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Flow Visualization (flow + visualization)
Terms modified by Flow Visualization Selected AbstractsPhysically-based Dye Advection for Flow VisualizationCOMPUTER GRAPHICS FORUM, Issue 3 2008Guo-Shi Li Abstract Dye advection is widely used in experimental flow analysis but has seen less use for visualization in computational fluid dynamics. One possible reason for this disconnect is the inaccuracy of the texture-based approach, which is prone to artifacts caused by numeric diffusion and mass fluctuation. In this paper, we introduce a novel 2D dye advection scheme for flow visualization based on the concept of control volume analysis typically used in computational fluid dynamics. The evolution of dye patterns in the flow field is achieved by advecting individual control volumes, which collectively cover the entire spatial domain. The local variation of dye material, represented as a piecewise quasi-parabolic function, is integrated within each control volume resulting in mass conserving transport without excessive numerical diffusion. Due to its physically based formulation, this approach is capable of conveying intricate flow structures not shown in the traditional dye advection schemes while avoiding visual artifacts. [source] Multimodal Flow Visualization and Optimization of Pneumatic Blood Pump for Sorbent Hemodialysis SystemARTIFICIAL ORGANS, Issue 4 2009Fangjun Shu Abstract:, Renal Solutions Allient Sorbent Hemodialysis System utilizes a two-chambered pneumatic pump (Pulsar Blood Pump, Renal Solutions, Inc., Warrendale, PA, USA) to avoid limitations associated with peristaltic pumping systems. Single-needle access is enabled by counter-pulsing the two pump chambers, thereby obviating compliance chambers or blood reservoirs. Each chamber propels 20 cc per pulse of 3 s (dual access) or 6 s (single access) duration, corresponding to a peak Reynolds number of approximately 8000 (based on inlet velocity and chamber diameter). A multimodal series of flow visualization studies (tracer particle, dye washout, and dye erosion) was conducted on a sequence of pump designs with varying port locations and diaphragms to improve the geometry with respect to risk of thrombogenesis. Experiments were conducted in a simplified flow loop using occluders to simulate flow resistance induced by tubing and dialyzer. Tracer visualization revealed flow patterns and qualitatively indicated turbulence intensity. Dye washout identified dwell volume and areas of flow stagnation for each design. Dye erosion results indicated the effectiveness and homogeneity of surface washing. Compared to a centered inlet which resulted in a fluid jet that produced two counter-rotating vortices, a tangential inlet introduced a single vortex, and kept the flow laminar. It also provided better surface washing on the pump inner surface. However, a tangential outlet did not present as much benefit as expected. On the contrary, it created a sharp defection to the flow when transiting from filling to ejection. [source] Time-Adaptive Lines for the Interactive Visualization of Unsteady Flow Data SetsCOMPUTER GRAPHICS FORUM, Issue 8 2009N. Cuntz I.3.3 [Computer Graphics]: Line and Curve Generation; I.3.1 [Computer Graphics]: Parallel Processing Abstract The quest for the ideal flow visualization reveals two major challenges: interactivity and accuracy. Interactivity stands for explorative capabilities and real-time control. Accuracy is a prerequisite for every professional visualization in order to provide a reliable base for analysis of a data set. Geometric flow visualization has a long tradition and comes in very different flavors. Among these, stream, path and streak lines are known to be very useful for both 2D and 3D flows. Despite their importance in practice, appropriate algorithms suited for contemporary hardware are rare. In particular, the adaptive construction of the different line types is not sufficiently studied. This study provides a profound representation and discussion of stream, path and streak lines. Two algorithms are proposed for efficiently and accurately generating these lines using modern graphics hardware. Each includes a scheme for adaptive time-stepping. The adaptivity for stream and path lines is achieved through a new processing idea we call ,selective transform feedback'. The adaptivity for streak lines combines adaptive time-stepping and a geometric refinement of the curve itself. Our visualization is applied, among others, to a data set representing a simulated typhoon. The storage as a set of 3D textures requires special attention. Both algorithms explicitly support this storage, as well as the use of precomputed adaptivity information. [source] Particle Level Set Advection for the Interactive Visualization of Unsteady 3D FlowCOMPUTER GRAPHICS FORUM, Issue 3 2008Nicolas Cuntz Abstract Typically, flow volumes are visualized by defining their boundary as iso-surface of a level set function. Grid-based level sets offer a good global representation but suffer from numerical diffusion of surface detail, whereas particle-based methods preserve details more accurately but introduce the problem of unequal global representation. The particle level set (PLS) method combines the advantages of both approaches by interchanging the information between the grid and the particles. Our work demonstrates that the PLS technique can be adapted to volumetric dye advection via streak volumes, and to the visualization by time surfaces and path volumes. We achieve this with a modified and extended PLS, including a model for dye injection. A new algorithmic interpretation of PLS is introduced to exploit the efficiency of the GPU, leading to interactive visualization. Finally, we demonstrate the high quality and usefulness of PLS flow visualization by providing quantitative results on volume preservation and by discussing typical applications of 3D flow visualization. [source] Physically-based Dye Advection for Flow VisualizationCOMPUTER GRAPHICS FORUM, Issue 3 2008Guo-Shi Li Abstract Dye advection is widely used in experimental flow analysis but has seen less use for visualization in computational fluid dynamics. One possible reason for this disconnect is the inaccuracy of the texture-based approach, which is prone to artifacts caused by numeric diffusion and mass fluctuation. In this paper, we introduce a novel 2D dye advection scheme for flow visualization based on the concept of control volume analysis typically used in computational fluid dynamics. The evolution of dye patterns in the flow field is achieved by advecting individual control volumes, which collectively cover the entire spatial domain. The local variation of dye material, represented as a piecewise quasi-parabolic function, is integrated within each control volume resulting in mass conserving transport without excessive numerical diffusion. Due to its physically based formulation, this approach is capable of conveying intricate flow structures not shown in the traditional dye advection schemes while avoiding visual artifacts. [source] Instabilities during batch sedimentation in geometries containing obstacles: A numerical and experimental study,INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2007Rekha R. Rao Abstract Batch sedimentation of non-colloidal particle suspensions is studied with nuclear magnetic resonance flow visualization and continuum-level numerical modelling of particle migration. The experimental method gives particle volume fraction as a function of time and position, which then provides validation data for the numerical model. A finite element method is used to discretize the equations of motion, including an evolution equation for the particle volume fraction and a generalized Newtonian viscosity dependent on local particle concentration. The diffusive-flux equation is based on the Phillips model (Phys. Fluids A 1992; 4:30,40) and includes sedimentation terms described by Zhang and Acrivos (Int. J. Multiphase Flow 1994; 20:579,591). The model and experiments are utilized in three distinct geometries with particles that are heavier and lighter than the suspending fluid, depending on the experiment: (1) sedimentation in a cylinder with a contraction; (2) particle flotation in a horizontal cylinder with a horizontal rod; and (3) flotation around a rectangular inclusion. Secondary flows appear in both the experiments and the simulations when a region of higher density fluid is above a lower density fluid. The secondary flows result in particle inhomogeneities, Rayleigh,Taylor-like instabilities, and remixing, though the effect in the simulations is more pronounced than in the experiments. Published in 2007 by John Wiley & Sons, Ltd. [source] Study on factors influencing stagnation point offset of turbulent opposed jetsAICHE JOURNAL, Issue 10 2010Wei-Feng Li Abstract Turbulent opposed jets were experimentally studied by the hot-wire anemometer measurement, the smoke-wire flow visualization, and the CFD simulation at L = 1,20D (where L is the nozzle separation and D is the nozzle diameter) and Re > 4500. The instability pattern of turbulent opposed jets was identified by investigating the smoke-wire photos recorded by a high-speed camera. The factors affecting stagnation point offset, such as the bulk velocity, the velocity profile, and the turbulence intensity at the nozzle exits were investigated. Results show that the stagnation point offset is the main instability regime of turbulent opposed jets. Uniform exit velocity profile and increasing exit turbulence intensity will decrease the stagnation point offset of turbulent opposed jets. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Mixing of shear-thinning fluids with yield stress in stirred tanksAICHE JOURNAL, Issue 7 2006P. E. Arratia Abstract Mixing of shear-thinning fluids with yield stress is investigated in a three-dimensional (3-D) flow both in experiments and in simulations. Experiments are conducted in a stirred tank using tracer visualization and velocity measurements. Bulk flow visualization shows the familiar cavern formation around the impeller with stagnant zones surrounding it. Detailed flow visualization inside caverns reveals the main ingredients of chaotic flow: lobe formation, stretching, folding, and self-similar mixing patterns. For multiple impeller systems, however, we find strong compartmentalization characterized by robust segregation between adjacent caverns, hindering mixing performance. Mixing efficiency is enhanced by moving the shaft off-center, which breaks spatial symmetry. The displacement of the shaft from the tank centerline has a beneficial effect on manifold structure: segregated regions are destroyed, separatrices are eliminated, and axial circulation is improved. Numerical simulations are performed by solving the incompressible Reynolds Averaged Navier Stokes equation with a Galerkin Least-Squares finite-element formulation and a macroscopic rheological model. Simulations are able to capture the main features of the flow and are used to investigate stretching statistics and scale behavior. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] WATER MOTION, MARINE MACROALGAL PHYSIOLOGY, AND PRODUCTIONJOURNAL OF PHYCOLOGY, Issue 3 2000Catriona L. Hurd Water motion is a key determinant of marine macroalgal production, influencing directly or indirectly physiological rates and community structure. Our understanding of how marine macroalgae interact with their hydrodynamic environment has increased substantially over the past 20 years, due to the application of tools such as flow visualization to aquatic vegetation, and in situ measurements of seawater velocity and turbulence. This review considers how the hydrodynamic environment in which macroalgae grow influences their ability to acquire essential resources and how macroalgae might respond physiologically to fluctuations in their hydrodynamic regime with a focus on: (1) the biochemical processes occurring within the diffusion boundary layer (DBL) that might reduce rates of macroalgal production; (2) time scales over which measurements of velocity and DBL processes should be made, discussing the likelihood of in situ mass transfer limitation; (3) if and how macroalgal morphology influences resource acquisition in slow flows; and (4) ecobiomechanics and how hydrodynamic drag might influence resource acquisition and allocation. Finally, the concept that macroalgal production is enhanced in wave-exposed versus sheltered habitats is discussed. [source] Rapid quantitation of cardiovascular flow using slice-selective fourier velocity encoding with spiral readoutsMAGNETIC RESONANCE IN MEDICINE, Issue 4 2007Joao L. A. Carvalho Abstract Accurate flow visualization and quantitation is important for the assessment of many cardiovascular conditions such as valvular stenosis and regurgitation. Phase contrast based methods experience partial volume artifacts when flow is highly localized, complex and/or turbulent. Fourier velocity encoding (FVE) avoids such problems by resolving the full velocity distribution within each voxel. This work proposes the use of slice selective FVE with spiral readouts to acquire fully localized velocity distributions in a short breath-hold. Scan-plane prescription is performed using classic protocols, and an automatic algorithm is used for in-plane localization of the flow. Time and spatially-resolved aortic valve velocity distributions with 26-msec temporal resolution and 25 cm/sec velocity resolution over a 600 cm/sec field-of-view were acquired in a 12-heartbeat breath-hold. In carotid studies, scan time was extended to achieve higher spatial resolution. The method was demonstrated in healthy volunteers and patients, and the results compared qualitatively well with Doppler ultrasound. Acquisition time could be reduced to 7 heartbeats (a 42% reduction) using partial Fourier reconstruction along the velocity dimension. Magn Reson Med 57:639,646, 2007. © 2007 Wiley-Liss, Inc. [source] Drop Deformation and Breakup Mechanisms in Viscoelastic Model Fluid Systems and Polymer BlendsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2002Frej Mighri Abstract This paper reviews the dispersion mechanisms in viscoelastic systems under relatively high shear rate conditions. In particular, two non-Newtonian deformation and breakup mechanisms were revealed by flow visualization in a transparent Couette shearing setup. The first one is the dispersed droplet elongation perpendicular to the flow direction. This was observed only for viscoelastic drops and had been associated to normal force buildup in the droplet. The second deformation/breakup mechanism was observed in very high viscosity ratio polymer systems. It consists in erosion at the drop surface. Clouds of very small ribbons and sheets were developed around the drop then stretched and finally broken into very small droplets, rapidly distributed in the matrix. Cet article examine les mécanismes de dispersion dans les mélanges viscoélastiques à des taux de cisaillement relativement élevés. Deux nouveaux mécanismes de déformation et de rupture de gouttes viscoélastiques ont été révélés en utilisant un montage de visualisation transparent de type Couette. Le premier mécanisme est l'orientation de l'axe principal de la goutte perpendiculairement à la direction de l'écoulement, phénomène qui n'a été observé que pour des gouttes viscoélastiques. Ce phénomène a été relié au développement de forces normales (élasticité) à l'intérieur de la goutte. Le second mécanisme de déformation/rupture a été observé avec des systèmes de polymères fondus possédant des rapports de viscosité élevés. Il consistait en une érosion de la surface de la goutte générant ainsi un nuage de gouttelettes et de minces feuillets autour de la goutte principale. Ces derniers s'étiraient suite à l'écoulement de la matrice et finissaient par être brisés en gouttelettes très fines rapidement dispersées dans la matrice. [source] Self-sustained oscillations in opposed impinging jets in an enclosureTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2000David A. Johnson Abstract The flow of jets in confining enclosures has significant application in many engineering processes. In particular, the impingement of axisymmetric jets in a confined space has been examined using flow visualization, laser Doppler anemometry, and numerical simulations. Several flow regions were found; stable steady, regular oscillatory, and irregular oscillatory. Initially, a steady flow field existed for all arrangements for Red < ,90 (based on the nozzle diameter d, the fluid kinematic viscosity v and the volumetric flow rate Q through the nozzle (Q = ,d2/4Uavg)) but subsequent increments in the fluid velocity caused a regularly oscillating flow field to emerge. The onset of the oscillations and the upper limit of finite oscillations were found to be a function of the Red, and the nozzle diameter to chamber dimension ratio. Steady numerical simulations predicted the steady flow field well and good agreement was obtained in unsteady simulations of the oscillating flow field. The oscillating flow field is considered to be a class of self-sustaining oscillations where instabilities in the jet shear layer are amplified because of feed back from pressure disturbances in the impingement region. L'écoulement de jets dans des espaces confinés a des applications importantes dans de nombreux precédés d'ingénierie. On a examiné en particulier la collision de jets axisymétriques dans un espace confiné au moyen de la visualisation des écoulements, de l'anémométrie par laser Doppler et de simulations numériques. On a trouvé plusieurs régions d'écoulement : stable-stationnaire, régulier-oscillatoire et irrégulier-oscillatoire. Initialement, il existe un champ d'écoulement stationnaire pour toutes les configurations lorsque Red < ,90 (basé sur le diamètre de tuyère d, la viscosité cinématique du fluide (et le débit volumétrique Q dans la tuyère (Q = ,d24Uavg)); mais une augmentation subséquente de la vitesse du fluide déclenche un champ d'écoulement oscillatoire régulier. On a trouvé que l'apparition des oscillations et la limite supérieure des oscillations finies sont fonction de Red et du rapport entre le diamètre de l'orifice et la dimension de la chambre. Des simulations numériques stationnaires prédisent bien le champ d'écoulement stationnaire et un bon accord est obtenu pour des simulations non stationnaires du champ d'écoulement oscillant. Le champ d'écoulement oscillant est considéré être une catégorie d'oscillations qui se maintiennent seules dans laquelle les instabilités dans la couche de cisaillement des jets sont amplifiés par un effet retour des perturbations de pression dans la région de collision. [source] Effect of radial angle on mixing time for a double jet mixerASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010P. Manjula Abstract Mixing is one of the common unit operations employed in chemical industries. It is used for blending of liquids, flocculation, homogenization of mixtures, ensuring proper heat and mass transfer in various operations, prevention of deposition of solid particles, etc. Earlier research aspects were focused on experimental estimation of mixing time and proposing suitable correlations for the prediction of mixing time, the recent one being on flow visualization. However, most of the results reported in the literature deal with liquid flow with multi jets, whereas the effect of radial angle on mixing time was not studied. This study describes the effect of radial angle on mixing time as determined by experiment and simulation. A computational fluid dynamics (CFD) modeling is done for a jet mixing tank having two jets for a water,water system. Nozzle configuration for jet1 was fixed on the basis of our earlier studies (2/3rd position, flow rate 9l/m, nozzle angle 45° and nozzle diameter 10 mm). Mixing times were estimated for different jet2 configurations (jet angle 30°, 45° and 60°; radial angles 60°, 120°, 180°) located at different tank heights (2/3rd and 1/3rd from the bottom of the tank). The results obtained for mixing time for jet mixing in a tank with two jets are analyzed and the suitable nozzle angle, radial angle and position are proposed for the jet2 of the jet mixer considered in the present study. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Numerical simulation of the unsteady flow over an elliptic cylinder at different orientationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2001H. M. Badr Abstract A numerical method is developed for investigating the two-dimensional unsteady viscous flow over an inclined elliptic cylinder placed in a uniform stream of infinite extent. The direction of the free stream is normal to the cylinder axis and the flow field unsteadiness arises from two effects, the first is due to the flow field development following the start of the motion and the second is due to vortex shedding in the wake region. The time-dependent flow is governed by the full conservation equations of mass and momentum with no boundary layer approximations. The parameters involved are the cylinder axis ratio, Reynolds number and the angle of attack. The investigation covers a Reynolds number range up to 5000. The minor,major axis ratio of the elliptic cylinder ranges between 0.5 and 0.6, and the angle of attack ranges between 0° and 90°. A series truncation method based on Fourier series is used to reduce the governing Navier,Stokes equations to two coupled infinite sets of second-order differential equations. These equations are approximated by retaining only a finite number of terms and are then solved by approximating the derivatives using central differences. The results reveal an unusual phenomenon of negative lift occurring shortly after the start of motion. Various comparisons are made with previous theoretical and experimental results, including flow visualizations, to validate the solution methodology. Copyright © 2001 John Wiley & Sons, Ltd. [source] Viscous co-current downward Taylor flow in a square mini-channelAICHE JOURNAL, Issue 7 2010Özge Keskin Abstract This article presents a computational study of the co-current downward Taylor flow of gas bubbles in a viscous liquid within a square channel of 1 mm hydraulic diameter. The three-dimensional numerical simulations are performed with an in-house computer code, which is based on the volume-of-fluid method with interface reconstruction. The computed (always axi-symmetric) bubble shapes are validated by experimental flow visualizations for varying capillary number. The evaluation of the numerical results for a series of simulations reveals the dependence of the bubble diameter and the interfacial area per unit volume on the capillary number. Correlations between bubble velocity and total superficial velocity are also provided. The present results are useful to estimate the values of the bubble diameter, the liquid film thickness and the interfacial area per unit volume from given values of the gas and liquid superficial velocities. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] | |||||||||||||