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- Volume 39, 2007
Annual Review of Fluid Mechanics - Volume 39, 2007
Volume 39, 2007
- Preface
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H. Julian Allen: An Appreciation*
Vol. 39 (2007), pp. 1–17More LessAbstractHarvey Allen is best known as the genius behind the blunt-body concept, published in 1953, which enables spacecraft to return safely home through Earth's dense atmosphere. He was also an extraordinary research leader, who led a world-class research program in hypersonics at the NACA Ames Aeronautical Laboratory. This paper reviews his career as one of America's leading theorists and experimenters, including his engineering education at Stanford, his work on the inverse problem of calculating the airfoil profile to obtain a desired pressure distribution, his hand in constructing wind tunnels and experimental facilities at Ames, and his pioneering and wide-ranging work on atmospheric re-entry. It concludes with an appreciation of his uniquely inspirational style of research management, and of his magnetic personality.
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Osborne Reynolds and the Publication of His Papers on Turbulent Flow
Vol. 39 (2007), pp. 19–35More LessAbstractFollowing The Royal Society's decision to allow the release of hitherto confidential documents concerning referees' reports and other material relating to the publication of historical manuscripts, the present paper examines the exchanges preceding the publication of the two papers on turbulent flow by Osborne Reynolds that have so greatly influenced the development of Engineering Fluid Mechanics over the past century. The documents cited reveal that, although the earlier experimental paper was warmly welcomed, the referees were critical of the subsequent analytical contribution. It appears that the publication of the latter paper was due mainly to the considerable standing Reynolds had by then acquired, in part from the impact of his experimental paper published 12 years earlier. The paper also provides a summary of Reynolds' career and research prior to his embarking on the research published in the two seminal papers.
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Hydrodynamics of Coral Reefs
Vol. 39 (2007), pp. 37–55More LessAbstractThe geometric complexity of coral reefs leads to interesting fluid mechanics problems at scales ranging from those of coral colonies or even branches a few millimeters in diameter up to whole reefs that can be kilometers in horizontal extent. In many cases, both at the colony and reef scale, unsteady flows, usually due to surface waves, behave very differently than do steady flows for which the coral structures may appear to have quite high resistance to any flow through their interior. Allowing for this difference, engineering formulae for mass transfer describe well the uptake of nutrients by corals, although a priori determination of hydrodynamic roughness of corals and coral reefs is not yet possible. Surface wave-driven flows are a common feature of many coral reefs and appear to follow predictions of theories based on radiation stress gradients. However, comparisons to observations have been relatively limited, and there is some question as to the role played by Stokes drift in these flows. Like other near-shore environments, internal waves and flows driven by horizontal buoyancy gradients can also be important.
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Internal Tide Generation in the Deep Ocean
Chris Garrett, and Eric KunzeVol. 39 (2007), pp. 57–87More LessAbstractInternal tides are internal gravity waves generated in stratified waters by the interaction of barotropic tidal currents with variable bottom topography. They play a role in dissipating tidal energy and lead to mixing in the deep ocean. Key dimensionless parameters governing their generation include the tidal excursion compared with the scale of the topography, the bottom slope compared with the angle at which rays of internal waves of tidal frequency propagate, and the height of the topography compared with the depth of the ocean. Recent theoretical developments for parts of this parameter space particularly relevant to the deep ocean show that most of the energy flux is associated with low modes that propagate away from the generation region. For isolated features this energy flux is not strongly dependent on the bottom slope. Intense beams of internal tidal energy are expected near “critical slopes," bottom slopes equal to the ray slope, and lead to local mixing.
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Micro- and Nanoparticles via Capillary Flows
Vol. 39 (2007), pp. 89–106More LessAbstractThis review surveys some capillary flows capable of stretching fluid interfaces down to the micrometric dimension and below. These types of flows have become the basis for attractive techniques to produce monodisperse micro- and nanoparticles with either simple or core-shell structure (micro- and nanocapsules, coaxial nanofibers, and hollow nanofibers). These techniques enable precise control on the particle mean size. We also review the basic physics of the flow and the dimensionless parameters that govern these capillary flows. Some examples of the types of particles produced by a few devices are also presented.
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Transition Beneath Vortical Disturbances
Paul Durbin, and Xiaohua WuVol. 39 (2007), pp. 107–128More LessAbstractTheory and computer simulations have led to advances in the fundamental understanding of how vortical disturbances induce transition in an underlying boundary layer. It is an intriguing process whereby the shear filters the disturbance, admitting only long streamwise wavelengths into the boundary layer. These develop into strong jets in the perturbation velocity field, which lift up into the upper portion of the layer. Then shorter wavelength perturbations trigger breakdown, ultimately producing a turbulent patch near the wall. Pertinent linear theory has evolved with time, but only with recent computer simulations has it been fitted into a picture of transition beneath vortical disturbances.
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Nonmodal Stability Theory
Vol. 39 (2007), pp. 129–162More LessAbstractHydrodynamic stability theory has recently seen a great deal of development. After being dominated by modal (eigenvalue) analysis for many decades, a different perspective has emerged that allows the quantitative description of short-term disturbance behavior. A general formulation based on the linear initial-value problem, thus circumventing the normal-mode approach, yields an efficient framework for stability calculations that is easily extendable to incorporate time-dependent flows, spatially varying configurations, stochastic influences, nonlinear effects, and flows in complex geometries.
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Intrinsic Flame Instabilities in Premixed and Nonpremixed Combustion
Vol. 39 (2007), pp. 163–191More LessAbstractThe focus of this article is on intrinsic combustion instabilities in both premixed and nonpremixed systems, identifying, in particular, the roles of differential and preferential diffusion, thermal expansion, and heat losses. For premixed flames, the hydrodynamic instability resulting from thermal expansion plays a central role and is particularly dominant in large-scale flames. It is responsible for the formation of sharp folds and creases in the flame front and for the wrinkling observed over the surface of expanding flames. In contrast, instabilities in diffusion flames, which give rise to cellular and oscillating flames, are mainly driven by diffusive-thermal effects, with thermal expansion playing a secondary role. The discussion also includes instabilities of edge-flames in unmixed reactants, which possess stability characteristics of both premixed and diffusion flames, but with a distinct mode of instability.
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Thermofluid Modeling of Fuel Cells
Vol. 39 (2007), pp. 193–215More LessAbstractFuel cells offer the prospect of silent electrical power generation at high efficiency with near-zero pollutant emission. Many materials and fabrication problems have now been solved and attention has shifted toward system modeling, including the fluid flows that supply the cells with hydrogen and oxygen. This review describes the current thermofluid modeling capabilities for proton exchange membrane fuel cells (PEMFCs) and solid oxide fuel cells (SOFCs), the most promising candidates for commercial exploitation. Topics covered include basic operating principles and stack design, convective-diffusive flow in porous solids, special modeling issues for PEMFCs and SOFCs, and the use of computational fluid dynamics (CFD) methods.
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The Fluid Dynamics of Taylor Cones
Vol. 39 (2007), pp. 217–243More LessAbstractThe formation of cone-jets in charged liquids with electrical conductivities larger than 10−4 S/m is reviewed for steady supported menisci and transient Coulomb fissions in charged drops. Taylor's hydrostatic model does not apply strictly, but it forms the basis for subsequent developments. The jet structure is critically dependent on the model used for charge transport, which has been based mostly on a constant conductivity assumption. Saville's (1997) more general model predicts the formation of rarefaction fronts with wide space charge–dominated regions near the liquid surface, which apparently do arise in polar liquids near the minimum flow rate. Known approximate scaling laws for the jet break down at electrical conductivities of about 1 S/m due to ion evaporation from the meniscus. In molten salts and liquid metals a regime of purely ionic emissions exists without drop or jet formation.
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Gravity Current Interaction with Interfaces
Vol. 39 (2007), pp. 245–261More LessAbstractGravity currents that impact interfaces have a number of features that differ from gravity currents in homogeneous or continuously stratified ambient fluid. The interface can cause sharp changes in the flow and split the current into an undercurrent in the dense layer and a filling intrusion in the upper layer. If the current penetrates the lower layer it can initiate large amplitude waves with a length scale several times larger than the scale of the head of the current. If the current carries particulate matter the change in flow at the interface changes the deposition of particles. Because approximate two-layer systems exist in nature, especially in basins ranging up to the size of the Arctic, and may affect global climate, further experiments are needed to clarify the entrainment and mixing of the ambient fluid with the current. Comprehensive, and accurate, numerical simulations of these flows should now be possible.
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The Dynamics of Detonation in Explosive Systems*
Vol. 39 (2007), pp. 263–292More LessAbstractThis article reviews advances in modeling condensed-phase explosive detonation waves and their interaction with inerts for precision applications. We describe how constitutive data are obtained for a basic, predictive hydrodynamic model for explosives that subsequently can be studied numerically and analytically. Theory for multidimensional, time-dependent detonation dynamics is reviewed with a focus on freely propagating detonation and the asymptotic theory for quasi-one-dimensional, quasi-steady, detonation shock evolution (detonation shock dynamics). We discuss verification of these theories by direct numerical simulation (DNS) and validation by experiment. We describe a subscale model of detonation that uses an evolution equation to predict detonation dynamics and front states in complex engineering geometries that otherwise could not be computed by DNS. Four areas for future research are identified.
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The Biomechanics of Arterial Aneurysms
Vol. 39 (2007), pp. 293–319More LessAbstractThe formation of an arterial aneurysm is believed to be a multifactorial and predominantly degenerative process, resulting from a complex interplay between biological processes in the arterial wall and the hemodynamic stimuli on the vessel's wall. Once an aneurysm forms, the repetitive pressure and shear stresses exerted by the blood flow on the weakened arterial wall generally, but not always, cause a gradual expansion. As the wall geometry, composition, and strength progressively degrade through the enlargement process, the aneurysm ruptures when the wall of the distended artery fails to support the stresses resulting from the internal blood flow. This review surveys recent progress in this area and provides a critical assessment of the contribution made by hemodynamics studies to the current understanding of the pathogenesis of the disease and to its clinical management.
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The Fluid Mechanics Inside a Volcano
Vol. 39 (2007), pp. 321–356More LessThe style and evolution of volcanic eruptions are dictated by the fluid mechanics governing magma ascent. Decompression during ascent causes dissolved volatile species, such as water and carbon dioxide, to exsolve from the melt to form bubbles, thus providing a driving force for the eruption. Ascent is influenced not only by the nucleation and growth of gas bubbles, but also magma rheology and brittle deformation (fragmentation). In fact, all processes and magma properties within the conduit interact and are coupled. Ultimately, it is the ability of gas trapped within growing bubbles to expand or to be lost by permeable gas flow, which determines whether ascending magmas can erupt nonexplosively. We review and integrate models of the primary conduit processes to show when each process or property dominates and how these interact within a conduit. In particular, we illustrate how and why ascent rate may control eruptive behavior: slowly ascending magmas erupt effusively and rapidly ascending magmas erupt explosively.
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Stented Artery Flow Patterns and Their Effects on the Artery Wall
Vol. 39 (2007), pp. 357–382More LessAbstractStent design and geometry influence the fluid mechanical environment in an artery and hence affect clinical outcomes of restenosis. There is clearly a role for biomechanics in improving current stent designs. This review summarizes some of the work that has been done to address the fluid mechanical aspects of stenting. A variety of computational, experimental, and in vivo approaches have been employed, and the results demonstrate a strong dependence on stent design, as well as effects on hemodynamics in locations of the circulatory system quite removed from the stented segment. There are also important solid mechanical aspects that affect clinical failures of stents that are not summarized here.
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A Linear Systems Approach to Flow Control
John Kim, and Thomas R. BewleyVol. 39 (2007), pp. 383–417More LessAbstractThe objective of this paper is to introduce the essential ingredients of linear systems and control theory to the fluid mechanics community, to discuss the relevance of this theory to important open problems in the optimization, control, and forecasting of practical flow systems of engineering interest, and to outline some of the key ideas that have been put forward to make this connection tractable. Although many significant advances have already been made, many new challenges lie ahead before the full potential of this synthesis of disciplines can be realized.
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Fragmentation
Vol. 39 (2007), pp. 419–446More LessAbstractFragmentation phenomena are reviewed with a particular emphasis on processes that give rise to drops—in the broad sense, the process of atomization. Various observations are brought together to give a unified picture of the overall transition between a compact macroscopic liquid volume and its subsequent dispersion into stable drops. In liquids, primary instabilities always give birth to more or less corrugated ligaments whose breakup determines the shape of the drop-size distribution in the resulting spray. Examples examined here include fragmentation of jets and liquid sheets, formation of spume by the wind blowing over a liquid surface, bursting phenomena upon an impact, and raindrops.
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Turbulence Transition in Pipe Flow
Vol. 39 (2007), pp. 447–468More LessAbstractPipe flow is a prominent example among the shear flows that undergo transition to turbulence without mediation by a linear instability of the laminar profile. Experiments on pipe flow, as well as plane Couette and plane Poiseuille flow, show that triggering turbulence depends sensitively on initial conditions, that between the laminar and the turbulent states there exists no intermediate state with simple spatial or temporal characteristics, and that turbulence is not persistent, i.e., it can decay again, if the observation time is long enough. All these features can consistently be explained on the assumption that the turbulent state corresponds to a chaotic saddle in state space. The goal of this review is to explain this concept, summarize the numerical and experimental evidence for pipe flow, and outline the consequences for related flows.
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Waterbells and Liquid Sheets
Vol. 39 (2007), pp. 469–496More LessAbstractWaterbells result from the impact of a low-viscosity liquid jet (diameter D0, velocity U0) on a solid surface (characteristic length Di) of similar size (Di ∼ D0). Their stationary shape mainly results from the equilibrium between inertia and surface tension. When closed, this shape becomes sensitive to the pressure difference that occurs across the sheet and the bell can become unstable or exhibit stationary cusps. We first review the work done on the shape and stability of waterbells, and then address the case of “special bells,” like swirling bells, polygonal bells, and reverse bells. Finally, we discuss the singular limit of the “flat bell” or liquid sheet.
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Previous Volumes
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Volume 57 (2025)
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Volume 56 (2024)
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Volume 55 (2023)
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Volume 54 (2022)
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Volume 53 (2021)
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Volume 52 (2020)
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Volume 51 (2019)
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Volume 50 (2018)
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Volume 49 (2017)
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Volume 48 (2016)
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Volume 47 (2015)
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Volume 46 (2014)
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Volume 45 (2013)
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Volume 44 (2012)
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Volume 43 (2011)
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Volume 42 (2010)
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Volume 41 (2009)
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Volume 40 (2008)
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Volume 39 (2007)
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Volume 38 (2006)
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Volume 37 (2005)
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Volume 36 (2004)
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Volume 35 (2003)
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Volume 34 (2002)
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Volume 33 (2001)
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Volume 32 (2000)
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Volume 31 (1999)
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Volume 30 (1998)
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Volume 29 (1997)
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Volume 28 (1996)
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Volume 27 (1995)
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Volume 26 (1994)
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Volume 25 (1993)
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Volume 24 (1992)
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Volume 23 (1991)
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Volume 22 (1990)
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Volume 21 (1989)
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Volume 20 (1988)
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Volume 19 (1987)
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Volume 18 (1986)
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Volume 17 (1985)
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Volume 16 (1984)
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Volume 15 (1983)
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Volume 14 (1982)
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Volume 13 (1981)
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Volume 12 (1980)
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Volume 11 (1979)
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Volume 10 (1978)
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Volume 9 (1977)
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Volume 8 (1976)
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Volume 7 (1975)
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Volume 6 (1974)
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Volume 5 (1973)
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Volume 4 (1972)
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Volume 3 (1971)
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Volume 2 (1970)
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Volume 1 (1969)
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Volume 0 (1932)