S.
;
Miranda, Jose A.
;
機械工程學系
;
Department of Mechanical Engineering
Pattern formation in a miscible ferrofluid system is experimentally investigated. The experiment is performed by immersing a thin ferrofluid droplet in a cylindrical container, overfilling it with a nonmagnetic miscible fluid, and applying an in-plane radial magnetic field. Visually striking patterns are obtained whose morphologies change from circular at zero field to complex starburstlike structures at finite field. The evolution of miscible ferrofluid droplets of various initial diameters subjected to different magnetic-field strengths is considered. Proper rescaling of the experimental data indicates that the time evolution of the droplets' area increments obeys a universal 4/3 power-law behavior at long times.
Radial Hele-Shaw flow with suction: Fully nonlinear pattern formation
(2014-05-09)
Chen, Ching-Yao
;
Huang, Yu-Sheng
;
Miranda, Jose A.
;
機械工程學系
;
Department of Mechanical Engineering
We study the development of intricate, fully nonlinear immiscible interfacial patterns in the suction-driven radial Hele-Shaw problem. The complex-shaped, contracting fluid-fluid interface arises when an initially circular blob of more viscous fluid, surrounded by less viscous one, is drawn into an eccentric point sink. We present sophisticated numerical simulations, based on a diffuse interface model, that capture the most prominent interfacial features revealed by existing experimental studies of the problem. The response of the system to changes in the capillary number is investigated, accurately revealing the occurrence of finger competition phenomena, and correctly describing the velocity behavior of both inward-and outward-pointing fingers. For the large-capillary-number regime, a set of complex interfacial features (finger merging, shielding, and pinch-off) whose experimental realization is still not available, are predicted.
Radial viscous fingering in miscible Hele-Shaw flows: A numerical study
(2008-07-01)
Chen, Ching-Yao
;
Huang, C. -W.
;
Gadelha, Hermes
;
Miranda, Jose A.
;
機械工程學系
A modified version of the usual viscous fingering problem in a radial Hele-Shaw cell with immiscible fluids is studied by intensive numerical simulations. We consider the situation in which the fluids involved are miscible, so that the diffusing interface separating them can be driven unstable through the injection or suction of the inner fluid. The system is allowed to rotate in such a way that centrifugal and Coriolis forces come into play, imposing important changes on the morphology of the arising patterns. In order to bridge from miscible to immiscible pattern forming structures, we add the surface tensionlike effects due to Korteweg stresses. Our numerical experiments reveal a variety of interesting fingering behaviors, which depend on the interplay between injection (or suction), diffusive, rotational, and Korteweg stress effects. Whenever possible the features of the simulated miscible fronts are contrasted to existing experiments and other theoretical or numerical studies, usually resulting in close agreements. A number of additional complex morphologies, whose experimental realization is still not available, are predicted and discussed.
Rotationally induced fingering patterns in a two-dimensional heterogeneous porous medium
(2016-11-04)
Chen, Ching-Yao
;
Lin, Ting-Shiang
;
Miranda, Jose A.
;
機械工程學系
;
Department of Mechanical Engineering
Rotating fluid flows under two-dimensional homogeneous porous media conditions (or in a rotating Hele-Shaw cell) reveal the development of complex interfacial fingering patterns. These pattern-forming structures are characterized by the occurrence of finger competition events, finger pinch-off episodes, as well as by the production of satellite droplets. In this work, we use intensive numerical simulations to investigate how these fully nonlinear pattern growth phenomena are altered by the presence of permeability heterogeneities in the rotating porous medium. This is done by employing a diffuse-interface Darcy-Cahn-Hilliard description of the problem and considering a permeability field presenting a log-Gaussian distribution, characterized by a variance s and a correlation length l. We study how the heterogeneity measures s and l couple to the governing hydrodynamic dimensionless parameters of the problem and introduce important changes on the pattern formation dynamics of the system.