Showing papers on "Fluid dynamics published in 2004"

Engineering flows in small devices

Abstract: Microfluidic devices for manipulating fluids are widespread and finding uses in many scientific and industrial contexts. Their design often requires unusual geometries and the interplay of multiple physical effects such as pressure gradients, electrokinetics, and capillarity. These circumstances lead to interesting variants of well-studied fluid dynamical problems and some new fluid responses. We provide an overview of flows in microdevices with focus on electrokinetics, mixing and dispersion, and multiphase flows. We highlight topics important for the description of the fluid dynamics: driving forces, geometry, and the chemical characteristics of surfaces.

Unit Operations of Chemical Engineering

Abstract: Part 1 Introduction: definitions and principles. Part 2 Fluid mechanics: fluid statics and its applications fluid flow phenomena basic equations of fluid flow flow of incompressible fluids in conduits and thin layers flow of compressible fluids flow past immersed bodies transportation and metering of fluids agitation and mixing of liquids. Part 3 Heat transfer and its applications: heat transfer by conduction principles of heat flow in fluids heat transfer to fluids without phase change heat transfer to fluids with heat change radiation heat transfer heat-exchange equipment evaporation. Part 4 Mass transfer and its applications: equilibrium stage operations distillation introduction to multicomponent distillation leaching and extraction principles of diffusion and mass transfer between phases gas absorption humidification operations drying of solids adsorption membrane separation processes crystallization. Part 5 Operations involving particulate solids properties, handling and mixing of particulate solids size reduction mechanical separations.

Fluid Mechanics: Fundamentals and Applications

Abstract: 1 Introduction and Basic Concepts2 Properties of Fluids3 Pressure and Fluid Statics4 Fluid Kinematics5 Bernoulli and Energy Equations6 Momentum and Analysis of Flow Systems7 Dimensional Analysis and Flow Systems8 Flow in Pipes9 Differential Analysis of Fluid Flow10 Approximations of the Navier-Stokes Equation11 Flow Over Bodies: Drag and Lift12 Compressible Flow13 Open-Channel Flow14 Turbomachinery15 Computational Fluid Dynamics (CFD)Appendices1 Property Tables and Charts (SI Units)2 Property Tables and Charts (English Units)3 Introduction to EES

Arbitrary Lagrangian–Eulerian Methods

Abstract: The aim of the present chapter is to provide an in-depth survey of arbitrary Lagrangian–Eulerian (ALE) methods, including both conceptual aspects of the mixed kinematical description and numerical implementation details. Applications are discussed in fluid dynamics, nonlinear solid mechanics and coupled problems describing fluid–structure interaction. The need for an adequate mesh-update strategy is underlined, and various automatic mesh-displacement prescription algorithms are reviewed. This includes mesh-regularization methods essentially based on geometrical concepts, as well as mesh-adaptation techniques aimed at optimizing the computational mesh according to some error indicator. Emphasis is then placed on particular issues related to the modeling of compressible and incompressible flow and nonlinear solid mechanics problems. This includes the treatment of convective terms in the conservation equations for mass, momentum, and energy, as well as a discussion of stress-update procedures for materials with history-dependent constitutive behavior. Keywords: ALE description; convective transport; finite elements; stabilization techniques; mesh regularization and adaptation; fluid dynamics; nonlinear solid mechanics; stress-update procedures; fluid–structure interaction

Experimental Observation of Nonlinear Traveling Waves in Turbulent Pipe Flow

Abstract: Transition to turbulence in pipe flow is one of the most fundamental and longest-standing problems in fluid dynamics. Stability theory suggests that the flow remains laminar for all flow rates, but in practice pipe flow becomes turbulent even at moderate speeds. This transition drastically affects the transport efficiency of mass, momentum, and heat. On the basis of the recent discovery of unstable traveling waves in computational studies of the Navier-Stokes equations and ideas from dynamical systems theory, a model for the transition process has been suggested. We report experimental observation of these traveling waves in pipe flow, confirming the proposed transition scenario and suggesting that the dynamics associated with these unstable states may indeed capture the nature of fluid turbulence.

Exact coherent structures in pipe flow: travelling wave solutions

Abstract: Three-dimensional travelling wave solutions are found for pressure-driven fluid flow through a circular pipe. They consist of three well-defined flow features – streamwise rolls and streaks which dominate and streamwise-dependent wavy structures. The travelling waves can be classified by the and traceable down to a Reynolds number (based on the mean velocity) of 1251. The new solutions are found using a constructive continuation procedure based upon key physical mechanisms thought generic to wall-bounded shear flows. It is believed that the appearance of these new alternative solutions to the governing equations as the Reynolds number is increased is a necessary precursor to the turbulent transition observed in experiments.

Simulation of buoyancy driven bubbly flow: Established simplifications and open questions

Abstract: An assessment is given of the present state of modeling and simulation of buoyancy driven gas-liquid bubble flow based on the two-fluid approach. Main points of discussion comprise the admissible model simplifications in order to obtain a more easily solvable model together with the question of which physical effects are of prime importance and which reliable correlations can be recommended or are still missing. It is shown that, for most practical cases, the two-fluid model can be simplified to a formulation which allows for the application of efficient solution strategies for single-phase flow. From the different interaction forces between gas and liquid, pressure and drag force are most important, whereas no sound experimental basis is available for (lateral) lift forces. So far, lift forces have primarily been used empirically to adjust the gas distribution to the experimental observation. The main open question concerns the prope! r modeling of turbulence in gas-liquid bubble flow since it affects both the mixture viscosity and the bubble dispersion. © 2004 American Institute of Chemical Engineers AIChE J, 50: 24–45, 2004

Imbibition in disordered media

Abstract: The physics of liquids in porous media gives rise to many interesting phenomena, including imbibition where a viscous fluid displaces a less viscous one. Here we discuss the theoretical and experimental progress made in recent years in this field. The emphasis is on an interfacial description, akin to the focus of a statistical physics approach. Coarse-grained equations of motion have been recently presented in the literature. These contain terms that take into account the pertinent features of imbibition: non-locality and the quenched noise that arises from the random environment, fluctuations of the fluid flow and capillary forces. The theoretical progress has highlighted the presence of intrinsic length-scales that invalidate scale invariance often assumed to be present in kinetic roughening processes such as that of a two-phase boundary in liquid penetration. Another important fact is that the macroscopic fluid flow, the kinetic roughening properties, and the effective noise in the problem are all coupled. Many possible deviations from simple scaling behaviour exist, and we outline the experimental evidence. Finally, prospects for further work, both theoretical and experimental, are discussed.

Causal theories of dissipative relativistic fluid dynamics for nuclear collisions

Abstract: Nonequilibrium fluid dynamics derived from the extended irreversible thermodynamics of the causal M\"uller-Israel-Stewart theory of dissipative processes in relativistic fluids based on Grad's moment method is applied to the study of the dynamics of hot matter produced in ultrarelativistic heavy ion collisions. The temperature, energy density, and entropy evolution are investigated in the framework of the Bjorken boost-invariant scaling limit. The results of these second order theories are compared to those of first order theories due to Eckart and to Landau and Lifshitz and those of zeroth order (perfect fluid) due to Euler. In the presence of dissipation perfect fluid dynamics is no longer valid in describing the evolution of the matter. First order theories fail in the early stages of evolution. Second order theories give a better description in good agreement with transport models. It is shown in which region the Navier-Stokes-Fourier laws (first order theories) are a reasonable limiting case of the more general extended thermodynamics (second order theories).

Elastic turbulence in curvilinear flows of polymer solutions.

Abstract: Following our first report (A Groisman and V Steinberg 2000 Nature 405 53), we present an extended account of experimental observations of elasticity-induced turbulence in three different systems: a swirling flow between two plates, a Couette–Taylor (CT) flow between two cylinders, and a flow in a curvilinear channel (Dean flow). All three set-ups had a high ratio of the width of the region available for flow to the radius of curvature of the streamlines. The experiments were carried out with dilute solutions of high-molecular-weight polyacrylamide in concentrated sugar syrups. High polymer relaxation time and solution viscosity ensured prevalence of non-linear elastic effects over inertial non-linearity, and development of purely elastic instabilities at low Reynolds number (Re) in all three flows. Above the elastic instability threshold, flows in all three systems exhibit features of developed turbulence. They include: (i) randomly fluctuating fluid motion excited in a broad range of spatial and temporal scales and (ii) significant increase in the rates of momentum and mass transfer (compared with those expected for a steady flow with a smooth velocity profile). Phenomenology, driving mechanisms and parameter dependence of the elastic turbulence are compared with those of the conventional high-Re hydrodynamic turbulence in Newtonian fluids. Some similarities as well as multiple principal differences were found. In two out of three systems (swirling flow between two plates and flow in the curvilinear channel), power spectra of velocity fluctuations decayed rather quickly, following power laws with exponents of about −3.5. It suggests that, being random in time, the flow is rather smooth in space, in the sense that the main contribution to deformation and mixing (and, possibly, elastic energy) is coming from flow at the largest scale of the system. This situation, random in time and smooth in space, is analogous to flows at small scales (below the Kolmogorov dissipation scale) in high-Re turbulence.

Dynamics of simple liquids at heterogeneous surfaces: molecular-dynamics simulations and hydrodynamic description.

Abstract: In this paper we consider the effect of surface heterogeneity on the slippage of fluid, using two complementary approaches. First, MD simulations of a corrugated hydrophobic surface have been performed. A dewetting transition, leading to a super-hydrophobic state, is observed for pressure below a “capillary” pressure. Conversely, a very large slippage of the fluid on this composite interface is found in this super-hydrophobic state. Second, we propose a macroscopic estimate of the effective slip length on the basis of continuum hydrodynamics, in order to rationalize the previous MD results. This calculation allows to estimate the effect of a heterogeneous slip length pattern at the composite interface. Comparison between the two approaches shows that they are in good agreement at low pressure, but highlights the role of the exact shape of the liquid-vapor interface at higher pressure. These results confirm that small variations in the roughness of a surface can lead to huge differences in the slip effect. On the basis of these results, we propose some guidelines to design highly slippery surfaces, motivated by potential applications in microfluidics.

Finite element developments for general fluid flows with structural interactions

Abstract: SUMMARY The objective in this paper is to present some developments for the analysis of Navier–Stokes incompressible and compressible fluid flows with structural interactions. The incompressible fluid is discretized with a new solution approach, a flow-condition-based interpolation finite element scheme. The high-speed compressible fluids are solved using standard finite volume methods. The fluids are fully coupled to general structures that can undergo highly non-linear response due to large deformations, inelasticity, contact and temperature. Particular focus is given on the scheme used to couple the fluid media with the structures. The fluids can also be modelled as low-speed compressible or slightly compressible media, which are important models in engineering practice. Some solutions obtained using ADINA are presented to indicate the analyses that can be performed. Copyright 2004 John Wiley & Sons, Ltd. The analysis of multiphysics problems, and specifically the solution of fluid–structure interactions, has been given increased attention during recent years [1]. This is largely because numerical methods have become very powerful and can be used at reasonable costs giving great benefits in scientific and engineering studies. Traditionally, fluid flows have been solved assuming rigid structures, and structures have been solved assuming fluid pressures. Sometimes iterations were used between the analyses of the two media to ensure that reasonable assumptions have been used in each case. However, there are many problems where a direct fully coupled analysis is needed to model the physics of the fluid–structure problem accurately. This is particularly the case when the structure undergoes large deformations in the interaction with the fluid and thermal effects need be included.

Size, shape and dynamics of large-scale turbulent flow structures in a gravel-bed river

Abstract: In this paper, we present a detailed investigation of the size, scale and dynamics of macro-turbulent flow structures in gravel-bed rivers. We used an array of seven electromagnetic current meters with high resolution in both space and time to measure the streamwise velocity fluctuations in a gravel-bed river. The array was deployed successively in various configurations in order to quantify the vertical, lateral and longitudinal extent of the flow structures and to estimate their advecting velocities. To depict the spatial and temporal properties of the flow structures, we used space–time velocity matrices, space–time correlation analysis and coherent-structure detection schemes. The results show that the large-scale turbulent flow structures in a gravel-bed river occupy the entire depth of the flow and that they are elongated and narrow. The length of the structures is 3 to 5 times the flow depth while the width is between 0.5 and 1 times flow depth. In spite of the high roughness of the bed, these values are similar to those reported in the literature for laboratory experiments on large-scale turbulent flow structures. The dynamics of the large-scale turbulent flow structures investigated using flow visualization highlight the interactions between the outer flow region and the near-bed region. Our evidence suggests that large-scale flow incursions trigger ejections in the near-bed region that can develop into megabursts that can reach the water surface.

Observation of Water Confined in Nanometer Channels of Closed Carbon Nanotubes

Abstract: We present a method to fill 2−5-nm-diameter channels of closed multiwalled carbon nanotubes (MWNT) with an aqueous fluid and perform in situ high-resolution observations of fluid dynamic behavior in this confined system. Transmission electron microscope (TEM) observations confirm the successful filling of two types of MWNTs and reveal disordered gas/liquid interfaces contrasting the smooth curved menisci visualized previously in MWNT with diameter above 10 nm. Electron energy loss spectroscopy (EELS) and energy dispersive spectrometry (EDS) analyses, along with TEM simulation, indicate the presence of water in MWNT. A wet−dry transition on the nanometer scale is also demonstrated by means of external heating. The results suggest that when ultrathin channels such as carbon nanotubes contain water, fluid mobility is greatly retarded compared to that on the macroscale. The present findings pose new challenges for modeling and device development work in this area.

CFD study of fluid flow and wall heat transfer in a fixed bed of spheres

Abstract: A study is presented of the relationship between the local flow field and the local wall heat flux in a packed bed of spheres. Computational fluid dynamics is used as a tool for obtaining the detailed velocity and temperature fields, for gas flowing through a periodic wall segment test cell. Results from the wall segment are demonstrated to reproduce those obtained from a full bed of spheres with tube-to-particle diameter ratio of N = 4. Attempts to correlate the local wall heat flux with local properties of the flow field, such as velocity components, velocity gradients, and components of vorticity, led to the conclusion that local heat transfer rates do not correlate statistically with the local flow field. Instead, a conceptual analysis was used to suggest that local patterns of wall heat flux are related to larger-scale flow structures in the bed. © 2004 American Institute of Chemical Engineers AIChE J, 50: 906–921, 2004

On two-phase sediment transport: sheet flow of massive particles

Abstract: A model is presented for concentrated sediment transport that is driven by strong, fully developed turbulent shear flows over a mobile bed. Balance equations for the average mass, momentum and energy for the two phases are phrased in terms of concentration–weighted (Favre averaged) velocities. Closures for the correlations between fluctuations in concentration and particle velocities are based on those for collisional grain flow. This is appropriate for particles that are so massive that their fall velocity exceeds the friction velocity of the turbulent fluid flow. Particular attention is given to the slow flow in the region of high concentration above the stationary bed. A failure criterion is introduced to determine the location of the stationary bed. The proposed model is solved numerically with a finite–difference algorithm in both steady and unsteady conditions. The predictions of sediment concentration and velocity are tested against experimental measurements that involve massive particles. The model is further employed to study several global features of sheet flow such as the total sediment transport rate in steady and unsteady conditions.

Numerical and analytical calculations of the temperature and flow field in the upwind power plant

Abstract: The upwind power plant is an interesting system to generate electrical power from free solar energy. The authors have carried out an analysis to improve the description of the operation mode and efficiency. The pressure drop at the turbine and the mass flow rate have a decisive influence on the efficiency. This can be determined only by coupling of all parts of an upwind power plant. In this study the parts ground, collector, chimney and turbine are modelled together numerically. The basis for all sections is the numerical CFD programme FLUENT. This programme solves the basic equations of the thermal fluid dynamics. Model development and parameter studies particularly arise with this tool. Additional to the calculations using FLUENT a simple model is developed for comparison purposes and parameter studies. The numerical results with FLUENT compare well with the results given by the simple model, therefore, we can use the simple model for parameter studies. The basis for the geometry is the prototype Manzanares. Copyright © 2004 John Wiley & Sons, Ltd.

Control‐volume method for numerical simulation of two‐phase immiscible flow in two‐ and three‐dimensional discrete‐fractured media

Abstract: [1] We provide a numerical procedure for the simulation of two-phase immiscible and incompressible flow in two- and three-dimensional discrete-fractured media. The concept of cross-flow equilibrium is used to reduce the fracture dimension from n to (n-1) in the calculation of flow in the fractures. This concept, which is often referred to as the discrete-fracture model, has a significant effect on the reduction of computational time. The spatial discretization is performed with the control-volume method. This method is locally conservative and allows the use of unstructured grids to represent complex geometries, such as discrete-fracture configurations. The relative permeability is upwinded with a criterion based on the evaluation of the flux direction at the boundaries of the control volumes, which is consistent with the physics of fluid flow. The system of partial differential equations is decoupled and solved using the implicit-pressure, explicit-saturation (IMPES) approach. The algorithm has been successfully tested in two- and three-dimensional numerical simulations of wetting phase fluid injection (such as water) in discrete-fractured media saturated by a nonwetting phase (such as nonaqueous phase liquid or oil) with mild to high nonlinearity in relative permeability and capillary pressure. To the best of our knowledge, results for simulations of two-phase immiscible and incompressible flow in three-dimensional discrete-fractured media, including capillary and gravity effects, are the first to appear in the literature.

Overview of the lattice Boltzmann method for nano- and microscale fluid dynamics in materials science and engineering

Abstract: The article gives an overview of the lattice Boltzmann method as a powerful technique for the simulation of single and multi-phase flows in complex geometries. Owing to its excellent numerical stability and constitutive versatility it can play an essential role as a simulation tool for understanding advanced materials and processes. Unlike conventional Navier–Stokes solvers, lattice Boltzmann methods consider flows to be composed of a collection of pseudo-particles that are represented by a velocity distribution function. These fluid portions reside and interact on the nodes of a grid. System dynamics and complexity emerge by the repeated application of local rules for the motion, collision and redistribution of these coarse-grained droplets. The lattice Boltzmann method, therefore, is an ideal approach for mesoscale and scale-bridging simulations. It is capable to tackling particularly those problems which are ubiquitous characteristics of flows in the world of materials science and engineering, namely, flows under complicated geometrical boundary conditions, multi-scale flow phenomena, phase transformation in flows, complex solid–liquid interfaces, surface reactions in fluids, liquid–solid flows of colloidal suspensions and turbulence. Since the basic structure of the method is that of a synchronous automaton it is also an ideal platform for realizing combinations with related simulation techniques such as cellular automata or Potts models for crystal growth in a fluid or gas environment. This overview consists of two parts. The first one reviews the philosophy and the formal concepts behind the lattice Boltzmann approach and presents also related pseudo-particle approaches. The second one gives concrete examples in the area of computational materials science and process engineering, such as the prediction of lubrication dynamics in metal forming, dendritic crystal growth under the influence of fluid convection, simulation of metal foam processing, flow percolation in confined geometries, liquid crystal hydrodynamics and processing of polymer blends.

Apparatus and method for providing fluid for immersion lithography

Abstract: Embodiments of the present invention are directed to a system and a method of controlling the fluid flow and pressure to provide stable conditions for immersion lithography. A fluid is provided in a space (34) between the lens (22) and the substrate (16) during the immersion lithography process. Fluid is supplied to the space and is recovered from the space through a porous member (51) in fluidic communication with the space. Maintaining the pressure in the porous member under the bubble point of the porous member can eliminate noise created by mixing air with the fluid during fluid recovery. In one embodiment, the method comprises drawing the fluid from the space via a recovery flow line through a porous member; and maintaining a pressure of the fluid in the porous member below a bubble point of the porous member during drawing of the fluid from the space.

High-Resolution Methods for Incompressible and Low-Speed Flows

Abstract: Fundamental Physical and Model Equations.- The Fluid Flow Equations.- The Viscous Fluid Flow Equations.- Curvilinear Coordinates and Transformed Equations.- Overview of Various Formulations and Model Equations.- Basic Principles in Numerical Analysis.- Time Integration Methods.- Numerical Linear Algebra.- Solution Approaches.- Compressible and Preconditioned-Compressible Solvers.- The Artificial Compressibility Method.- Projection Methods: The Basic Theory and the Exact Projection Method.- Approximate Projection Methods.- Modern High-Resolution Methods.- to Modern High-Resolution Methods.- High-Resolution Godunov-Type Methods for Projection Methods.- Centered High-Resolution Methods.- Riemann Solvers and TVD Methods in Strict Conservation Form.- Beyond Second-Order Methods.- Applications.- Variable Density Flows and Volume Tracking Methods.- High-Resolution Methods and Turbulent Flow Computation.