Formation Of Flow Patterns Research Articles

Pattern formation in 2D traffic flows

We review numerical and analytical results that have been obtained for a general model of intersecting flows of two types of particles propagating towards east ($\varepsilon $) and north ($\mathcal{N} $) on a bidimensional $M \times M$ square lattice. The behaviour of this model can also be reproduced by a system of mean field equations. The low density behaviour of both models is studied, with a focus on pattern formation. Using periodic boundary conditions, particles self-organize into a pattern of alternating diagonal stripes, which corresponds to an instability in the mean-field equations. With open boundary conditions, translational symmetry is broken. One then observes an asymmetry between the organization of the two types of particles, leading to tilted diagonals whose angle of inclination differs from $45^\circ$, both for the particle system and the equations. The angle of inclination of the stripes is measured using two different numerical methods. Finally, simplified theoretical arguments based on a particular mode of propagation give a quantitative estimate for the angle of the stripes. A complementary understanding of the phenomenon in terms of effective interactions between particles is presented.

Confinement effects on electrohydrodynamics of two-dimensional miscible liquid drops

The effect of domain confinement on the electrohydrodynamics of a two-dimensional miscible drop is investigated analytically, as a prototypical problem to explore confinement effect in two applications; namely, continuous flow electrophoresis and pattern formation in suspension of inhomogeneous colloidal dispersions. It is shown that the domain confinement may strengthen or weaken the electric field and leads to weakening of the flow field and change of the flow structure. A characteristic function is found to determine the sense of drop elongation and it is shown that below a critical domain size, the necessary condition for elongation in the direction normal to the field will be opposite to that for an unbounded domain.

Comparison of flow patterns of dual rushton and CD-6 impellers

The flow patterns (parallel, merging and diverging) of dual CD-6 impeller has been modeled using computational fluid dynamics simulation in FLUENT software compared with dual Rushton impeller. Simulated results have been verified with experimental observations on Rushton impeller. Comparison of simulated and experimental results of Rushton impeller has been observed similar flow patterns, whereas CD-6 impeller exhibits different flow pattern from the Rushton impeller in merging flow pattern. Analysis has shown that formation of flow patterns of Rushton impeller and CD-6 impeller is different in the case of merging flow pattern.

How the Propagation of Heat-Flux Modulations TriggersE×BFlow Pattern Formation

We propose a novel mechanism to describe E×B flow pattern formation based upon the dynamics of propagation of heat-flux modulations. The E × B flows of interest are staircases, which are quasiregular patterns of strong, localized shear layers and profile corrugations interspersed between regions of avalanching. An analogy of staircase formation to jam formation in traffic flow is used to develop an extended model of heat avalanche dynamics. The extension includes a flux response time, during which the instantaneous heat flux relaxes to the mean heat flux, determined by symmetry constraints. The response time introduced here is the counterpart of the drivers' response time in traffic, during which drivers adjust their speed to match the background traffic flow. The finite response time causes the growth of mesoscale temperature perturbations, which evolve to form profile corrugations. The length scale associated with the maximum growth rate scales as Δ(2) ~ (v(thi)/λT(i))ρ(i)sqrt[χ(neo)τ], where λT(i) is a typical heat pulse speed, χ(neo) is the neoclassical thermal diffusivity, and τ is the response time of the heat flux. The connection between the scale length Δ(2) and the staircase interstep scale is discussed.

Application of X-ray radioscopic methods for characterization of two-phase phenomena and solidification processes in metallic melts

X-ray attenuation techniques are an important diagnostic tool for investigating liquid metal two-phase flows or solidification studies in metallic alloys. X-ray visualization enables a general, intuitive understanding of flow phenomena or pattern formation in opaque liquid metal systems. Real-time and in-situ observations of the density distribution within thin solidifying samples achieve a spatial resolution of a few microns and contribute significantly to an improved understanding of dendritic growth processes. Moreover, X-ray radioscopy is a useful tool for a non-invasive, in-situ visualization and characterization of gas bubbles in nontransparent melts or for observations of the formation of metal foams. In this paper we consider three different fields of application which are under intensive investigation at HZDR and TUD: the bottom-up solidification of Ga-In alloys under the influence of buoyancy-driven and electromagnetically driven convection, the injection of Ar gas into liquid GaInSn, the study of Al foams with respect to foam formation and the characterization of their internal structure.

CFD Analysis of Spatial Distribution of Various Parameters in Downdraft Gasifier

Gasification converts carbonaceous pulverized fuels into synthesis gas, a mixture of CO and H2 that is a raw material for chemicals as well as a fuel for producing electricity. Gasification produces a much higher concentration of carbon dioxide than direct combustion of coal in air. In view of these, gasification energy combined with Computational Fluid Dynamics (CFD) software has been described in some detail in the following study. The aspect of gasification processes have been investigated for down-draft gasifier using simulation in FLUENT software. The formation of flow pattern, temperature, turbulence and product gas composition were investigated. Some of the results are compared with the results available from the literature.

CFD Simulation of Flow Patterns in Dual Impeller Stirred Tank

The hydrodynamics of fluid flow inside the stirred tanks are characterized by the flow patterns, which differ with the types of impeller (Rushton, CD-6), number of impellers (more than one) and their clear off distances (S1, S2, S3). Due to the wide application of stirred tanks in process industries, it is required to understand the hydrodynamics of fluid flow for its optimum design. Literature suggests that there exist three most significant flow patterns as parallel, merging and diverging flow in dual impeller–stirred tank at specific impeller clear off distances. In this study, these types of flow patterns have been analysed using computational fluid dynamics (CFD) techniques with multiple reference frame (MRF) impeller model in dual impeller (same diameter) of Rushton and CD-6 impeller since these two impellers act differently in the performance of stirred tanks. From the comparison of Rushton and CD-6 impeller in terms of mean flow and turbulent kinetic energy, it has been observed that there is no distinct difference in the formation of flow patterns, but apparently witnessed strong magnitude in the case of CD-6 impeller.

Limited penetrable visibility graph from two-phase flow for investigating flow pattern dynamics

We optimize and design a new half-ring conductance sensor for measuring two-phase flow in a small diameter pipe. Based on the experimental signals measured from the designed sensor, we using the limited penetrable visibility graph we proposed construct complex networks for different flow patterns. Through analyzing the constructed networks, we find that the joint distribution of the allometric scaling exponent and the average degree of the network allows distinguishing different gas-liquid flow patterns in a small diameter pipe. The curve peak of the degree distribution allows uncovering the detailed features of the flow structure associated with the size of gas bubbles, the average degree of the network can reflect the macroscopic property of the flow behavior, The allometric scaling exponent is very sensitive to the complexity of fluid dynamics and allows characterizing the dynamic behaviors in the evolution of different flow patterns. In this regard, limited penetrable visibility graph analysis of fluid signals can provide a new perspective and a novel tool for uncovering the dynamical mechanisms governing the formation and evolution of different flow patterns.

Eulerian–Lagrangian method for three-dimensional simulation of fluidized bed coal gasification

A comprehensive three-dimensional numerical model has been developed to simulate the coal gasification in a fluidized bed gasifier. The methodology is based on the multiphase particle-in-cell (MP-PIC) model, which uses an Eulerian method for fluid phase and a discrete particle method for particle phase. Dense particulate flow, mass and heat transfer, homogeneous and heterogeneous chemistry between phases and within the fluid mixture are considered. The dynamics of the particle phase is calculated by solving a transport equation for the particle distribution function (PDF) f. Particle collisions and chemical reactions are solved on a grid cell with particle properties mapped from discrete particles to the grid. Solid mass consumed or produced in reactions changes the size of particles. Simulations were carried out in a coal gasifier with a height of 2.0m and a diameter of 0.22m at atmosphere. The calculated product gas compositions compare well with the experimental data. The formation of flow patterns, profiles of particle species and gas compositions, distributions of reaction rates and consumption of carbon mass were investigated under different operating conditions.

Passive control of flow structures around a circular cylinder by using screen

The results of PIV measurements are presented in this paper for the water flow downstream of a circular cylinder surrounded with a screen (meshed outer control element) which had a streamlined shape. The diameter of cylinder, D was 50mm and the Reynolds number based on the cylinder diameter was 5200. The characteristic length of the control element, L was tested for different cases so that the values of L/D were 2, 2.4, 2.8 and 3.2 in the experiments. It was noted that a forced reattachment of the shear layers separated from the cylinder was achieved by setting up the screen around the cylinder. As a consequence, the formation of vortical flow pattern was suppressed and turbulence statistics of the flow such as the intensity of turbulence, Reynolds shear stress, and turbulent kinetic energy were drastically diminished in comparison to the bare cylinder case. It was also found that the variable parameter of L/D did not dominantly influence the characteristics of the distribution of turbulence statistics along streamwise and transverse directions, however, the turbulence level decreased slightly for a smaller case of L/D.

The Dynamics of Visual Experience, an EEG Study of Subjective Pattern Formation

BackgroundSince the origin of psychological science a number of studies have reported visual pattern formation in the absence of either physiological stimulation or direct visual-spatial references. Subjective patterns range from simple phosphenes to complex patterns but are highly specific and reported reliably across studies.Methodology/Principal FindingsUsing independent-component analysis (ICA) we report a reduction in amplitude variance consistent with subjective-pattern formation in ventral posterior areas of the electroencephalogram (EEG). The EEG exhibits significantly increased power at delta/theta and gamma-frequencies (point and circle patterns) or a series of high-frequency harmonics of a delta oscillation (spiral patterns).Conclusions/SignificanceSubjective-pattern formation may be described in a way entirely consistent with identical pattern formation in fluids or granular flows. In this manner, we propose subjective-pattern structure to be represented within a spatio-temporal lattice of harmonic oscillations which bind topographically organized visual-neuronal assemblies by virtue of low frequency modulation.

Stimulation of vigorous rotational flows and novel flow patterns using triaxial magnetic fields

We have discovered that new flow patterns can be created by applying a dc field to the ac biaxial fields that are used to induce isothermal magnetic advection (IMA). IMA is a recently discovered fluid flow phenomenon that occurs in suspensions of magnetic platelets subjected to particular time-dependent, uniform, biaxial magnetic fields. IMA is characterized by the formation of emergent flow patterns called advection lattices. We find that a dc field can disrupt the antiparallel flow symmetry of the advection lattice and give rise to qualitatively new flow patterns, including vigorous rotational flows and a highly regular diamond lattice. The rotational flows are very robust and may have applications to heat transfer. The diamond lattice is an intriguing and challenging example of emergent dynamics. Both of these effects occur when the dc field is applied orthogonal to the plane of the biaxial field.

Abnormal Left Ventricular Vortex Flow Patterns in Association With Left Ventricular Apical Thrombus Formation in Patients With Anterior Myocardial Infarction

The current study was designed to investigate the correlation between the left ventricular (LV) vortex flow pattern and LV apical thrombus formation in patients with acute anterior wall myocardial infarction (MI). Fifty-seven patients with acute anterior wall MI were enrolled in this study. Eighteen patients with apical thrombus (thrombus group) and 39 patients without apical thrombus (non-thrombus group) underwent 2-dimensional contrast echocardiography (CE). Morphology and pulsatility parameters of the LV vortex were measured using Omega flow(®) and compared between the 2 groups. In the thrombus group, the vortex was located more centrally and did not extend to the apex. In the thrombus group, quantitative vortex parameters of vortex depth (0.409±0.101 vs. 0.505±0.092, respectively; P=0.002) and relative strength (1.574±0.310 vs. 1.808±0.376, respectively, P=0.034) were significantly lower than the non-thrombus group. Following multivariate analysis, the vortex depth below 0.45 remained a significant independent parameter for formation of the LV apical thrombus (odds ratio 9.714, 95% confidence interval 1.674-56.381, P=0.011). These findings suggest that the location and pulsatility power of the LV vortex are strongly associated with the LV thrombus formation in patients with anterior MI. Therefore, LV vortex flow analysis using CE can be clinically useful for characterizing and quantifying the risk of LV apical thrombus in patients with anterior MI.

Liquid–Liquid Flow in a Capillary Microreactor: Hydrodynamic Flow Patterns and Extraction Performance

The capillary microreactor, with four stable operating flow patterns and a throughput range from grams per hour to kilograms per hour, presents an attractive alternative to chip-based and microstructured reactors for laboratory- and pilot-scale applications. In this article, results for the extraction of 2-butanol from toluene under different flow patterns in a water/toluene flow in long capillary microreactors are presented. The effects of the capillary length (0.4–2.2 m), flow rate (0.1–12 mL/min), and aqueous-to-organic volumetric flow ratio (0.25–9) on the slug, bubbly, parallel, and annular flow hydrodynamics were investigated. Weber-number-dependent flow maps were composed for capillary lengths of 0.4 and 2 m that were used to interpret the flow pattern formation in terms of surface tension and inertia forces. When the capillary length was decreased from 2 to 0.4 m, a transition from annular to parallel flow was observed. The capillary length had little influence on slug and bubbly flows. The flow p...

Complexity, segregation, and pattern formation in rotating-drum flows

Rotating-drum flows span a variety of research areas, ranging from physics of granular matter through hydrodynamics of suspensions to pure liquid coating flows. Recent years have seen an intensified scientific activity associated with this unique geometrical configuration, which has contributed to our understanding of related subjects such as avalanches in granules and segregation in suspensions. The existing literature related to rotating-drum flows is reviewed, highlighting similarities and differences between the various flow realizations. Scaling laws expressing the importance of different mechanisms underlying the observed phenomena have been focused on. An emphasis is placed on pattern formation phenomena. Rotating-drum flows exhibit stationary patterns as well as traveling and oscillating patterns; they exhibit reversible transitions as well as hysteresis. Apart from the predominant cylindrical configuration, this review covers recent work done with tumblers having other geometries, such as the sphere and the Hele-Shaw cell.

Noise Properties of Rectifying Nanopores

Ion currents through three types of rectifying nanoporous structures are studied and compared: conically shaped polymer nanopores, glass nanopipettes, and silicon nitride nanopores. Time signals of ion currents are analyzed by the power spectrum. We focus on the low-frequency range where the power spectrum magnitude scales with frequency, f, as 1/f. Glass nanopipettes and polymer nanopores exhibit nonequilibrium 1/f noise; thus, the normalized power spectrum depends on the voltage polarity and magnitude. In contrast, 1/f noise in rectifying silicon nitride nanopores is of equilibrium character. Various mechanisms underlying the voltage-dependent 1/f noise are explored and discussed, including intrinsic pore wall dynamics and formation of vortices and nonlinear flow patterns in the pore. Experimental data are supported by modeling of ion currents based on the coupled Poisson−Nernst−Planck and Navier−Stokes equations. We conclude that the voltage-dependent 1/f noise observed in polymer and glass asymmetric nanopores might result from high and asymmetric electric fields, inducing secondary effects in the pore, such as enhanced water dissociation.

Three dimensional numerical simulation of gas–liquid two-phase flow patterns in a polymer–electrolyte membrane fuel cells gas flow channel

Water management in polymer–electrolyte membrane fuel cells (PEMFCs) has a major impact on fuel cell performance and durability. To investigate the two-phase flow patterns in PEMFC gas flow channels, the volume of fluid (VOF) method was employed to simulate the air–water flow in a 3D cuboid channel with a 1.0mm×1.0mm square cross section and a 100mm in length. The microstructure of gas diffusion layers (GDLs) was simplified by a number of representative opening pores on the 2D GDL surface. Water was injected from those pores to simulate water generation by the electrochemical reaction at the cathode side. Operating conditions and material properties were selected according to realistic fuel cell operating conditions. The water injection rate was also amplified 10 times, 100 times and 1000 times to study the flow pattern formation and transition in the channel. Simulation results show that, as the flow develops, the flow pattern evolves from corner droplet flow to top wall film flow, then annular flow, and finally slug flow. The total pressure drop increases exponentially with the increase in water volume fraction, which suggests that water accumulation should be avoided to reduce parasitic energy loss. The effect of material wettability was also studied by changing the contact angle of the GDL surface and channel walls, separately. It is shown that using a more hydrophobic GDL surface is helpful to expel water from the GDL surface, but increases the pressure drop. Using a more hydrophilic channel wall reduces the pressure drop, but increases the water residence time and water coverage of the GDL surface.

Curvature induced flow pattern transitions in serpentine mini-channels

Experimental investigation of the phase interactions in two-phase mini-channel serpentine systems is performed with a focus on determining the effect of radius of curvature of the serpentine on two-phase flow pattern transitions. The initial formation of two-phase flow patterns in T-junction contactors and the resulting effect on the flow through serpentine geometries are studied to predict the initiation of bubble breakup and/or coalescence in planar serpentine arrangements. Bubble breakup maps are developed for each of the serpentine geometries, identifying curvature-induced shifts in the transitions between flow patterns. Single-phase dimensionless analysis for curved geometries is extended to two-phase flow to identify the geometric dependence of critical bubble breakup. Further analysis performed shows that the characteristic length for curved geometries encountered in the Dean number for single-phase flow is suitable for capturing the effects of curvature on the initiation of bubble breakup. The dependence of Weber number on the characteristic length is reported and a critical We CDL C = 10 is identified for predicting bubble breakup inception in the serpentine system.

Helical cell motions in a small ice‐covered meander river reach

AbstractThe investigation of the flow field with a pulse‐coherent acoustic Doppler profiler has led to new high resolution observations of the secondary flow pattern occurring in a natural ice‐covered meander reach. Surveys were conducted during two successive winter periods with different ice conditions. Massive frazil ice accumulation was present during one of the survey and its influence on the flow pattern could be assessed. Results show that the primary flow is clearly deflected towards the outer bend. Secondary flows are one order of magnitude less than the primary flow and they display two stacked counter‐rotating helical cells pattern occurring at the entrance of the bend. This pattern is associated with the parabolic shape of the velocity profiles entering the bend. The pattern rapidly evolves downstream, reducing to one helical cell rotating in an opposite direction than what is observed in open channel flows. Flow mixing and morphological non‐uniformity are potential factors governing the development of the helical cells throughout the bend. Our observations show that a similar coherent flow pattern rapidly forms downstream of a massive frazil ice obstruction in the bend. Frazil ice does not constrain the formation of helical flow pattern in river bends. Copyright © 2010 John Wiley & Sons, Ltd.

Numerical simulation of air–water flow in gated tunnels

Gated tunnels are among the important hydraulic structures which fulfil various functions. However, due to the high-velocity flow through these structures, critical flow conditions may occur. Generally, physical model studies are performed to optimise the design of these structures which are time consuming and also very expensive. In the present research work a three-dimensional numerical model was used to simulate complicated free-surface air–water flow in gated tunnels. The volume of fluid scheme was used together with the K–ε turbulence model in this simulation. The flow rating curve and air demand downstream of the service gate were computed at different gate openings and were compared with experimental data with good agreement. In addition a comparison of the calculated pressure distribution and cavitation index in the gate chamber with physical measurements showed the accuracy of the computational fluid dynamics model. Furthermore, a comparison of flow pattern and rooster tail formation downstream of the gate with experimental observations showed the capability of the numerical model in simulating the complex air–water flow in high-speed gated tunnels. This study shows the application of numerical simulation as a powerful tool in the design of hydraulic structures.