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Vortex
Kinds of Vortex Terms modified by Vortex Selected AbstractsMetapopulation viability of the marsupial Micoureus demerarae in small Atlantic forest fragments in south-eastern BrazilANIMAL CONSERVATION, Issue 3 2000Daniel Brito A population viability analysis (PVA) was carried out for populations of the arboreal didelphid Micoureus demerarae in eight small (1.5,15.0 ha) forest fragments in south-eastern Brazil. Analysis was based on field data obtained through demographic studies carried out since 1995. Populations are small, but connected by dispersing individuals, thus forming a metapopulation. Frequency of catastrophic fires was estimated from the Reserve's historical records. We used the computer package VORTEX for all analyses. All populations and the metapopulation were found to be endangered within 100 years (extinction probability > 0.98). A sensitivity analysis was run varying six parameters: three demographic (sex ratio, migration and mortality rates), two environmental (K, fire frequency) and one genetic (level of inbreeding depression). Genetics, K, mortality rates and sex ratio seemed to play major roles to population persistence, whereas catastrophes and migration rates had a secondary role. Among demographic factors, extinction rate was least sensitive to migration rate. Micoureus demerarae can be used as a model species, thus improving our knowledge of how extinction-prone populations of neotropical arboreal marsupials in forest fragments might be, and which management actions could decrease such risks. [source] VorteX , Enhancing the pedagogy in software development educationPROCEEDINGS OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE & TECHNOLOGY (ELECTRONIC), Issue 1 2003Mark Ridgway VorteX is a new product, pedagogically biased in its support for assisting and managing collaborative projects. Currently targeted at a software development environment, a joint venture between Khaydor Ltd and the University of Wales, Aberystwyth, VorteX will soon be more generally applicable. Through the use of collaboration, students are able to gain deeper knowledge and understanding of their work. Unfortunately, group projects are notoriously difficult to grade due to the lack of individual accountability. VorteX overcomes this problem by tracking developments of the group work, generating metrics and providing animation facilities to replay the activities undertaken. [source] Vortexes and Nanoscale Chirality,ANGEWANDTE CHEMIE, Issue 1 2010Alessandro D'Urso Dr. J-Aggregate antworten dynamisch auf durch Rühren erzeugte Strudel. Das CD-Signal kehrt sich mit der Rührrichtung um, und seine Intensität nimmt zu. Bei längerem Rühren lagern sich chirale Aggregate an der Küvettenwand ab, deren Chiraliät von der Rührrichtung abhängt. Das Rühren verschiebt das Gleichgewicht einer racemischen Mischung zu der durch die Rührrichtung gewählten (und bevorzugten) Seite (siehe Bild; CW,CCW: Rühren im bzw. gegen den Uhrzeiger). [source] Hochtemperatur-Supraflüssigkeit in ultrakaltem Fermi-GasPHYSIK IN UNSERER ZEIT (PHIUZ), Issue 5 2005Martin Zwierlein Ultrakalte atomare Gase, eine Million mal dünner als Luft, bieten die faszinierende Möglichkeit, das Phänomen der Supraflüssigkeit in seiner Reinstform zu beobachten. Bisher ist dies nur für Gase aus Bosonen, Teilchen mit ganzzahligem Spin, gelungen. Nun wurde auch in einem rotierenden Gas aus Fermionen, Teilchen mit halbzahligem Spin, der Nachweis für Supraflüssigkeit erbracht: Es gelang die Beobachtung regelmäßig angeordneter Vortices [1]. Diese neue Form der Supraflüssigkeit würde, skaliert auf die Dichte von Elektronen im Festkörper, bereits oberhalb der Zimmertemperatur eintreten. [source] A Test of Wills: Jimmy Carter, South Africa, and the Independence of NamibiaDIPLOMATIC HISTORY, Issue 5 2010Piero Gleijeses Until 1975, Washington paid little attention to southern Africa, a backwater in the Cold War where weak insurgencies posed little threat to white rule in Angola, Mozambique, Rhodesia, and Namibia. The collapse of the Portuguese dictatorship in April 1974 meant the end of white rule in Angola and Mozambique. The Cuban victory in Angola the following year propelled southern Africa into the vortex of the Cold War. Between 1977 and 1981, the Carter administration engaged in a complicated minuet with South Africa and the Namibian rebels to craft a negotiated settlement that would grant Namibia its independence. Secretary of State Cyrus Vance and National Security Adviser Zbigniew Brzezinski clashed over the course the United States should follow, while Cuba and the Soviet Union strongly supported the Namibian insurgents and 20,000 Cuban soldiers were poised in neighboring Angola. I analyze the failure of Carter's Namibia policy based on US, Cuban and South African documents, as well as interviews with Namibian, US, Cuban and South African protagonists. [source] The linkage between velocity patterns and sediment entrainment in a forced-pool and riffle unitEARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2009D. M. Thompson Abstract A field-based project was initiated in order to characterize velocities and sediment entrainment in a forced-pool and riffle sequence. Three-dimensional velocities and turbulence intensities were measured with an acoustic Doppler velocimeter at 222 different points at three similar flows that averaged approximately 4·35 m3 s,1 within a large pool,riffle unit on North Saint Vrain Creek, Colorado. Sediment-sorting patterns were observed with the introduction of 500 tracer particles painted according to initial seeding location. Tracer particles moved sporadically during a 113 day period in response to the annual snowmelt peak flow, which reached a maximum level of 14·8 m3 s,1. Velocity data indicate high instantaneous velocities and turbulence levels in the centre of pools. Patterns of sediment deposition support the notion that stream competence is higher in the pool than the downstream riffle. Flow convergence around a large channel constriction appears to play a major role in multiple processes that include helical flow development and sediment routing, and backwater development with low velocities and turbulence levels above the constriction that may locally limit sediment supply. Jet flow, flow separation, vortex scour and turbulence generation enhance scour in the centre of pools. Ultimately, multiple processes appear to play some role in maintenance of this forced pool and the associated riffle. Copyright © 2008 John Wiley & Sons, Ltd. [source] Analysis of hepatic vitamins A1, A2, their fatty acyl esters, and vitamin E for biomonitoring mammals feeding on freshwater fishENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2002Anne Käkelä Abstract In tissues of freshwater fish,feeding mammals, 3,4-didehydroretinol (A2) is a major form of vitamin A. In mink liver, with organochlorine exposure, this analog has been found to decrease more than retinol (A1) and thus has potential as a sensitive freshwater biomarker. The presence of the analogs A1 and A2 as alcohol and different fatty acyl esters, which react to polychlorinated biphenyls differently, necessitates detailed analyses achieved by using direct extraction of tissue homogenate. In direct hexane extraction, compared to total levels of the vitamins obtained in the saponification procedure, a large proportion of the vitamins was released only after repeated and long-time vortex mixing with the extraction solvent. Thus, in tissue extraction, the use of internal standardization alone can lead to a rough underestimation of the levels of these fat-soluble vitamins. For analyses of vitamins A1 and A2 in liver, we applied the argentation high-performance liquid chromatography, which provided good separation of individual A1 and A2 fatty acyl esters. We report retention times for numerous esters of A1 and A2 and, to aid identification, the change in their retention properties after adding AgNO3 to the mobile phase. The argentation did not affect the recoveries of any forms of the retinoids studied but destroyed half the vitamin E. Despite selective acylation of fatty acids into the vitamin A esters, the fatty acids of the esters were the same as those found to be the major fatty acids in the gas,liquid chromatography of total lipids. The goal of this work was to create a methodology that is suitable for biomonitoring alcoholic and esterified vitamins A1 and A2 in tissues of freshwater fish,feeding mammals. [source] A spatially advancing turbulent flow and heat transfer in a curved channelHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2010Koji Matsubara Abstract Direct numerical simulation was performed for a spatially advancing turbulent flow and heat transfer in a two-dimensional curved channel, where one wall was heated to a constant temperature and the other wall was cooled to a different constant temperature. In the simulation, fully developed flow and temperature from the straight-channel driver was passed through the inlet of the curved-channel domain. The frictional Reynolds number was assigned 150, and the Prandtl number was given 0.71. Since the flow field was examined in the previous paper, the thermal features are mainly targeted in this paper. The turbulent heat flux showed trends consistent with a growing process of large-scale vortices. In the curved part, the wall-normal component of the turbulent heat flux was twice as large as the counterpart in the straight part, suggesting active heat transport of large-scale vortices. In the inner side of the same section, temperature fluctuation was abnormally large compared with the modest fluctuation of the wall-normal velocity. This was caused by the combined effect of the large-scale motion of the vortices and the wide variation of the mean temperature; in such a temperature distribution, large-scale ejection of the hot fluid near the outer wall, which is transported into the near inner-wall region, should have a large impact on the thermal boundary layer near the inner wall. Wave number decomposition was conducted for various statistics, which showed that the contribution of the large-scale vortex to the total turbulent heat flux normal to the wall reached roughly 80% inside the channel 135° downstream from the curved-channel inlet. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20275 [source] Numerical analysis of the effect of boundary layer thickness on vortex structures and heat transfer in the wake behind a hillHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 7 2009Hideki Yanaoka Abstract This study presents a three-dimensional numerical analysis of the effect of boundary layer thickness on vortex structures and heat transfer behind a hill mounted in a laminar boundary layer. When the thickness of the velocity boundary layer is comparable to the hill height, a hairpin vortex is formed symmetrically to the center of the spanwise direction in the wake. A secondary vortex is formed between the legs, and horn-shaped secondary vortices appear under the concave parts of the hairpin vortex. When the boundary layer thickness increases, the legs and horn-shaped secondary vortices move toward the center of the spanwise direction, and thus heat transport and heat transfer increase there. At this time, high-turbulence areas generated locally move toward the center of the spanwise direction with an increase in the boundary layer thickness. With a further increase in the boundary layer thickness, steady streamwise vortices are formed downstream of the hill, but the heat transfer decreases. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20261 [source] Numerical simulation of asymmetrical flow and heat transfer behind a hill in shear flowsHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 8 2008Hideki Yanaoka Abstract Three-dimensional numerical simulations of asymmetrical flows and heat transfer around a hill in shear flows were performed. When shear velocity distributions are introduced at the inlet, a vortex pair is formed asymmetrically to the spanwise direction behind the hill. Further, an asymmetrical hairpin vortex is periodically generated downstream. The leg of the asymmetrical hairpin vortex on the high-speed side collapses first. Further downstream, the asymmetrical hairpin vortex breaks down earlier than the symmetrical hairpin vortex, and streamwise vortices appear on the high-speed side. These streamwise vortices increase the heat transfer downstream. In contrast, no hairpin vortex appears in the case of a strong shear velocity distribution, but instead a streamwise vortex appears. The heat transfer decreases downstream since the turbulence generated by streamwise vortices is weak. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20223 [source] Numerical simulation of natural convection heat transfer in the open space between two horizontal circular planesHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 6 2001Hideki Tokanai Abstract Numerical simulations were conducted for natural convection heat transfer in a narrow gap between two horizontal plates in air. The lower plate is an infinite plate with a circular heating zone. The upper one is the bottom of a vertical cylinder, which is placed right above the circular heated plate and kept at room temperature. A set of Navier,Stokes equations and an energy equation are analyzed for a variety of combinations of gap clearance and Rayleigh number. The calculated average heat transfer values are shown to be in good agreement with the experimentally obtained ones reported in a previous paper. From the obtained isotherms, streamlines, and local Nusselt numbers, it is found that two types of convection appear in the gap space according to the conditions of Rayleigh number and gap clearance: one is a simple convection due to a single renewal flow which replaces heated air with ambient air and the other is a combined convection due to several vortex flows and a renewal flow. Furthermore, the flow rate of each flow controls the rate of heat transfer from the limited area which is covered by each flow. From this fact, the validity of the previously proposed heat transfer correlation is briefly discussed. © 2001 Scripta Technica, Heat Trans Asian Res, 30(6): 485,502, 2001 [source] Numerical study of lid-driven flow in orthogonal and skewed porous cavityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 10 2008D. Jaya Krishna Abstract Effects of Reynolds number, Darcy number, porosity, aspect ratio and skewness are studied in detail for lid-driven cavity flows filled with fluid-saturated porous medium. A generalized non-Darcy approach has been considered to account for linear and non-linear drag forces. The governing equations are solved by using finite volume method. A quadrilateral cell in a semi-staggered arrangement has been employed and is transformed into a standard square element using local body-fitting co-ordinates by co-ordinate transformation. Details of the flow physics reveal that by the reduction of Darcy number, the primary vortex becomes weaker and tends to move towards the lid. As a measure of volume flow rate maximum stream function value is considered. It is found that, with the reduction in Darcy number and with the increase in Reynolds number and skewness the maximum stream function value reduces. Copyright © 2007 John Wiley & Sons, Ltd. [source] Multiple-relaxation-time lattice Boltzmann computation of channel flow past a square cylinder with an upstream control bi-partitionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2010M. A. Moussaoui Abstract The present paper deals with the application of the multiple-relaxation-time lattice Boltzmann equation (MRT-LBE) for the simulation of a channel flow with a bi-partition located upstream of a square cylinder in order to control the flow. Numerical investigations have been carried out for different heights and positions of the bi-partition at Reynolds number of 250. Key computational issues involved are the computation of fluid forces acting on the square cylinder, the vortex shedding frequency and the impact of such bluff body on the flow pattern. A particular attention is paid to drag and lift coefficients on the square cylinder. The predicted results from MRT-LBE simulations show that in most cases, the interaction was beneficial insofar as the drag of the square block was lower with the bi-partition than without it. Fluctuating side forces due to vortex shedding from the main body were also reduced for most bi-partition positions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Direct numerical simulation of low Reynolds number flows in an open-channel with sidewallsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2010Younghoon Joung Abstract A direct numerical simulation of low Reynolds number turbulent flows in an open-channel with sidewalls is presented. Mean flow and turbulence structures are described and compared with both simulated and measured data available from the literature. The simulation results show that secondary flows are generated near the walls and free surface. In particular, at the upper corner of the channel, a small vortex called inner secondary flows is simulated. The results show that the inner secondary flows, counter-rotating to outer secondary flows away from the sidewall, increase the shear velocity near the free surface. The secondary flows observed in turbulent open-channel flows are related to the production of Reynolds shear stress. A quadrant analysis shows that sweeps and ejections are dominant in the regions where secondary flows rush in toward the wall and eject from the wall, respectively. A conditional quadrant analysis also reveals that the production of Reynolds shear stress and the secondary flow patterns are determined by the directional tendency of the dominant coherent structures. Copyright © 2009 John Wiley & Sons, Ltd. [source] Nonreflecting boundary conditions based on nonlinear multidimensional characteristicsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2010Qianlong Liu Abstract Nonlinear characteristic boundary conditions based on nonlinear multidimensional characteristics are proposed for 2- and 3-D compressible Navier,Stokes equations with/without scalar transport equations. This approach is consistent with the flow physics and transport properties. Based on the theory of characteristics, which is a rigorous mathematical technique, multidimensional flows can be decomposed into acoustic, entropy, and vorticity waves. Nonreflecting boundary conditions are derived by setting corresponding characteristic variables of incoming waves to zero and by partially damping the source terms of the incoming acoustic waves. In order to obtain the resulting optimal damping coefficient, analysis is performed for problems of pure acoustic plane wave propagation and arbitrary flows. The proposed boundary conditions are tested on two benchmark problems: cylindrical acoustic wave propagation and the wake flow behind a cylinder with strong periodic vortex convected out of the computational domain. This new approach substantially minimizes the spurious wave reflections of pressure, density, temperature, and velocity as well as vorticity from the artificial boundaries, where strong multidimensional flow effects exist. The numerical simulations yield accurate results, confirm the optimal damping coefficient obtained from analysis, and verify that the method substantially improves the 1-D characteristics-based nonreflecting boundary conditions for complex multidimensional flows. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effect of magnetic Reynolds number on the two-dimensional hydromagnetic flow around a cylinderINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2009T. V. S. Sekhar Abstract Numerical experiments have been conducted to study the effect of magnetic Reynolds number on the steady, two-dimensional, viscous, incompressible and electrically conducting flow around a circular cylinder. Besides usual Reynolds number Re, the flow is governed by the magnetic Reynolds number Rm and Alfvén number ,. The flow and magnetic field are uniform and parallel at large distances from the cylinder. The pressure Poisson equation is solved to find the pressure fields in the entire flow region. The effects of the magnetic field and electrical conductivity on the recirculation bubble, drag coefficient, standing vortex and pressure are presented and discussed. For low interaction parameter (N<1), the suppression of the flow-separation is nearly independent of the conductivity of the fluid, whereas for large interaction parameters, the conductivity of the fluid strongly influences the control of flow-separation. Copyright © 2008 John Wiley & Sons, Ltd. [source] BILU implicit multiblock Euler/Navier,Stokes simulation for rotor tip vortex and wake convectionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2007Bowen Zhong Abstract In this paper, a block incomplete lower,upper (BILU) decomposition method is incorporated with a multiblock three-dimensional Euler/Navier,Stokes solver for simulation of hovering rotor tip vortices and rotor wake convection. Results of both Euler and Navier,Stokes simulations are obtained and compared with experimental observations. The comparisons include surface pressure distributions and tip vortex trajectories. The comparisons suggest that resolution of the boundary layer is important for the accurate evaluation of the blade surface loading, but is less so for the correct prediction of the vortex trajectory. Numerical tests show that, using Courant,Friedrichs,Lewy (CFL) number of 10 or 30 with the developed BILU implicit scheme can be 6,7 times faster than an explicit scheme. The importance of solution acceleration schemes that increase the permitted time-step is illustrated by comparing the evolving wake structures at different stages of the calculation. In contrast to fixed wing simulations, the extent of the wake structures is shown to require resolution of large physical time. This observation explains the poor performance that is obtained when employing convergence acceleration strategies originally intended for solution of equilibrium problems, such as the multigrid methods. Copyright © 2007 John Wiley & Sons, Ltd. [source] Numerical simulation of flapping-wing insect hovering flight at unsteady flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2007Decan Zuo Abstract A computational fluid dynamics (CFD) analysis was conducted to study the unsteady aerodynamics of a virtual flying bumblebee during hovering flight. The integrated geometry of bumblebee was established to define the shape of a three-dimensional virtual bumblebee model with beating its wings, accurately mimicking the three-dimensional movements of wings during hovering flight. The kinematics data of wings documented from the measurement to the bumblebee in normal hovering flight aided by the high-speed video. The Navier,Stokes equations are solved numerically. The solution provides the flow and pressure fields, from which the aerodynamic forces and vorticity wake structure are obtained. Insights into the unsteady aerodynamic force generation process are gained from the force and flow-structure information. The CFD analysis has established an overall understanding of the viscous and unsteady flow around the virtual flying bumblebee and of the time course of instantaneous force production, which reveals that hovering flight is dominated by the unsteady aerodynamics of both the instantaneous dynamics and also the past history of the wing. A coherent leading-edge vortex with axial flow and the attached wingtip vortex and trailing edge vortex were detected. The leading edge vortex, wing tip vortex and trailing edge vortex, which caused by the pressure difference between the upper and the lower surface of wings. The axial flow, which include the spanwise flow and chordwise flow, is derived from the spanwise pressure gradient and chordwise pressure gradient, will stabilize the vortex and gives it a characteristic spiral conical shape. Copyright © 2006 John Wiley & Sons, Ltd. [source] Finite volume method with zonal-embedded grids for cylindrical coordinatesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2006Yong Kweon Suh Abstract A zonal-embedded-grid technique has been developed for computation of the two-dimensional Navier,Stokes equations with cylindrical coordinates. As is well known, the conventional regular grid system gives very small grid spacings in the azimuthal direction so it requires a very small time step for a stable numerical solution when the explicit method is used. The fundamental idea of the zonal-embedded-grid technique is that the number of azimuthal grids can be made small near the origin of the coordinates so that the grid size is more uniformly distributed over the domain than with the conventional regular-grid system. The code developed using this technique combined with the explicit, finite-volume method was then applied to calculation of the asymmetric swirl flows and Lamb's multi-polar vortex flows within a full circle and the spin-up flows within a semi-circle. It was shown that the zonal-embedded grids allow a time step far larger than the conventional regular grids. For the case of the Lamb's multi-polar vortex flows, the code was validated by comparing the calculated results with the exact solutions. For the case of the semi-circle spin-up flows, the experimental results were used for the verification. It was seen that the numerical results were in good agreement with the experimental results both qualitatively and quantitatively. Copyright © 2006 John Wiley & Sons, Ltd. [source] A combined vortex and panel method for numerical simulations of viscous flows: a comparative study of a vortex particle method and a finite volume methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10 2005Kwang-Soo Kim Abstract This paper describes and compares two vorticity-based integral approaches for the solution of the incompressible Navier,Stokes equations. Either a Lagrangian vortex particle method or an Eulerian finite volume scheme is implemented to solve the vorticity transport equation with a vorticity boundary condition. The Biot,Savart integral is used to compute the velocity field from a vorticity distribution over a fluid domain. The vorticity boundary condition is improved by the use of an iteration scheme connected with the well-established panel method. In the early stages of development of flows around an impulsively started circular cylinder, and past an impulsively started foil with varying angles of attack, the computational results obtained by the Lagrangian vortex method are compared with those obtained by the Eulerian finite volume method. The comparison is performed separately for the pressure fields as well. The results obtained by the two methods are in good agreement, and give a better understanding of the vorticity-based methods. Copyright © 2005 John Wiley & Sons, Ltd. [source] A level set characteristic Galerkin finite element method for free surface flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2005Ching-Long Lin Abstract This paper presents a numerical method for free surface flows that couples the incompressible Navier,Stokes equations with the level set method in the finite element framework. The implicit characteristic-Galerkin approximation together with the fractional four-step algorithm is employed to discretize the governing equations. The schemes for solving the level set evolution and reinitialization equations are verified with several benchmark cases, including stationary circle, rotation of a slotted disk and stretching of a circular fluid element. The results are compared with those calculated from the level set finite volume method of Yue et al. (Int. J. Numer. Methods Fluids 2003; 42:853,884), which employed the third-order essentially non-oscillatory (ENO) schemes for advection of the level set function in a generalized curvilinear coordinate system. The comparison indicates that the characteristic Galerkin approximation of the level set equations yields more accurate solutions. The second-order accuracy of the Navier,Stokes solver is confirmed by simulation of decay vortex. The coupled system of the Navier,Stokes and level set equations then is validated by solitary wave and broken dam problems. The simulation results are in excellent agreement with experimental data. Copyright © 2005 John Wiley & Sons, Ltd. [source] A nonlinear atomization model for computation of drop size distributions and spray simulationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2005Hongbok Park Abstract A model has been developed to provide a comprehensive simulation of a spray formed by a high-speed liquid jet. The primary atomization process is simulated in a completely nonlinear fashion using the boundary element method under the assumption of axisymmetric, inviscid flow. The presence of the orifice boundary layer is simulated with a ring vortex whose strength and location are uniquely determined from boundary layer properties at the orifice exit plane. Droplet and axisymmetric ligament tracking models have been developed to provide more comprehensive spray simulations. The breakup of the axisymmetric ligaments shed from the parent surface is assessed both in a nonlinear fashion as well as using the linear stability analysis of Ponstein. Using this latter approach, drop size distributions have been generated from first principles and compared with the popular Rosin,Rammler model. Copyright © 2005 John Wiley & Sons, Ltd. [source] Numerical solutions of 2-D steady incompressible driven cavity flow at high Reynolds numbersINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2005E. Erturk Abstract Numerical calculations of the 2-D steady incompressible driven cavity flow are presented. The Navier,Stokes equations in streamfunction and vorticity formulation are solved numerically using a fine uniform grid mesh of 601 × 601. The steady driven cavity flow solutions are computed for Re , 21 000 with a maximum absolute residuals of the governing equations that were less than 10,10. A new quaternary vortex at the bottom left corner and a new tertiary vortex at the top left corner of the cavity are observed in the flow field as the Reynolds number increases. Detailed results are presented and comparisons are made with benchmark solutions found in the literature. Copyright © 2005 John Wiley & Sons, Ltd. [source] Adaptive strategy of the supersonic turbulent flow over a backward-facing stepINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2004Shih-Ying YangArticle first published online: 16 MAR 200 Abstract An adaptive strategy incorporating mesh remeshing and refining is developed to study the supersonic turbulent flow over a backward-facing step on a mixed quadrilateral,triangular mesh. In the Cartesian co-ordinate system, the unsteady Favre-averaged Navier,Stokes equations with a low-Reynolds-number k,,turbulence model are solved using a locally implicit scheme with an anisotropic dissipation model. In the present adaptive strategy, two error indicators for both mesh remeshing and refining, respectively, are presented. The remeshing error indicator incorporates unified magnitude of substantial derivative of pressure and that of vorticity magnitude, whereas the refining error indicator incorporates unified magnitude of substantial derivative of pressure and that of weighted vorticity magnitude. To assess the present approach, the transonic turbulent flow around an NACA 0012 airfoil is performed. Based on the comparison with the experimental data, the accuracy of the present approach is confirmed. According to the high-resolutional result on the adaptive mesh, the structure of backstep corner vortex, expansion wave and oblique shock wave is distinctly captured. Copyright © 2004 John Wiley & Sons, Ltd. [source] Development of an optimal hybrid finite volume/element method for viscoelastic flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2003M. Aboubacar Abstract A cell-vertex hybrid finite volume/element method is investigated that is implemented on triangles and applied to the numerical solution of Oldroyd model fluids in contraction flows. Particular attention is paid to establishing high-order accuracy, whilst retaining favourable stability properties. Elevated levels of elasticity are sought. The main impact of this study reveals that switching from quadratic to linear finite volume stress representation with discontinuous stress gradients, and incorporating local reduced quadrature at the re-entrant corner, provide enhance stability properties. Solution smoothness is achieved by adopting the non-conservative flux form with area integration, by appealing to quadratic recovered velocity-gradients, and through consistency considerations in the treatment of the time term in the constitutive equation. In this manner, high-order accuracy is maintained, stability is ensured, and the finer features of the flow are confirmed via mesh refinement. Lip vortices are observed for We>1, and a trailing-edge vortex is also apparent. Loss of evolution and solution asymptotic behaviour towards the re-entrant corner are also discussed. Copyright © 2003 John Wiley & Sons, Ltd. [source] Finite element analysis of vortex shedding using equal order interpolationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2002Y. J. Jan Abstract An operator splitting and element-by-element conjugated gradient solver, and equal order interpolations are applied for solving time dependent Navier,Stokes (NS) equations to simulate flow induced vortex shedding in the present study. In addition, the convection term is corrected by balanced tensor diffusivity, which can stabilize the numerical simulation and overcome the numerical oscillations. The evolution of the interested flowing properties with time is analyzed by using spectral analysis. The developed code has been validated by the application of two examples: a driven cavity flow and a flow induced vortex vibration. Results from the first example for Reynolds number Re=103 and Re=104 are compared with other numerical simulations. Results from the second example, uniform flow past a square rod over a wide range of high Reynolds numbers from Re=103,105, are compared with experimental data and other numerical studies. Copyright © 2002 John Wiley & Sons, Ltd. [source] A numerical study of an unsteady laminar flow in a doubly constricted 3D vesselINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2002B. V. Rathish Kumar Abstract Unsteady flow dynamics in doubly constricted 3D vessels have been investigated under pulsatile flow conditions for a full cycle of period T. The coupled non-linear partial differential equations governing the mass and momentum of a viscous incompressible fluid has been numerically analyzed by a time accurate Finite Volume Scheme in an implicit Euler time marching setting. Roe's flux difference splitting of non-linear terms and the pseudo-compressibility technique employed in the current numerical scheme makes it robust both in space and time. Computational experiments are carried out to assess the influence of Reynolds' number and the spacing between two mild constrictions on the pressure drop across the constrictions. The study reveals that the pressure drop across a series of mild constrictions can get physiologically critical and is also found to be sensitive both to the spacing between the constrictions and the oscillatory nature of the inflow profile. The flow separation zone on the downstream constriction is seen to detach from the diverging wall of the constriction leading to vortex shedding with 3D features earlier than that on the wall in the spacing between the two constrictions. Copyright © 2002 John Wiley & Sons, Ltd. [source] Transition from vortex to wall driven turbulence production in the Taylor,Couette system with a rotating inner cylinderINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2002W. M. J. Batten Abstract Axisymmetrically stable turbulent Taylor vortices between two concentric cylinders are studied with respect to the transition from vortex to wall driven turbulent production. The outer cylinder is stationary and the inner cylinder rotates. A low Reynolds number turbulence model using the k - , formulation, facilitates an analysis of the velocity gradients in the Taylor,Couette flow. For a fixed inner radius, three radius ratios 0.734, 0.941 and 0.985 are employed to identify the Reynolds number range at which this transition occurs. At relatively low Reynolds numbers, turbulent production is shown to be dominated by the outflowing boundary of the Taylor vortex. As the Reynolds number increases, shear driven turbulence (due to the rotating cylinder) becomes the dominating factor. For relatively small gaps turbulent flow is shown to occur at Taylor numbers lower than previously reported. Copyright © 2002 John Wiley & Sons, Ltd. [source] Suppression of vortex shedding for flow around a circular cylinder using optimal controlINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2002C. Homescu Abstract Adjoint formulation is employed for the optimal control of flow around a rotating cylinder, governed by the unsteady Navier,Stokes equations. The main objective consists of suppressing Karman vortex shedding in the wake of the cylinder by controlling the angular velocity of the rotating body, which can be constant in time or time-dependent. Since the numerical control problem is ill-posed, regularization is employed. An empirical logarithmic law relating the regularization coefficient to the Reynolds number was derived for 60,Re,140. Optimal values of the angular velocity of the cylinder are obtained for Reynolds numbers ranging from Re=60 to Re=1000. The results obtained by the computational optimal control method agree with previously obtained experimental and numerical observations. A significant reduction of the amplitude of the variation of the drag coefficient is obtained for the optimized values of the rotation rate. Copyright © 2002 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] | ||||||||||||||||||||||||||||||||||