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Predicting numerically the large increases in extra pressure drop when boger fluids flow through

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Natural Science 2010年第1期2卷 1-11页

作者： H. R. Tamaddon-Jahromi M. F. Webster K. Walters 不详

Recent numerical studies on pressure-drops in contraction flows have introduced a variety of constitutive models to compare and contrast the competing influences of extensional vis-cosity, normal stress and shear-thinning. Early work on pressure-drops employed the constant viscosity Oldroyd-B and Upper Convected Max- well (UCM) models to represent the behavior of so-called Boger fluids in axisymmetric contrac-tion flows, in (unsuccessful) attempts to predict the very large enhancements that were ob-served experimentally. In more recent studies, other constitutive models have been employed to interpret observed behavior and some pro-gress has been made, although finding a (re-spectable) model to describe observed contrac-tion-flow behavior, even qualitatively, has been frustratingly difficult. With this in mind, the present study discusses the ability of a well- known FENE type model (the so-called FENE- CR model) to describe observed behavior. For various reasons, an axisymmetric (4:1:4) con-traction/expansion geometry, with rounded corners, is singled out for special attention, and a new hybrid finite element/volume algo-rithm is utilized to conduct the modeling, which reflects an incremental pressure-correction time-stepping structure. New to this algo-rithmic formulation are techniques in time discretization, discrete treatment of pressure terms, and compatible stress/velocity-gradient representation. We shall argue that the current simulations for the FENE-CR model have re-sulted in a major improvement in the sort-for agreement between theory and experiment in this important bench-mark problem.

关键词： Contraction flows Extra Pressure Drop Numerical Simulation Extensional Viscosity Normal Stress Differences

Effects of Noncircular Inlet on the Flow Structures in Turbulent Jets

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Journal of Applied Mathematics and Physics 2013年第6期1卷 37-42页

作者： Won Hyun Kim Tae Seon Park School of Mechanical Engineering Kyungpook National University Daegu South Korea

Turbulent jet flows with noncircular nozzle inlet are investigated by using a Reynolds Stress Model. In order to analyze the effects of noncircular inlet, the cross section of inlet are selected as circular, square, and equilateral triangular shape. The jet half-width, vorticity thickness, and developments of the secondary flow are presented. From the result, it is confirmed that the secondary flows of square and equilateral triangular nozzle are more vigorous than that of the circular jet. This development of secondary flows is closely related to the variations of vortical motions in axial and azimuthal directions.

关键词： Noncircular Turbulent Jet Jet Half-Width Vorticity Thickness Secondary flows

Hall Current Effects on Unsteady MHD Flow in a Rotating Parallel Plate Channel Bound-ed by Porous Bed on the Lower Half—Darcy Lapwood Model

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Open Journal of Fluid Dynamics 2015年第4期5卷 275-294页

作者： M. Veera Krishna Jagdish Prakash Department of Mathematics Rayalaseema University Kurnool India Department of Mathematics University of Botswana Gaborone Botswana

We discussed the unsteady flow of an incompressible viscous fluid in a rotating parallel plate channel bounded on one side by a porous bed under the influence of a uniform transverse magnetic field taking hall current into account. The perturbations are created by a constant pressure gradient along the plates in addition to the non-torsional oscillations of the upper plate. The flow in the clean fluid region is governed by Navier-Stoke’s equations while in the porous bed the equations are based on Darcy-Lapwood model. The exact solutions of velocity in the clean fluid and the porous medium consist of steady state and transient state. The time required for the transient state to decay is evaluated in detail and ultimate quasi-steady state solution has been derived analytically and also its behaviour is computationally discussed with reference to different flow parameters. The shear stresses on the boundaries and the mass flux are also obtained analytically and their behaviour is computationally discussed.

关键词： Darcy Lapwood Model Hall Effects MHD flows Porous Bed Unsteady flows and Rotating Parallel Plate Channels

Kolmogorov Flow: Seven Decades of History

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Journal of Applied Mathematics and Physics 2018年第11期6卷 2227-2263页

作者： Emmanouil D. Fylladitakis Electrical & Electronic Engineering Department Faculty of Engineering University of West Attica Athens Greece

The Kolmogorov flow (k-flow) is generated by a stationary sinusoidal force that varies in space. This flow is rather academic since generating such a periodic forcing in an unbounded flow is difficult to appear in nature. Nevertheless, it allows for simple experimental measurements and for a fairly detailed analytical treatment. Although simple, the k-flow makes a good test case for investigating simultaneously inhomogeneous, sheared, and anisotropic features in a flow, and several studies concerning the stability, transition, and turbulence of the k-flow have been published. The present article reviews the most important published works incorporating the k-flow as a test-bed for studying fluid mechanics, testing numerical or experimental methods, or even studying the properties of the k-flow itself.

关键词： Kolmogorov Flow Magnetohydrodynamics Two-Dimensional flows Review

Global Steady Prandtl Expansion over a Moving Boundary Ⅱ

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Peking Mathematical Journal 2019年第3期2卷 353-437页

作者： Sameer Iyer Department of Mathematics Princeton UniversityFine HallPrincetonNJ 08544USA

This is the second paper in a three-part sequence in which we prove that steady,incompressible Navier-Stokes flows posed over the moving boundary,y=0,can be decomposed into Euler and Prandtl flows in the inviscid limit globally in[1,∞)×[0,∞),assuming a sufficiently small velocity *** this paper,we develop a functional framework to capture precise decay rates of the remainders,and prove the corresponding embedding theorems by establishing weighted estimates for their higher order tangential *** tools are then used in conjunction with a third-order energy analysis,which,in particular,enables us to control the nonlinearity vuy globally,leading to the main a priori estimate in the analysis.

关键词： globally flows estimates

Metropolis or City?Metropoles and Cities with Their Citizens

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Journal of Civil Engineering and Architecture 2019年第1期13卷 16-22页

作者： Christian Sallenave Research Laboratory GRECCAU(Groupement de Recherches sur l’Environnement la Conception et le Confort Architectural et Urbain)ENSAP BordeauxTalence 33405France

Through the specific examples of two very different metropoles,not compared but evoked,New York City and Bordeaux Métropole,since globalization from mid-19th and to the beginning of the 21st century,we can observe how metropolitan flows acceleration change cities and citizens *** can we achieve metropolization and globalization of our cities?

关键词： Town city metropoles metropolization globalization flows acceleration urban sprawl melting pot works crossbreeding civil engineering and architecture plural and singular metropolitan space-time

Effects of Rotation on Turbulence Production

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Journal of Applied Mathematics and Physics 2019年第2期7卷 298-330页

作者： Alan S. Hsieh Sedat Biringen Ann and H.J. Smead Department of Aerospace Engineering Sciences University of Colorado Boulder CO USA

Direct numerical simulations (DNS) of non-rotating and rotating turbulent channel flow were conducted. The data base obtained from these DNS simulations was used to investigate the prominent coherent structures involved in the turbulence generation cycle. Predictions from three theoretical models concerning the formation and evolution of sublayer streaks, three-dimensional hairpin vortices and propagating plane waves were validated using visualizations from the present DNS data. Quadrant analysis was used to determine a phase shift between the fluctuating streamwise and wall-normal velocities as a characteristic of turbulence production in the suction region at a low rotation number.

关键词： Direct Numerical Simulation Rotating Turbulent flows Turbulence Structures

Assessing the Hydrological Conditions of the Usangu Wetlands in Tanzania

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Journal of Water Resource and Protection 2011年第12期3卷 876-882页

作者： Shadrack Mwakalila 不详

Although wetlands make up less than 10% of Tanzania, their “critical, life support, ecosystem services” sustain over 95% of lives, of wildlife and of livestock. They provide security as sources of food, water, energy, economy and livelihoods, therefore, the aim of this paper is to address the current hydrologic conditions of Usangu wetlands. Several approaches were used in the collection of data for analysis. Both primary and sec- ondary data was collected and analysed. The key finding shows that, the overall area of the Usangu Wetlands is divided into two main portions, the Eastern Wetland and the Western Wetland, the core wetland, the Ihefu Swamp varies between 30 and 65 km2, whereas the seasonally wetted areas varies between 260 and 1800 km2. Major perennial rivers which feed the Ihefu swamp in Usangu wetlands include Kimani, Mbalali, Ndembera and the Great Ruaha River. The contribution from Mbalali River ranges between 69.17% and 47.78%;from Ndembera River ranges between 25% and 13.83%;from Kimani River ranges between 25% and 8.33% and from Great Ruaha River contribution ranges 24.0% and 2.96%. The irrigated agriculture is most important as a user of water and impacts most heavily on wetlands. Abstraction of water for agriculture is leading to dried up rivers, falling ground water tables, salinated soil and polluted waterways.

关键词： River flows Usangu Wetlands Irrigation Great Ruaha River

A Characteristics-Mix Stabilized Finite Element Method for Variable Density Incompressible Navier-Stokes Equations

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Advances in Pure Mathematics 2015年第5期5卷 251-266页

作者： Fei Xiong Liquan Mei Ying Li Wu Zhang Kunming Medical University Haiyuan College Kunming China School of Mathematics and Statistics Xi’an Jiaotong University Xi’an China School of Computer Engineering and Science Shanghai University Shanghai China

This paper describes a characteristics-mix finite element method for the computation of incompressible Navi-er-Stokes equations with variable density. We have introduced a mixed scheme which combines a characteristics finite element scheme for treating the mass conservation equation and a finite element method to deal with the momentum equation and the divergence free constraint. The proposed method has a lot of attractive computational properties: parameter-free, very flexible, and averting the difficulties caused by the original equations. The stability of the method is proved. Finally, several numerical experiments are given to show that this method is efficient for variable density incompressible flows problem.

关键词： Characteristic Finite Element Variable Density flows Naiver-Stokes Equations Stabilized Method