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Showing papers in "Annual Review of Fluid Mechanics in 1996"


Journal ArticleDOI
TL;DR: A review of wake vortex dynamics can be found in this article, with a focus on the three-dimensional aspects of nominally two-dimensional wake flows, as well as the discovery of several new phenomena in wakes.
Abstract: Since the review of periodic flow phenomena by Berger & Wille (1972) in this journal, over twenty years ago, there has been a surge of activity regarding bluff body wakes. Many of the questions regarding wake vortex dynamics from the earlier review have now been answered in the literature, and perhaps an essential key to our new understandings (and indeed to new questions) has been the recent focus, over the past eight years, on the three-dimensional aspects of nominally two-dimensional wake flows. New techniques in experiment, using laser-induced fluorescence and PIV (Particle-Image-Velocimetry), are vigorously being applied to wakes, but interestingly, several of the new discoveries have come from careful use of classical methods. There is no question that strides forward in understanding of the wake problem are being made possible by ongoing three- dimensional direct numerical simulations, as well as by the surprisingly successful use of analytical modeling in these flows, and by secondary stability analyses. These new developments, and the discoveries of several new phenomena in wakes, are presented in this review.

3,206 citations


Journal ArticleDOI
TL;DR: In this article, a large-eddy simulation (LES) formalism, along with various subgrid-scale models developed since Smagorinsky's model, is presented, with an emphasis on the generation of coherent vortices.
Abstract: The paper presents large-eddy simulation (LES) formalism, along with the various subgrid-scale models developed since Smagorinsky’s model. We show how Kraichnan’s spectral eddy viscosity may be implemented in physical space, yielding the structure-function model. Recent developments of this model that allow the eddy viscosity to be inhibited in transitional regions are discussed. We present a dynamic procedure, where a double filtering allows one to dynamically determine the subgrid-scale model constants. The importance of backscatter effects is discussed. Alternatives to the eddy-viscosity assumption, such as scale- similarity models, are considered. Pseudo-direct simulations in which numerical diffusion replaces subgrid transfers are mentioned. Various applications of LES to incompressible and compressible turbulent flows are given, with an emphasis on the generation of coherent vortices

1,101 citations


Journal ArticleDOI
TL;DR: In this article, a review of numerical models for turbulent fluid-particle flows is presented, which is structured according to the turbulence models used for the continuous phase: turbulence energy-dissipation models, large eddy simulations, direct numerical simulations, and discrete vortex models.
Abstract: Numerical models for turbulent fluid-particle flows are reviewed. The two approaches typically used for modelling the dispersed (particle) phase are the trajectory and two-fluid formulations, while volume- averaged models are most common for the continuous (fluid) phase. The review is structured according to the turbulence models used for the continuous phase: turbulence energy-dissipation models, large- eddy simulations, direct numerical simulations, and discrete vortex models. The applications of these models to simulate particle dispersion due to fluid turbulence and the adjustments to the models to account for the modulation of the carrier phase turbulence by the particles are addressed.

592 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a model to predict the occurrence and dynamics of breaking, which is a major impediment to the development of better wind-wave and mixed-layer models, and showed that modern acoustic and electromagnetic oceanographic instrumentation should lead to significantly improved measurements of breaking in the near future.
Abstract: Breaking serves to limit the height of surface waves, mix the surface waters, generate ocean currents, and enhance air-sea fluxes of heat, mass, and momentum through the generation of turbulence and the entrainment of air. Breaking may result from intrinsic instabilities of deep-water waves or through wavewave, wave-current, and wind-wave interactions. Observations in the field are made difficult by the fact that breaking is a strongly nonlinear intermittent process occurring over a wide range of scales. Controlled laboratory studies of breaking have proven useful in measuring the scaling relationships between the surface wave field and the kinematics and dynamics of breaking. Our inability to predict the occurrence and dynamics of breaking is a major impediment to the development of better wind-wave and mixed-layer models. Modern acoustic and electromagnetic oceanographic instrumentation should lead to significantly improved measurements of breaking in the near future.

494 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examine the growing body of knowledge surrounding how the presence of elasticity in homogeneous, flowing polymeric fluids can act in isolation to create flow bifurcation and change.
Abstract: Purely elastic flow instabilities-those occurring in the absence of inertial forces-in flows used for the measurement of fluid viscometric parameters are reviewed. In particular, we examine the growing body of knowledge surrounding how the presence of elasticity in homogeneous, flowing polymeric fluids can act in isolation to create flow bifurcation and change. The field of inquiry is relatively new, and the studies that have played a key role in developing the science include a balance of experiment, large-scale computer simulation, and analytic stability theory. All are reviewed with a focus on how each has contributed to the understanding of novel physical mechanisms and principles governing these instabilities. The flows examined are simple, but critically important to the measurement devices common to tne laboratories of rheologists and fluids engineers. Moreover, it is clear that the knowledge gained from these studies may be generally applicable to a wide range of much more complicated flows that demonstrate this type of instability.

438 citations


Journal ArticleDOI
TL;DR: In this article, the authors provide a critical evaluation of linear stability theory for wall-bounded shear flows, with an emphasis on results, not techniques, and deal with applications to different flowfields related to aircraft systems.
Abstract: The objective of this review is to provide a critical evaluation of linear stability theory for wall-bounded shear flows, with an emphasis on results, not techniques. The results deal with applications to different flowfields related to aircraft systems. Because the flight condition is usually a low-disturbance environment, stability plays an important role in the transition process. Linear stability theory is not a new topic, so emphasis is placed on the most recent accomplishments.

401 citations


Journal ArticleDOI
TL;DR: A review of advances in understanding and predicting the behavior of scramjet combustion systems since the classic article published in this series by Antonio Fed (1973) can be found in this article.
Abstract: This paper reviews important advances in understanding and predicting the behavior of scramjet combustion systems since the classic article published in this series by Antonio Fed (1973). The review focuses on basic fluid phenomena and is divided into three distinct sections. The first briefly describes progress that has been made in the design and demonstration of practical scramjets around the world, especially in the US, the FSU, France, and Germany. The second provides a contemporary exposition of the aerothermodynamics of the dual-mode ramjetkcramjet combustion system, accounting for the role of the isolator in preventing unstart from either thermal choking or flow separation due to heat release. The third part summarizes the current state of knowledge regarding fuel- air mixing in dual-mode ramjetkcramjet combustors, especially the potential of axial vorticity to increase mixing effectiveness over that of lateral vorticity.

258 citations


Journal ArticleDOI
TL;DR: In this article, the authors reviewed the recent advances in computations of incompressible flows involving a fully nonlinear free surface and (large) nonlinearity, and concluded that computations for nonlinear potential-flow wave problems are reasonably mature, although further developments are needed for large complex problems.
Abstract: Recent advances in computations of incompressible flows involving a fully nonlinear free surface are reviewed. Focus is on the treatment of the free surface and (large) nonlinearity. Both potential as well as rotational and viscous free-surface flows are considered. For the former, Mixed-Eulerian-Langrangian boundary-integral methods and the recently developed high-order spectral methods are reviewed. For the latter, the focus is mainly on volume-discretization methods utilizing Eulerian or boundary-fitted grids. The importance and proper treatment of viscous free-surface conditions for these problems are emphasized. It is concluded that computations for nonlinear potential-flow wave problems are reasonably mature although further developments to improve efficiency and robustness are needed for large complex problems.

255 citations


Journal ArticleDOI
TL;DR: In this article, a hierarchy of prototype flows, paying special attention to phenomena that cannot be described completely by the equations of motion, such as flow-induced breakup and coalescence of fluid phases.
Abstract: Understanding the motion of immiscible fluids in porous media is a challenging problem in low-Reynolds-number hydrodynamics that is relevant to many processes of technological and biological interest. Simple representations of the flow on the scale of individual pores or channels have proven useful in exposing effects of various parameters on fluid motion and in identifying flow-induced changes in the spatial configurations of the fluids, which can affect the mobilities of the phases. This paper examines a hierarchy of such prototype flows, paying special attention to phenomena that cannot be described completely by the equations of motion, such as flow-induced breakup and coalescence of fluid phases. In these cases, connections between numerical computations and experiments are especially significant, which is apparent in the studies reviewed here.

188 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe a number of analyses and experi- ments that could eventually serve to elucidate the physics of fluid mechanics phe- nomena such as the generation of whirls, the quasi-two-dimensionalization of tur- bulence near the free surface, and the reverse energy cascade at pure and contam- inated interfaces.
Abstract: The central intent of this paper is to describe a number of analyses and experi- ments that could eventually serve to elucidate the physics of fluid mechanics phe- nomena such as the generation of whirls, the quasi-two-dimensionalization of tur- bulence near the free surface, and the reverse energy cascade at pure and contam- inated interfaces. Discussed in some detail are the vorticity flux; surface-tension effects; basic equations and boundary conditions; the role of surfactants; topol- ogy of interfacial interactions; characteristics of connections, disconnections, and reconnections; a number of canonical flows (single and paired vortices, jets, and vortex rings); and the need for the development of prediction methods for turbulent flows in a region bounded by a free-surface, solid-fluid juncture boundary layer and the nonlinear interactions of shear flow wake turbulence with a free surface.

146 citations


Journal ArticleDOI
TL;DR: In this article, a review of two-dimensional solutions, both Boussinesq and non-Boussineq, linear and nonlinear, is presented, along with relevant numerical simulation graphics.
Abstract: The atmospheric lee wave is a disturbance propagated by buoyancy and arising from an isolated source, usually by flow over ridges and mountains. Part of this review treats two-dimensional solutions, both Boussinesq and non-Boussinesq, linear and nonlinear. These discussions emphasize trapped waves, the downslope windstorm, the drag on the earth and the upward momentum flux, the hydro- static approximation and its limitations, effects of critical layers, and middle atmospheric wave breaking. Three-dimensional Boussinesq linear and nonlinear solutions are also discussed; shown are the variety of regimes possible, from ship waves to shedding vortices. Photographs of natural phenomena are pre- sented as realizations, together with relevant numerical simulation graphics. The difficulties and achievements of simulation models are also outlined.

Journal ArticleDOI
TL;DR: In this paper, the authors review the history, formulation, and solution behavior of relatively comprehensive numerical models for the oceanic general circulation under equilibrium surface wind stress and buoyancy flux forcing and discuss the issues of model formulation are both the customary and alternative dynamical approximations of the fundamental fluid dynamics, parameterization of essential processes that occur on spatial and temporal scales smaller than can be resolved in model calculations, the boundary and initial conditions, the domain geometry, and the numerical algorithms.
Abstract: This article reviews the history, formulation, and solution behavior of relatively comprehensive numerical models for the oceanic general circulation under equilibrium surface wind stress and buoyancy flux forcing. The issues of model formulation are both the customary and alternative dynamical approximations of the fundamental fluid dynamics, the parameterization of essential processes that occur on spatial and temporal scales smaller than can be resolved in model calculations, the boundary and initial conditions, the domain geometry, and the numerical algorithms. The solution features discussed here are the wind- and buoyancy-driven lateral gyres in enclosed basins, the mostly longitudinal currents near the equator and around Antarctica, the overturning circulations, the chemical property distributions, and both forced and spontaneous variabitions about the time-mean circulation, occurring with both meso- and large-scale flow structures.

Journal ArticleDOI
TL;DR: In this article, the authors summarized recent progress made in physically understanding and numerically describing the coupled fluid and structural dynamics of parachute inflation, including porous, bluff-body aero- dynamics, highly deformable structures that change shape rapidly in response to the surrounding flow field, and time-dependent flow phenomena caused by the rapid deceleration of the parachute and payload.
Abstract: The inflation of a modern parachute encompasses several of the most com- plex phenomena in classical fluid dynamics, such as porous, bluff-body aero- dynamics; highly deformable structures that change shape rapidly in response to the surrounding flow field; and time-dependent flow phenomena caused by the rapid deceleration of the parachute and payload. This article summarizes recent progress made in physically understanding and numerically describing the coupled fluid and structural dynamics of parachute inflation. Experimental and computational advances in the modeling of bluff-body flows and parachute infla- tion are reviewed. The development of computational parachute inflation models has progressed to the point where their potential value has been proved, but they are not yet ready to be used as trusted parachute design tools. The ultimate goal is to predict with confidence the fully coupled time-dependent fluid dynamics and structural dynamics of parachutes in flight before flying them.