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Flow Structures (flow + structure)

Distribution by Scientific Domains

Engineering	46%
Chemistry	31%
Earth and Environmental Science	15%
Physics and Astronomy	6%

Selected Abstracts

Local Bubble Dynamics and Macroscopic Flow Structure in Bubble Columns with Different Scales

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2003
Wei Chen
Abstract Local bubble behaviours were investigated in three bubble columns with different diameters of 200, 400 and 800 mm. By means of a novel single-tip optical fibre probe employing laser Doppler technique, the local gas holdup, bubble frequency, bubble size and velocity were measured simultaneously at different locations of the columns. Measurements were performed in air-water system at superficial gas velocities up to 90 mm/s. The averaged profiles and instantaneous measurements were analyzed and compared for different columns. The presence of a coherent gross circulation structure spanning the entire column diameter in the larger column rather than a pair of symmetrical circulation cells observed in the smaller columns has been confirmed. Les comportements locaux des bulles ont été étudiés dans trois colonnes à bulles de diamètres différents, soient 200, 400 et 800 mm. Au moyen d'une nouvelle sonde à fibre optique à embout unique employant la technique laser Doppler, des mesures locales de la rétention de gaz, de la fréquence des bulles, de la taille des bulles et de la vitesse ont été effectuées simultanément à différents endroits dans les colonnes. Ces mesures ont été effectuées pour un système air-eau à des vitesses de gaz superficielles atteignant 90 mm/s. Les profils moyennés et les mesures instantanées ont été analysés puis comparés pour différentes colonnes. La présence d'une structure de circulation unique cohérente occupant tout le diamètre de la colonne dans la colonne la plus large plutôt qu'une paire de cellules de circulation symétriques observées dans les colonnes plus petites est confirmée. [source]

A Comparison of Flow Dynamics and Flow Structure in a Riser and a Downer

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 4 2007
B. Wu
Abstract Flow development and flow dynamics were systematically investigated using local solids concentration measurements in a pair consisting of a downer (0.1,m I.D., 9.3,m high) and a riser of the same diameter (0.1,m I.D., 15.1,m high). Both statistical and chaos analysis were employed. Values for the Kolmogorov entropy (K), correlation dimension (D), and Hurst exponent (H) were estimated from time series of solids concentration measurements. Axial distributions of chaos parameters were more complex in the downer than those in the riser, especially in the entrance section. Flow in the downer was more uniform with a flatter core in all the radial profiles of chaos parameters. The radial profiles of K varied significantly with increasing axial levels due to different clustering behavior in the wall region of the downer. In both the riser and the downer, anti-persistent flow in the core region and persistent flow behavior near the wall were identified from the profiles of H. Different flow behavior in the region close to the wall in the downer and riser was characterized from the combination of the three chaos parameters. Relationships between chaos parameters and local time-averaged solids holdup in the core and wall regions of the developed sections in both the downer and riser were also analyzed. [source]

An experimental study on the ripple,dune transition

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2001
André Robert
Abstract Flume experiments were conducted on different bed stages across the ripple,dune transition. As flow velocity increases, an initially flat bed surface (made of fairly uniform sandy material) is gradually transformed into a two-dimensional rippled bed. With further increase in velocity, two-dimensional ripples are replaced by irregular, linguoid ripples. As the average velocity necessary for the ripple,dune transition to occur is imposed on the bed surface, these non-equilibrium linguoid ripples are further transformed into larger, two-dimensional dunes. For each of these stages across the transition, a concrete mould of the bed was created and the flow structure above each fixed bed surface investigated. An acoustic Doppler velocimeter was used to study the flow characteristics above each bed surface. Detailed profiles were used along a transect located in the middle of the channel. Results are presented in the form of spatially averaged profiles of various flow characteristics and of contour maps of flow fields (section view). They clearly illustrate some important distinctions in the flow structure above the different bedform types associated with different stages during the transition. Turbulence intensity and Reynolds stresses gradually increase throughout the transition. Two-dimensional ripples present a fairly uniform spatial distribution of turbulent flow characteristics above the bed. Linguoid ripples induce three-dimensional turbulence structure at greater heights above the bed surface and turbulence intensity tends to increase steadily with height above bed surface in the wake region. A very significant increase in turbulence intensity and momentum exchange occurs during the transition from linguoid ripples to dunes. The turbulent flow field properties above dunes are highly dependent on the position along and above the bed surface and these fields present a very high degree of spatial variability (when compared with the rippled beds). Further investigations under natural conditions emphasizing sediment transport mechanisms and rates during the transition should represent the next step of analysis, together with an emphasis on quadrant analysis. Copyright © 2001 John Wiley & Sons, Ltd. [source]

The effect of jet array arrangement on the flow characteristics of the outlet hole in short confined channels

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2008
Liu Haiyong
Abstract This experimental study is part of the research program related to the aerodynamic characteristics of impingement in a confined channel. Experimental research on better understanding flow structure in confined channel with impingement cooling is rarely found in open literature. The main purposes of this project are (1) gaining greater insight into the structure of the impingement jet flow and flow in the outlet hole; (2) understanding the effect of impingement hole arrangement build up on the flow structure and aerodynamic parameters within holes and channels with different aspect ratios. The test models are two confined channels with three staggered circular jet holes, and a single large size outlet hole placed downstream of the jet plate. The structure parameters of these orifices are different. In this paper, detailed flow field in the outlet hole was measured with a straight five-hole probe, and the discharge coefficient of outlet holes with different aspect ratios was also studied in each channel. Experimental data shows that the jet arrangement has little influence on the flow behavior of the outlet hole when the aspect ratio of the passage was 1, but it played an important role on the discharge coefficient. Distinctively different flow patterns were found in two models with the aspect ratios of 3 and 5, while the variation of the discharge coefficient showed a slight influence on impingement hole arrangement. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(1): 20,28, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20188 [source]

An unsteady flow structure on a heated rotating disk under mixed convection

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 6 2005
Noriyuki Furuichi
Abstract A flow field under mixed convection on a heated rotating disk has been measured using an ultrasonic velocity profiler (UVP). The measured velocity field is a spatio-temporal one as a function of radial coordinates and time. The objective of this paper is to clarify the vortex structure caused by the instability between buoyancy and centrifugal force. The vortex appears under typical conditions of Reynolds numbers and Grashof numbers and it moves toward the outside of the disk. This behavior can be classified into two patterns. The size of the vortex structure decreases with an increasing Reynolds number and increases with the Grashof number. The traveling velocity of the vortex increases with the Grashof number. Moreover, it decreases with an increasing Reynolds number in spite of increasing centrifugal force. According to these results, the region dominated by natural, forced, and mixed convection is classified in the relationship between Reynolds and Grashof numbers. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(6): 407,418, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20074 [source]

Unstructured grid generation using LiDAR data for urban flood inundation modelling

HYDROLOGICAL PROCESSES, Issue 11 2010
Ryota Tsubaki
Abstract Inundation disasters, caused by sudden water level rise or rapid flow, occur frequently in various parts of the world. Such catastrophes strike not only in thinly populated flood plains or farmland but also in highly populated villages or urban areas. Inundation of the populated areas causes severe damage to the economy, injury, and loss of life; therefore, a proper management scheme for the disaster has to be developed. To predict and manage such adversity, an understanding of the dynamic processes of inundation flow is necessary because risk estimation is performed based on inundation flow information. In this study, we developed a comprehensive method to conduct detailed inundation flow simulations for a populated area with quite complex topographical features using LiDAR (Light Detection and Ranging) data. Detailed geospatial information including the location and shape of each building was extracted from the LiDAR data and used for the grid generation. The developed approach can distinguish buildings from vegetation and treat them differently in the flow model. With this method, a fine unstructured grid can be generated representing the complicated urban land features precisely without exhausting labour for data preparation. The accuracy of the generated grid with different grid spacing and grid type is discussed and the optimal range of grid spacing for direct representation of urban topography is investigated. The developed method is applied to the estimation of inundation flows, which occurred in the basin of the Shin-minato River. A detailed inundation flow structure is represented by the flow model, and the flow characteristics with respect to topographic features are discussed. Copyright © 2010 John Wiley & Sons, Ltd. [source]

1-D numerical modelling of shallow flows with variable horizontal density

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2010
Feifei Zhang Leighton
Abstract A1-D numerical model is presented for vertically homogeneous shallow flows with variable horizontal density. The governing equations represent depth-averaged mass and momentum conservation of a liquid,species mixture, and mass conservation of the species in the horizontal direction. Here, the term ,species' refers to material transported with the liquid flow. For example, when the species is taken to be suspended sediment, the model provides an idealized simulation of hyper-concentrated sediment-laden flows. The volumetric species concentration acts as an active scalar, allowing the species dynamics to modify the flow structure. A Godunov-type finite volume scheme is implemented to solve the conservation laws written in a deviatoric, hyperbolic form. The model is verified for variable-density flows, where analytical steady-state solutions are derived. The agreement between the numerical predictions and benchmark test solutions illustrates the ability of the model to capture rapidly varying flow features over uniform and non-uniform bed topography. A parameter study examines the effects of varying the initial density and depth in different regions. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Numerical analysis on the propulsive performance and vortex shedding of fish-like travelling wavy plate

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2005
Gen-Jin Dong
Abstract Numerical analysis is carried out to investigate viscous flow over a travelling wavy plate undergoing lateral motion in the form of a streamwise travelling wave, which is similar to the backbone undulation of swimming fish. The two-dimensional incompressible Navier,Stokes equations are solved using the finite element technique with the deforming-spatial-domain/stabilized space,time formulation. The objective of this study is to elucidate hydrodynamic features of flow structure and vortex shedding near the travelling wavy plate and to get into physical insights to the understanding of fish-like swimming mechanisms in terms of drag reduction and optimal propulsive performance. The effects of some typical parameters, including the phase speed, amplitude, and relative wavelength of travelling wavy plate, on the flow structures, the forces, and the power consumption required for the propulsive motion of the plate are analysed. These results predicted by the present numerical analysis are well consistent with the available data obtained for the wave-like swimming motion of live fish in nature. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Influence of inertia, topography and gravity on transient axisymmetric thin-film flow

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2004
Roger E. Khayat
Abstract This study examines theoretically the development of early transients for axisymmetric flow of a thin film over a stationary cylindrical substrate of arbitrary shape. The fluid is assumed to emerge from an annular tube as it is driven by a pressure gradient maintained inside the annulus, and/or by gravity in the axial direction. The interplay between inertia, annulus aspect ratio, substrate topography and gravity is particularly emphasized. Initial conditions are found to have a drastic effect on the ensuing flow. The flow is governed by the thin-film equations of the ,boundary-layer' type, which are solved by expanding the flow field in terms of orthonormal modes in the radial direction. The formulation is validated upon comparison with the similarity solution of Watson (J. Fluid Mech 1964; 20:481) leading to an excellent agreement when only 2,3 modes are included. The wave and flow structure are examined for high and low inertia. It is found that low-inertia fluids tend to accumulate near the annulus exit, exhibiting a standing wave that grows with time. This behaviour clearly illustrates the difficulty faced with coating high-viscosity fluids. The annulus aspect is found to be influential only when inertia is significant; there is less flow resistance for a film over a cylinder of smaller diameter. For high inertia, the free surface evolves similarly to two-dimensional flow. The substrate topography is found to have a significant effect on transient behaviour, but this effect depends strongly on inertia. It is observed that the flow of a high-inertia fluid over a step-down exhibits the formation of a secondary wave that moves upstream of the primary wave. Gravity is found to help the film (coating) flow by halting or prohibiting the wave growth. The initial film profile and velocity distribution dictate whether the fluid will flow downstream or accumulate near the annulus exit. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Numerical simulation of vortical ideal fluid flow through curved channel

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2003
N. P. Moshkin
Abstract A numerical algorithm to study the boundary-value problem in which the governing equations are the steady Euler equations and the vorticity is given on the inflow parts of the domain boundary is developed. The Euler equations are implemented in terms of the stream function and vorticity. An irregular physical domain is transformed into a rectangle in the computational domain and the Euler equations are rewritten with respect to a curvilinear co-ordinate system. The convergence of the finite-difference equations to the exact solution is shown experimentally for the test problems by comparing the computational results with the exact solutions on the sequence of grids. To find the pressure from the known vorticity and stream function, the Euler equations are utilized in the Gromeka,Lamb form. The numerical algorithm is illustrated with several examples of steady flow through a two-dimensional channel with curved walls. The analysis of calculations shows strong dependence of the pressure field on the vorticity given at the inflow parts of the boundary. Plots of the flow structure and isobars, for different geometries of channel and for different values of vorticity on entrance, are also presented. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Effect of pressure on thermal aspects in the riser column of a pressurized circulating fluidized bed

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2006
A. V. S. S. K. S. Gupta
Abstract In the present paper the effect of pressure on bed-to-wall heat transfer in the riser column of a pressurized circulating fluidized bed (PCFB) unit is estimated through a modified mechanistic model. Gas,solid flow structure and average cross-sectional solids concentration play a dominant role in better understanding of bed-to-wall heat transfer mechanism in the riser column of a PCFB. The effect of pressure on average solids concentration fraction ,c' in the riser column is analysed from the experimental investigations. The basic cluster renewal model of an atmospheric circulating fluidized bed has been modified to consider the effect of pressure on different model parameters such as cluster properties, gas layer thickness, cluster, particle, gas phase, radiation and bed-to-wall heat transfer coefficients, respectively. The cluster thermal conductivity increases with system pressure as well as with bed temperature due to higher cluster thermal properties. The increased operating pressure enhances the particle and dispersed phase heat transfer components. The bed-to-wall heat transfer coefficient increases with operating pressure, because of increased particle concentration. The predicted results from the model are compared with the experimentally measured values as well as with the published literature, and a good agreement has been observed. The bed-to-wall heat transfer coefficient variation along the riser height is also reported for different operating pressures. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Thermodynamic optimization of global circulation and climate

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2005
Adrian Bejan
Abstract The constructal law of generation of flow structure is used to predict the main features of global circulation and climate. The flow structure is the atmospheric and oceanic circulation. This feature is modelled as convection loops, and added to the earth model as a heat engine heated by the Sun and cooled by the background. It is shown that the dissipation of the power produced by the earth engine can be maximized by selecting the proper balance between the hot and cold zones of the Earth, and by optimizing the thermal conductance of the circulation loops. The optimized features agree with the main characteristics of global circulation and climate. The robustness of these predictions, and the place of the constructal law as a self-standing principle in thermodynamics, are discussed. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Gas-solids flow behavior: CFB riser vs. downer

AICHE JOURNAL, Issue 9 2001
H. Zhang
Comparisons are made in a circulating fluidized-bed riser/downer system between a 15.1 m high, 0.10 m ID riser and a 9.3 m high, 0.10 m ID downer, based on the measurements of the radial distributions of the local solids holdups and local particle velocities along the two columns. Although the core-annulus flow structures exist in both the riser and downer, the radial flow structure in the downer differs largely from that in the riser. The radial distributions of solids holdup and particle velocity in the downer are much more uniform than those in the riser, thus ensuring the low back mixing and the narrow particle residence time distribution in the downer. The axial flow structure in the downer is also more uniform than that in the riser. Due to the high particle acceleration and the high particle velocity in the downer, the overall solids holdup is significantly lower than that in the riser. The microflow structure in the downer, characterized by the low intermittency indices, is also more uniform than that in the riser. These key properties of the downer make it a very promising candidate for industrial applications where short reaction times and high product selectivity are required. [source]

Numerical simulations of type III planetary migration , I. Disc model and convergence tests

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
A. Pepli
ABSTRACT We investigate the fast (type III) migration regime of high-mass protoplanets orbiting in protoplanetary discs. This type of migration is dominated by corotational torques. We study the details of flow structure in the planet's vicinity, the dependence of migration rate on the adopted disc model and the numerical convergence of models (independence of certain numerical parameters such as gravitational softening). We use two-dimensional hydrodynamical simulations with adaptive mesh refinement, based on the flash code with improved time-stepping scheme. We perform global disc simulations with sufficient resolution close to the planet, which is allowed to freely move throughout the grid. We employ a new type of equation of state in which the gas temperature depends on both the distance to the star and planet, and a simplified correction for self-gravity of the circumplanetary gas. We find that the migration rate in the type III migration regime depends strongly on the gas dynamics inside the Hill sphere (Roche lobe of the planet) which, in turn, is sensitive to the aspect ratio of the circumplanetary disc. Furthermore, corrections due to the gas self-gravity are necessary to reduce numerical artefacts that act against rapid planet migration. Reliable numerical studies of type III migration thus require consideration of both the thermal and the self-gravity corrections, as well as a sufficient spatial resolution and the calculation of disc,planet attraction both inside and outside the Hill sphere. With this proviso, we find type III migration to be a robust mode of migration, astrophysically promising because of a speed much faster than in the previously studied modes of migration. [source]

Radial nonuniformity index (RNI) in fluidized beds and other multiphase flow systems

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2001
Jing-Xu (Jesse) Zhu
Abstract The radial nonuniformity index (RNI) is a new non-dimensional index recently devised to quantify the extent of radial variations of flow parameters in fluidized beds and other multiphase flow systems. The index, defined as the ratio of the standard deviation of the given flow parameter in the radial direction to the maximum practically possible standard deviation of that particular parameter, is shown to be an excellent measure of the radial flow structure. This index allows the use of a single value to summarize the radial variation of a given flow parameter. The higher the value of the RNI the less uniform is the flow, and vice versa. Using this technique, radial distributions of local solids concentration and particle velocities from different circulating fluidized bed systems (gas-solid and liquid-solid, upflow and downflow) were examined. It has been found that the RNI can be confidently related to the flow conditions in the circulating fluidized beds, and more insight understanding has been achieved. L'indice de non-uniformité radiale (RNI) est un nouvel indice adimensionnel introduit récemment pour quantifier l'étendue des variations radiales des paramètres d'écoulement dans les lits fluidisés et autres systèmes d'écoulement multiphasiques. On montre que cet indice, défini comme le rapport entre I'écart type du paramètre d'écoulement donné dans la direction radiale et I'écart type maximum pratiquement possible de ce paramètre particulier, est une excellente mesure de la structure d'écoulement radial. Il permet I'utilisation d'une valeur unique pour décrire la variation radiale d'un paramètre d'écoulement donné. Plus la valeur de RNI est élevée, moins I'écoulement est uniforme, et vice-versa. À I'aide de cette technique, on a examiné les distributions radiales des concentrations de solides locales et des vitesses de particules pour différents systèmes de lits fluidisés circulants (gaz-solide et liquide-solide, ascendant et descendant). On a trouvé que le RNI pouvait ,tre relié en toute confiance aux conditions d'écoulement dans les lits fluidisés circulants, ce qui permet de mieux comprendre ce problème. [source]

Numerical study of influences of buoyancy and solutal Marangoni convection on flow structures in a germanium-silicon floating zone

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2005
K. Lin
Abstract This paper presents a numerical study of Marangoni flows in a floating zone of germanium-silicon crystals, which was performed by using a commercial finite element program FIDADTM. The numerical results point out that for fluids with a small Pr number the influence of buoyancy forces cannot be ignored in the numerical model. Furthermore, the competition between the thermocapillary (TC) and solutocapillary (SC) flows in the floating zones was qualitatively examined. If the TC flow is as strong as that in the Si-rich floating zone, the SC flow may be restricted to the bottom area near the free surface. Otherwise, the SC flow may overcome the TC flow and induce a surface transfer of species. The numerical predictions agree well with the previous experiment results. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Field mapping and digital elevation modelling of submerged and unsubmerged hydraulic jump regions in a bedrock step,pool channel

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2006
Brett L. Vallé
Abstract High-resolution tacheometric field surveying was integrated with computer-assisted drafting to visualize and contrast three-dimensional bed and water surface digital elevation models (DEMs) for submerged and unsubmerged hydraulic jump regions in a bedrock step,pool channel. Measurements were conducted for two discharge conditions. Since previous applica-tions of three-dimensional field mapping and digital elevation modelling of stream channels have been limited to smoothly contiguous gravel-bedded systems, surveying was optimized by topographic setting and scaled to localized bed and water surface discontinuities. Traces and visualizations of the jump regions indicated that dichotomous decimetre shifts in water surface topography occurred for both jump regions from lower to higher discharges. Systematic removal of the survey points and DEM differencing indicated that point densities of ten points per square metre, in conjunction with a survey structure targeting grade breaks of 0·3,0·5 m, were required to capture decimetre form variations of the natural jump regions. The DEMs highlight the importance of recognizing the relationship between transcritical flow structures and localized topographic heterogeneities in bedrock channels. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Spatial patterns of water surface topography at a river confluence

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2002
Dr Pascale M. Biron
Abstract Understanding flow structures in river confluences has largely been the product of interpretations made from measured flow velocity data. Here, we turn the attention to the investigation of the patterns of both the average and standard deviations of the micro-topography of the water surface at an asymmetrical natural discordant confluence for different flow conditions. Water surface topography is measured using a total station to survey the position of a reflector mounted on a custom-built raft. To limit error problems related to changes in the water level, measurements are taken and analysed by cross-stream transects where five water surface profiles are taken before moving to the next transect. Three-dimensional numerical simulations of the flow dynamics at the field site are used to examine predicted water surface topography for a steady-state situation. The patterns are interpreted with respect to flow structure dynamics, visual observations of boils, and bed topography. Results indicate that coherent patterns emerge at the water surface of a discordant bed confluence for different flow conditions. The zone of stagnation and the mixing layer are characterized by super-elevation, a lateral tilt is present at the edge of the mixing layer, and a zone of super-elevation is present on the tributary side at the downstream junction corner. The latter seems associated with periodical upwelling and is not present in the numerical simulations that do not take into account instantaneous velocity fluctuations. Planform curvature, topographic steering related to the tributary mouth bar, and turbulent structures associated with the mixing layer all play a key role in the pattern of both the average and standard deviation of the water surface topography at confluences. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Hemodynamic analysis of intracranial aneurysms with moving parent arteries: Basilar tip aneurysms

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 10 2010
Daniel M. Sforza
Abstract The effects of parent artery motion on the hemodynamics of basilar tip saccular aneurysms and its potential effect on aneurysm rupture were studied. The aneurysm and parent artery motions in two patients were determined from cine loops of dynamic angiographies. The oscillatory motion amplitude was quantified by registering the frames. Patient-specific computational fluid dynamics (CFD) models of both aneurysms were constructed from 3D rotational angiography images. Two CFD calculations were performed for each patient, corresponding to static and moving models. The motion estimated from the dynamic images was used to move the surface grid points in the moving model. Visualizations from the simulations were compared for wall shear stress (WSS), velocity profiles, and streamlines. In both patients, a rigid oscillation of the aneurysm and basilar artery in the anterio-posterior direction was observed and measured. The distribution of WSS was nearly identical between the models of each patient, as well as major intra-aneurysmal flow structures, inflow jets, and regions of impingement. The motion observed in pulsating intracranial vasculature does not have a major impact on intra-aneurysmal hemodynamic variables. Parent artery motion is unlikely to be a risk factor for increased risk of aneurysmal rupture. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Turbulence in a three-dimensional wall-bounded shear flow

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2010
A. Holstad
Abstract A new turbulent flow with distinct three-dimensional characteristics has been designed in order to study the impact of mean-flow skewing on the turbulent coherent vortices and Reynolds-averaged statistics. The skewing of a unidirectional plane Couette flow was achieved by means of a spanwise pressure gradient. Direct numerical simulations of the statistically steady Couette,Poiseuille flow enabled in-depth explorations of the turbulence field in the skewed flow. The imposition of a modest spanwise gradient turned the mean flow about 8° away from the original Couette flow direction and this turning angle remained nearly the same over the entire cross section. Nevertheless, a substantial non-alignment between the turbulent shear stress angle and the mean velocity gradient angle was observed. The structure parameter turned out to slightly exceed that in the pure Couette flow, contrary to the observations made in some other three-dimensional shear flows. Coherent flow structures, which are known to be associated with the Reynolds shear stress in near-wall regions, were identified by the ,2 -criterion. Instantaneous and ensemble-averaged vortices resembled those found in the unidirectional Couette flow. In the skewed flow, however, the vortex structures were turned to align with the local mean-flow direction. The conventional symmetry between Case 1 and Case 2 vortices was broken due to the mean-flow three-dimensionality. The turning of the coherent vortices and the accompanying symmetry-breaking gave rise to secondary and tertiary turbulent shear stress components. By averaging the already ensemble-averaged shear stresses associated with Case 1 and Case 2 vortices in the homogeneous directions, a direct link between the educed near-wall structures and the Reynolds-averaged turbulent stresses was established. These observations provide evidence in support of the hypothesis that the structural model proposed for two-dimensional turbulent boundary layers remains valid also in flows with moderate mean three-dimensionality. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Numerical analysis on the propulsive performance and vortex shedding of fish-like travelling wavy plate

Analysis of super compact finite difference method and application to simulation of vortex,shock interaction

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2001
Fu Dexun
Abstract Turbulence and aeroacoustic noise high-order accurate schemes are required, and preferred, for solving complex flow fields with multi-scale structures. In this paper a super compact finite difference method (SCFDM) is presented, the accuracy is analysed and the method is compared with a sixth-order traditional and compact finite difference approximation. The comparison shows that the sixth-order accurate super compact method has higher resolving efficiency. The sixth-order super compact method, with a three-stage Runge,Kutta method for approximation of the compressible Navier,Stokes equations, is used to solve the complex flow structures induced by vortex,shock interactions. The basic nature of the near-field sound generated by interaction is studied. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Optimization of tree-shaped flow distribution structures over a disc-shaped area

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2003
S. Lorente
Abstract In this paper, we review the fundamental problem of how to design a flow path with minimum overall resistance between one point (O) and many points situated equidistantly on a circle centred at O. This is a fundamental problem in energy engineering: the distribution of fluid, energy, electric power, etc., from points to surrounding areas. This problem is also fundamental in heat transfer and electronics cooling: how to bathe and cool with a single stream of coolant a disc-shaped area or volume that generates heat at every point. This paper outlines, first, a direct route to the construction of effective tree-shaped flow structures. The starting point is the optimization of the shape of each elemental area, such that the length of the flow path housed by the element is minimized. Proceeding towards larger and more complex structures,from elements to first constructs, second constructs, etc.,the paper develops tree-shaped flow structures between one point and a straight line, as an elemental problem, and a circle and its centre. We also consider the equivalent tree-shaped networks obtained by minimizing the pressure drop at every step of the construction, in accordance with geometric constraints. The construction method is applied to a fluid flow configuration with laminar fully developed flow. It is shown that there is little difference between the two methods. The minimal-length structures perform very close to the fully optimized designs. These results emphasize the robustness of optimized tree-shaped flows. Copyright © 2003 John Wiley & Sons, Ltd. [source]

The Cansiwang Melange of Southeast Bohol (Central Philippines): Origin and tectonic implications

ISLAND ARC, Issue 4 2000
Joel V. De Jesus
Abstract The Cansiwang Melange underlies the Southeast Bohol Ophiolite Complex (SEBOC) and is composed mainly of sheared ophiolite-derived blocks such as harzburgites, microgabbros, basalts and cherts in a pervasive serpentinite matrix. Available field, as well as geophysical evidence show that this melange unit is not diapiric, nor does it have a sedimentary origin considering that it lacks slump and flow structures. A tectonic origin for the Cansiwang Melange is favored in view of the numerous thrust faults, which cut across the exposures, as well as the tectonic contacts that the melange has with the overlying and underlying formations. The presence of the Cansiwang Melange in between the SEBOC and the Alicia Schist provides evidence that the amphibolite of the Alicia Schist do not correspond to the metamorphic sole of SEBOC. Similar to what is recognized in the Josephine Ophiolite, this suggests a ,cold' emplacement of the ophiolite over the Alicia Schist. The Cansiwang Melange represents an accretionary prism product which marks the location of an ancient subduction zone in what is now Central Philippines. [source]

Thermal and hydrodynamic characteristics of constructal tree-shaped minichannel heat sink

AICHE JOURNAL, Issue 8 2010
Yongping Chen
Abstract A three-dimensional thermal and hydrodynamic model for constructal tree-shaped minichannel heat sink is developed. The heat and fluid flow in the constructal heat sink with an inlet hydraulic diameter of 4 mm are numerically analyzed, taking into consideration conjugate heat transfer in the channel walls. The pressure drop, temperature uniformity, and coefficient of performance (COP) of the constructal tree-shaped heat sink are evaluated and compared with those of the corresponding traditional serpentine flow pattern. The results indicate that the constructal tree-shaped minichannel heat sinks have considerable advantages over the traditional serpentine flow patterns in both heat transfer and pressure drop. The strong and weak heat flow can be effectively allocated in tree-shaped flow structures; hence, the inherent advantage of uniform temperature on the heating surface in the constructal tree-shaped heat sink is demonstrated. And in tree-shaped flow structures, the local pressure loss due to confluence flow is found to be larger than that due to diffluence flow. In addition, an aluminum constructal tree-shaped minichannel heat sink is fabricated to conduct the verification experiment. The experimentally measured temperature distribution and pressure drop are in agreement with the numerical simulation, which verifies that the present model is reasonable. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]

Dynamic behavior of the flow field in a RIM machine mixing chamber

AICHE JOURNAL, Issue 6 2009
Ricardo J. Santos
Abstract Dynamic behavior of the flow field in a Reaction Injection Molding, RIM, machine mixing chamber, having dimensions typically used in industrial machines, is studied from dynamic velocity data of Laser Doppler Anemometry, LDA, measurements and Computational Fluid Dynamics, CFD, simulations with a 2D model. This study is based on the spectral analysis of the dynamic flow field data. The typical frequencies, in the reactor flow field, are identified and its values are related to the identified flow structures. The differences between the typical frequencies from experiments and simulations are observed and justified on the basis of the 2D representation of a 3D cylindrical geometry. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Clustering behaviour in gas,liquid,solid circulating fluidized beds with low solid holdups of resin particles

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010
Jianhua Liu
Abstract The flow in a gas,liquid,solid circulating fluidized bed is self-organised and manifests itself with clustering of particles and bubbles. The clustering behaviour in the fluidized bed at low solid holdups of resin particles was experimentally investigated with a high-speed image measurement and treatment technique of complementary metal oxide semiconductor to enhance the fundamental understanding on such a flow. Several new physical quantities were suggested to characterise such ordered flow structures. The main findings are as follows. The clusters of solid particles largely exist as doublets and triplets, the mixed groups of particles and bubbles mostly exist as one bubble carrying two to four particles. Increasing superficial liquid velocity, particle diameter or density weakens the aggregation degrees of both particle and mixed clusters in the riser and downer, except that the increase of superficial liquid velocity enhances the mixed clustering behaviour in the riser. The climbing of the auxiliary liquid velocity or liquid phase viscosity intensifies the aggregation behaviour, except that the increase of liquid phase viscosity reduces the mixed clustering degree in the riser. The influences of superficial gas velocity and surface tension of liquid phase on the clustering behaviour seem to be a little complex and the trends are not simply increasing or decreasing. The life cycle of solid particle clusters in the GLS riser is not sensitive to the operation conditions, being around 0.07,s. The mixed clusters' life cycle is more sensitive to the conditions and physical properties of phases, changing from 0.02 to 0.07,s. L'écoulement dans un lit fluidisé de circulation gaz-liquide-solide s'organise souvent de lui même et se manifeste avec l'agrégation des particules et des bulles. Le comportement de l'agrégation dans le lit fluidisé à faible retenue de particules de résine solide a été étudié expérimentalement en utilisant une technique d'imagerie ultra-rapide de mesure et de traitement à base de semi-conducteur complémentaire à l'oxyde de métal afin d'approfondir la compréhension fondamentale d'un tel écoulement. Plusieurs nouvelles quantités physiques ont été suggérées pour caractériser une telle structure d'écoulement auto-organisé. Les principaux résultats sont comme suit. Les agrégations de particules solides existent principalement en tant que doublets et triplets, les groupes mixtes de particules et de bulles existent pour la plupart sous la forme d'une bulle comportant deux à quatre particules. Une augmentation de la vitesse superficielle du liquide, du diamètre des particules ou de la densité affaiblit à la fois les degrés d'agrégation des particules et des agrégats mixtes dans la colonne montante et dans la colonne descendante, sauf que l'augmentation de la vitesse superficielle du liquide intensifie le comportement d'agrégation mixte dans la colonne montante. L'accroissement de la vitesse auxiliaire du liquide ou de la viscosité de la phase liquide intensifie le comportement d'agrégation, sauf que l'augmentation de la viscosité de la phase liquide réduit le degré d'agrégation mixte dans la colonne montante. Les influences de la vitesse superficielle du gaz et de la tension de surface de la phase liquide sur le comportement de l'agrégation semblent être quelque peu complexes et les tendances ne sont pas simplement croissantes ou décroissantes. Le cycle de vie des agrégats de particules solides dans la colonne gaz-liquide-solide montante n'est pas sensible aux facteurs, tournant autour de 0.07,s. Le cycle de vie des agrégats mixtes est plus sensible aux conditions de fonctionnement et aux caractéristiques physiques des phases, évoluant de 0.02 à 0.07,s. [source]

Measurements of local flow structures of conical spouted beds by optical fibre probes

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2009
Zhiguo Wang
Abstract A new calibration set-up was designed and assembled, and a comprehensive sensitivity analysis was conducted to investigate factors that may affect the calibration of the effective distance of an optical fibre particle velocity probe. It is shown that the glass window has the most significant impact on the calibration result. The optical fibre probe was then applied to measure local particle velocities and solid fractions inside a half and a full circular conical spouted bed. It is found that the overall particle velocity profiles, as well as the shapes of the spout and fountain are quite similar in both columns. Un nouveau réglage d'étalonnage a été conçu et assemblé, et une analyse de sensibilité complète a été effectuée afin d'investiguer les facteurs risquant d'avoir un impact sur l'étalonnage de la distance réelle d'une sonde à fibres optiques de la vitesse des particules. Il a été démontré que la fenêtre de vitre a l'impact le plus important sur les résultats de l'étalonnage. La sonde à fibres optiques a par la suite été utilisée pour mesurer les vitesses locales des particules et des fractions de solide à l'intérieur d'un demi et d'un plein lit jaillissant conique circulaire. Il est démontré que l'ensemble des profils de vitesse des particules, ainsi que la forme du bec et de la fontaine sont très semblables dans les deux colonnes. [source]

Experimental Simulation of the Reactor Section of Fluid Cokers: Comparison of FCC and Fluid Coke Particles

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2006
Xuqi Song
Abstract The hydrodynamics of fluid cokers were studied in a pressurized fully cylindrical cold model of diameter 483 mm, geometrically and dynamically scaled down by a factor of ,20 from commercial units. Differential pressure fluctuations, voidage distributions, solids momentum flux distributions and steady state gas mixing behaviour in the reactor section are compared for the same operating conditions with two kinds of particles, FCC and fluid coke. The voidage distributions and core-annular flow structures in the reactor section were similar enough that either FCC or fluid coke particles can be used for cold modelling of fluid cokers. On a étudié l'hydrodynamique d'unités de cokéfaction fluide dans une maquette froide cylindrique pressurisée de 483 mm de diamètre, géométriquement et dynamiquement réduite d'un facteur 20 par rapport à des unités commerciales. Les fluctuations de pression différentielles, les distributions de vide, les distributions de flux de moment des solides et le comportement de mélange de gaz à l'état stable dans la section du réacteur sont comparés pour les mêmes conditions opératoires avec deux sortes de particules, soient FCC et coke fluide. Les distributions de vide et les structures d'écoulement noyau-espace annulaire dans la section du réacteur sont suffisamment semblables pour que des particules de FCC ou de coke fluide puissent être utilisées pour la modélisation à froid d'unités de cokéfaction fluide. [source]

Sources of water vapour contributing to the Elbe flood in August 2002,A tagging study in a mesoscale model

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 638 2009
H. Sodemann
Abstract In this study we investigate the contribution of various moisture sources to the Elbe flood that occurred in Central Europe during August 2002. An 8-day simulation with the mesoscale numerical weather prediction model CHRM, including newly implemented water vapour tracers, has been performed. According to the simulation, rather than drawing moisture from one single dominant source region, water vapour from widely separated moisture sources contributed to the extreme precipitation in the most affected area, notably at distinct, subsequent periods of time, and each in significant amounts. These moisture sources include the Atlantic and Mediterranean ocean areas inside the model domain, evapotranspiration from land areas, and long-range advection from subtropical areas outside the model domain. The results highlight the importance of the concurrent upper-level circulation and the mesoscale flow structures associated with the cyclone for producing extreme precipitation in parts of Germany, Austria, and the Czech Republic during that period. Furthermore, the numerical and technical problems of implementing water vapour tracers into a limited-area model are discussed, including conservative tracer advection, initialization, boundary treatment, and the handling of precipitation parametrizations. An evaluation of the consistency of the method in terms of water vapour, cloud water, and precipitation is provided, with generally satisfying results. The model with its detailed water vapour tracer implementation can now be used for further case-studies and climatological simulations, and serve as a reference for evaluating the performance of other moisture tracking methods, such as those based on backward trajectories. Copyright © 2009 Royal Meteorological Society [source]