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Showing papers in "Annual Review of Fluid Mechanics in 2001"


Journal ArticleDOI
TL;DR: In this paper, the authors review the fluid mechanics and rheology of dense suspensions, emphasizing investigations of microstructure and total stress, and explore scaling theories and the development of constitutive equations.
Abstract: ▪ Abstract We review the fluid mechanics and rheology of dense suspensions, emphasizing investigations of microstructure and total stress. “Dense” or “highly concentrated” suspensions are those in which the average particle separation distance is less than the particle radius. For these suspensions, multiple-body interactions as well as two-body lubrication play a significant role and the rheology is non-Newtonian. We include investigations of multimodal suspensions, but not those of suspensions with dominant nonhydrodynamic interactions. We consider results from both physical experiments and computer simulations and explore scaling theories and the development of constitutive equations.

806 citations


Journal ArticleDOI
TL;DR: In this article, the authors present a review of the physical models for a fluid undergoing time-dependent motes and their applications in many fields of engineering, such as aeronautic and structural engineering.
Abstract: ▪ Abstract The interaction of a flexible structure with a flowing fluid in which it is submersed or by which it is surrounded gives rise to a rich variety of physical phenomena with applications in many fields of engineering, for example, the stability and response of aircraft wings, the flow of blood through arteries, the response of bridges and tall buildings to winds, the vibration of turbine and compressor blades, and the oscillation of heat exchangers. To understand these phenomena we need to model both the structure and the fluid. However, in keeping with the overall theme of this volume, the emphasis here is on the fluid models. Also, the applications are largely drawn from aerospace engineering although the methods and fundamental physical phenomena have much wider applications. In the present article, we emphasize recent developments and future challenges. To provide a context for these, the article begins with a description of the various physical models for a fluid undergoing time-dependent mot...

556 citations


Journal ArticleDOI
TL;DR: In this article, the authors review recent advances in understanding the fundamental mechanics of flexible-tube flows and discuss physiological applications spanning the cardiovascular system, respiratory system, and elsewhere in the body (involving active peristaltic transport driven by fluid structure/muscle interactions).
Abstract: ▪ AbstractAlmost all vessels carrying fluids within the body are flexible, and interactions between an internal flow and wall deformation often underlie a vessel's biological function or dysfunction. Such interactions can involve a rich range of fluid-mechanical phenomena, including nonlinear pressure-drop/flow-rate relations, self-excited oscillations of single-phase flow at high Reynolds number and capillary-elastic instabilities of two-phase flow at low Reynolds number. We review recent advances in understanding the fundamental mechanics of flexible-tube flows, and discuss physiological applications spanning the cardiovascular system (involving wave propagation and flow-induced instabilities of blood vessels), the respiratory system (involving phonation, the closure and reopening of liquid-lined airways, and Marangoni flows on flexible surfaces), and elsewhere in the body (involving active peristaltic transport driven by fluid-structure/muscle interactions).

423 citations


Journal ArticleDOI
TL;DR: In this paper, the authors review recent applications of computational fluid dynamics to simulate the motion in particle suspensions with both inertia and vorticity in the continueous phase, and discuss two special cases of inertial suspensions, for which detailed kinetic theories have been developed.
Abstract: ▪ Abstract The current understanding of the average flow properties of packed beds and particle suspensions, in which inertia plays a significant role on the particle length scale, is examined. The features of inertial suspensions posing challenges to theoriticians include the nonlinear and unsteady nature of the governing equations, the inability to superimpose solutions, the prevalence of hydrodynamic instabilities, and the existence of particle-particle collisions. We discuss two special cases of inertial suspensions, for which detailed kinetic theories have been developed: (a) particles in a gas, and (b) spherical, high-Reynolds number bubbles in liquid. Subsequently, we review recent applications of computational fluid dynamics to simulate the motion in particle suspensions with both inertia and vorticity in the continueous phase. The synthesis of these analytical and numerical techniques is a promising approach to address the many challenges of modelling inertial suspensions.

351 citations


Journal ArticleDOI
TL;DR: In this paper, the importance of the two-particle acceleration covariance in relative dispersion is demonstrated from the kinematics of the motion of particle-pairs, with emphasis on the assumptions and constraints involved, and on predictions of the scalar variance field for inhomogeneous sources.
Abstract: ▪ Abstract This review begins with the classical foundations of relative dispersion in Kolmogorov's similarity scaling. Analysis of the special cases of isotropic and homogeneous scalar fields is then used to establish most simply the connection with turbulent mixing. The importance of the two-particle acceleration covariance in relative dispersion is demonstrated from the kinematics of the motion of particle-pairs. A summary of the development of two-particle Lagrangian stochastic models is given, with emphasis on the assumptions and constraints involved, and on predictions of the scalar variance field for inhomogeneous sources. Two-point closures and kinematic simulation are also reviewed in the context of their prediction of the Richardson constant and other fundamental constants. In the absence of reliable field data, direct numerical simulations and laboratory measurements seem most likely to provide suitable data with which to test the assumptions and predictions of these theories.

302 citations


Journal ArticleDOI
Ilan Kroo1
TL;DR: Focusing on relatively high-aspect-ratio subsonic wings, the review suggests that opportunities for new concepts remain, but the greatest challenge lies in their integration with other aspects of the system.
Abstract: ▪ Abstract This article describes some of the fundamental ideas underlying methods for induced-drag prediction and reduction. A review of current analysis and design methods, including their development and common approximations, is followed by a survey of several approaches to lift-dependent drag reduction. Recent concepts for wing planform optimization, highly nonplanar surfaces, and various tip devices may lead to incremental but important gains in aircraft performance. Focusing on relatively high-aspect-ratio subsonic wings, the review suggests that opportunities for new concepts remain, but the greatest challenge lies in their integration with other aspects of the system.

231 citations


Journal ArticleDOI
TL;DR: In this article, the Critical Point Theory (CPT) was introduced to provide a rational definition of separation in three-dimensional flows and demonstrated by Henri Werle in the Onera water tunnel laboratory.
Abstract: ▪ Abstract The description and the physical understanding of three-dimensional separated flows are challenging problems mainly because of the use of inappropriate terms linked to the consideration of two-dimensional flows. This fact was realized in the early 1950s by Robert Legendre, who introduced the basic concepts of the Critical Point Theory to provide a rational definition of separation in three-dimensional flows. In parallel, demonstrative experiments were executed by Henri Werle in the Onera water tunnel laboratory. From the close cooperation between these two scientists resulted the construction of a powerful theoretical tool allowing the elucidation of the structure of largely separated three-dimensional fields. The importance of their contribution to fluid mechanics is illustrated here by the consideration of basic configurations: flow past wings or elongated bodies, in front of obstacles, and behind a base. For each case, the flow organization is discussed by considering representative water tu...

215 citations


Journal ArticleDOI
TL;DR: In this paper, the authors highlight the differences between the aerodynamics of high-speed trains and other types of transportation vehicles, including other vehicles, such as cars, buses, and trucks.
Abstract: This review highlights the differences between the aerodynamics of high-speed trains and other types of transportation vehicles. The emphasis is on modern, high-speed trains, including magnetic levitation (Maglev) trains. Some of the key differences are derived from the fact that trains operate near the ground or a track, have much greater length-to-diameter ratios than other vehicles, pass close to each other and to trackside structures, are more subject to crosswinds, and operate in tunnels with entry and exit events. The coverage includes experimental techniques and results and analytical and numerical methods, concentrating on the most recent information available.

215 citations


Journal ArticleDOI
TL;DR: Fluid mechanics research related to fire is reviewed with focus on canonical flows, multiphysics coupling aspects, experimental and numerical techniques in this paper, where buoyancy plans an important role.
Abstract: Fluid mechanics research related to fire is reviewed with focus on canonical flows, multiphysics coupling aspects, experimental and numerical techniques. Fire is a low-speed, chemically-reacting, flow in which buoyancy plans an important role. Fire research has focused on two canonical flows, the reacting boundary-layer and the reacting free plume. There is rich, multi-lateral, bi-directional, coupling among fluid mechanics and scalar transport, combustion, and radiation. There is only a limited experimental fluid-mechanics database for fire due to measurement difficulties in the harsh environment, and the focus within the fire community on thermal/chemical consequences. Increasingly, computational fluid dynamics techniques are being used to provide engineering guidance on thermal/chemical consequences and to study fire phenomenology.

96 citations


Journal ArticleDOI
TL;DR: In this paper, a review examines recent modeling and numerical simulation studies as well as the mechanisms that control flow and turbulence around shelterbelts and windbreaks and compare numerical simulations with experimental data and explain the relationships between sheltering effects and the structure of windbreaks.
Abstract: Shelterbelts or windbreaks were used for centuries to reduce wind speed, to control heat and moisture transfer and pollutant diffusion, to improve climate and environment, and to increase crop yields; but only within the last few decades have systematic studies considered the aerodynamics and shelter mechanisms of shelterbelts and windbreaks. This review examines recent modeling and numerical simulation studies as well as the mechanisms that control flow and turbulence around shelterbelts and windbreaks. We compare numerical simulations with experimental data and explain the relationships between sheltering effects and the structure of shelterbelts and windbreaks. We discuss how and why the desired effects are achieved by using numerical analysis. This chapter begins with the derivation of a general equation set for porous shelterbelts and windbreaks; the numerical model and simulation procedure are developed; unseparated and separated flows are predicted and characterized; the momentum budget and shelter mechanisms are analyzed; the effects of wind direction, density, width, and three dimensionality of shelterbelt structure on flow and turbulence are systematically described. Recent modeling and simulation of heat flux and evapotranspiration are also summarized. Finally, we discuss the use of high-performance distributed and parallel computing as well as clusters of networked workstations to enhance performance of the model applied to simulations of shelterbelts and windbreaks.

93 citations


Journal ArticleDOI
TL;DR: In this article, the authors consider the effect of spin-over and spin-down on the rotation of a viscous container and compare experimental and non-linear results with theory and experiment.
Abstract: We consider the manner in which a container filled with viscous fluid adjusts to changes in its rotation rate. We begin with homogeneous flows involving small departures in rotation rate from an initial state of solid-body rotation in an axisymmetric container. This is followed by a summary of other more recent developments, including weakly and fully nonlinear calculations and comparison with experiment and the question of spin-down. The question of "spin-over" is addressed, followed by a brief synopsis of free-surface effects, and a discussion of nonaxisymmetric spin-up. The second part of the review focuses on the effects of stratification on the spin-up process. Linearized (low Rossby number) spin-up within a cylindrical container is described. Thereafter, both experimental and nonlinear computational results are described and compared. The final section focuses on stratified spin-up and spin-down in conical geometries, and a number of comparisons between theory and experiment are given.


Journal ArticleDOI
TL;DR: The early work of Ricardo is described in this article, in which squish is used in flat-head engines to generate turbulence levels comparable to those in overhead-valve engines, leading to rapid flame propagation and suppressing knock.
Abstract: ▪ Abstract Early work of Ricardo is described, in which squish is used in flat-head engines to generate turbulence levels comparable to those in overhead-valve engines, leading to rapid flame propagation, and suppressing knock. Work by NACA before World War II is described, in which turbulence levels were measured in overhead-valve engines, indicating indirectly that surprisingly high levels were achieved just before ignition, possibly due to a tumble instability. Finally, work of Obukhov of 30 years ago is described, in which instabilities of tumbling flow are investigated in ellipsoids crudely modeling the engine cylinder as the piston rises; this suggests that there is an instability leading to intense small-scale motion just before ignition. Suggestions for further work are given.

Book ChapterDOI
TL;DR: In this paper, an interactive boundary-layer theory is introduced in the context of unsteady separation, leading onto a consideration of large-Reynolds number asymptotic instability theory.
Abstract: Boundary-layer theory is crucial in understanding why certain phenomena occur. We start by reviewing steady and unsteady separation from the viewpoint of classical non-interactive boundary-layer theory. Next, interactive boundary-layer theory is introduced in the context of unsteady separation. This discussion leads onto a consideration of large-Reynolds-number asymptotic instability theory. We emphasize that a key aspect of boundary-layer theory is the development of singularities in solutions of the governing equations. This feature, when combined with the pervasiveness of instabilities, often forces smaller and smaller scales to be considered. Such a cascade of scales can limit the quantitative usefulness of solutions. We also note that classical boundary-layer theory may not always be the large-Reynolds-number limit of the Navier-Stokes equations, because of the possible amplification of short-scale modes, which are initially exponentially small, by a Rayleigh instability mechanism.