Volumes of this journal typically include one or two historical articles, many of which celebrate the life and impact in fluid mechanics of a recently deceased contributor to the field. The Editorial Committee recently stepped beyond this model to examine whom might have been missed over the years. Naturally, even when a candidate is identified, the passing of time makes it hard to find authors with

If one opens today a textbook on fluid mechanics, it seems that whereas French scientists of the eighteenth and nineteenth centuries are frequently mentioned, those from more recent times occur rarely; in particular, French contributions to the major breakthroughs of the first half of the twentieth century (boundary layers and turbulence) would appear quite modest. However, study of contemporary documents

Colloid-sized particles (10 nm–10 μm in characteristic size) adsorb onto fluid interfaces, where they minimize their interfacial energy by straddling the surface, immersing themselves partly in each phase bounding the interface. The energy minimum achieved by relocation to the surface can be orders of magnitude greater than the thermal energy, effectively trapping the particles into monolayers, allowing

Gusts of moderate and large magnitude induce flow separation and other complexities when they interact with the lifting surfaces of air vehicles. The presence of these nonlinear gusts are becoming ubiquitous in twenty-first-century air vehicles, where the classic potential flow–based methodologies applied in the past may no longer be valid. In this review, we define the parameter space for the presence

The interactions of textiles with moisture have been thoroughly studied in textile research, while fluid mechanists and soft matter physicists have partially investigated the underlying physics phenomena. A description of liquid morphologies in fibrous assemblies allows one to characterize the associated capillary forces and their impact on textiles, and to organize their complex moisture transport

Taking a small step away from Newtonian fluid behavior creates an explosion in the range of possibilities. Non-Newtonian fluid properties can achieve diverse flow objectives, but the complexity introduces challenges. We survey useful rheological complexity along with organizing principles and design methods as we consider the following questions: How can non-Newtonian properties be useful? What properties

The pervasiveness of unmanned air vehicles (UAVs), from insect to airplane scales, combined with active flow control maturity, has set the scene for vehicles that differ markedly from present-day configurations. Nano and micro air vehicles, with characteristic Reynolds numbers typically less than 105, rely on periodically generated leading-edge vortices for lift generation, propulsion, and maneuvering

Inkjet printing is the most widespread technological application of microfluidics. It is characterized by its high drop productivity, small volumes, and extreme reproducibility. This review gives a synopsis of the fluid dynamics of inkjet printing and discusses the main challenges for present and future research. These lie both on the printhead side—namely, the detailed flow inside the printhead, entrained

As a fundamental topology-transforming event, reconnection plays a significant role in the dynamics of plasmas, polymers, DNA, and fluids—both (classical) viscous and quantum. Since the 1994 review by Kida & Takaoka, substantial advances have been made on this topic. We review recent studies of vortex reconnection in (classical) viscous flows, including the physical mechanism, its relationship to turbulence

Every year flood events lead to thousands of casualties and significant economic damage. Mapping the areas at risk of flooding is critical to reducing these losses, yet until the last few years such information was available for only a handful of well-studied locations. This review surveys recent progress to address this fundamental issue through a novel combination of appropriate physics, efficient

The current generation of axial turbomachines is the culmination of decades of experience, and detailed understanding of the underlying flow physics has been a key factor for achieving high efficiency and reliability. Driven by advances in numerical methods and relentless growth in computing power, computational fluid dynamics has increasingly provided insights into the rich fluid dynamics involved

Dynamic mode decomposition (DMD) is a factorization and dimensionality reduction technique for data sequences. In its most common form, it processes high-dimensional sequential measurements, extracts coherent structures, isolates dynamic behavior, and reduces complex evolution processes to their dominant features and essential components. The decomposition is intimately related to Koopman analysis

Breaking waves modulate the transfer of energy, momentum, and mass between the ocean and atmosphere, controlling processes critical to the climate system, from gas exchange of carbon dioxide and oxygen to the generation of sea spray aerosols that can be transported in the atmosphere and serve as cloud condensation nuclei. The smallest components, i.e., drops and bubbles generated by breaking waves

This review is motivated by the fast progress in our understanding of the physics of particle-laden turbulence in the last decade, partly due to the tremendous advances of measurement and simulation capabilities. The focus is on spherical particles in homogeneous and canonical wall-bounded flows. The analysis of recent data indicates that conclusions drawn in zero gravity should not be extrapolated

Idealized simulations of the tropical atmosphere have predicted that clouds can spontaneously clump together in space, despite perfectly homogeneous settings. This phenomenon has been called self-aggregation, and it results in a state where a moist cloudy region with intense deep convectivestorms is surrounded by extremely dry subsiding air devoid of deep clouds. We review here the main findings from

Global differences of temperature and buoyancy flux at the ocean surface are responsible for small-scale convection at high latitudes, global overturning, and the top-to-bottom density difference in the oceans. With planetary rotation the convection also contributes to the large-scale horizontal, geostrophic circulation, and it crucially involves a 3D linkage between the geostrophic circulation and

Liquid-infused surfaces (LISs) are composite solid–liquid surfaces with remarkable features such as liquid repellency, self-healing, and the suppression of fouling. This review focuses on the fluid mechanics on LISs, that is, the interaction of surfaces with a flow field and the behavior of drops on such surfaces. LISs can be characterized by an effective slip length that is closely related to their

Abstract

The last decade has seen a significant increase in the number of studies devoted to wave turbulence. Many deal with water waves, as modeling of ocean waves has historically motivated the development of weak turbulence theory, which addresses the dynamics of a random ensemble of weakly nonlinear waves in interaction. Recent advances in experiments have shown that this theoretical picture is too idealized

Long-lasting emission from femtosecond excitation of nitrogen-based flows shows promise as a useful mechanism for a molecular tagging velocimetry instrument. The technique, known as femtosecond laser electronic excitation tagging (FLEET), was invented at Princeton a decade ago and has quickly been adopted and used in a variety of high-speed ground test flow facilities. The short temporal scales offered

Thin film flows, whether driven by gravity, surface tension, or the relaxation of elastic boundaries, occur in many natural and industrial processes. Applications span problems of oil and gas transport in channels to hydraulic fracture, subsurface propagation of pollutants, storage of supercritical CO2 in porous formations, and flow in elastic Hele–Shaw configurations and their relatives. We review

Reliable full-scale prediction of drag due to rough wall-bounded turbulent fluid flow remains a challenge. Currently, the uncertainty is at least 10%, with consequences, for example, on energy and transport applications exceeding billions of dollars per year. The crux of the difficulty is the large number of relevant roughness topographies and the high cost of testing each topography, but computational

We review studies of levitating droplets over liquid–gas interfaces and dry solid surfaces with a focus on the physical mechanisms of levitation under different conditions. A fascinating physical phenomenon of self-organization of levitating droplets into large arrays is described and explanations for this unusual behavior are reviewed. Closely related topics of nonisothermal flotation and levitation

The use of X-ray flow visualization has brought a powerful new tool to the study of multiphase flows. Penetrating radiation can probe the spatial concentration of the different phases without the r...

For an infectious disease such as the coronavirus disease 2019 (COVID-19) to spread, contact needs to be established between an infected host and a susceptible one. In a range of populations and in...

From intracellular protein signaling to embryonic symmetry-breaking, fluid transport ubiquitously drives biological events in living systems. We provide an overview of the fundamental fluid mechani...

This review surveys the dramatic variations in wake structures and flow transitions, in addition to body forces, that appear as the motion of bluff bodies through a fluid occurs increasingly closer...

Transient growth and resolvent analyses are routinely used to assess non-asymptotic properties of fluid flows. In particular, resolvent analysis can be interpreted as a special case of viewing flow dynamics as an open system in which free-stream turbulence, surface roughness, and other irregularities provide sources of input forcing. We offer a comprehensive summary of the tools that can be employed

Placing mechanical devices into fast-moving tidal streams to generate clean and predictable electricity is a developing technology. This review covers the fundamental fluid mechanics of this applic...

This review examines large eddy simulation (LES) models from the perspective of their a priori statistical characteristics. The most well-known statistical characteristic of an LES subgrid-scale mo...

Wall-bounded turbulence exhibits patterns that persist in time and space: coherent structures. These are important for transport processes and form a conceptual framework for important theoretical ...

Oceanic lee waves are generated in the deep stratified ocean by the flow of ocean currents over sea floor topography, and when they break, they can lead to mixing in the stably stratified ocean int...

The removal of unwanted entities or soiling material from surfaces is an essential operation in many personal, industrial, societal, and environmental applications. The use of liquid cleansers for ...

Understanding how turbulence leads to the enhanced irreversible transport of heat and other scalars such as salt and pollutants in density-stratified fluids is a fundamental and central problem in ...

Extreme events in fluid flows, waves, or structures interacting with them are critical for a wide range of areas, including reliability and design in engineering, as well as modeling risk of natura...

Sediment-laden gravity currents, or turbidity currents, are density-driven flows that transport vast quantities of particulate material across the floor of lakes and oceans. Turbidity currents are ...

A viscous solvent laminar flow may be strongly modified by the addition of a tiny amount of long polymer molecules, resulting in a chaotic flow called elastic turbulence (ET). ET is attributed to p...

This review focuses on Leonardo da Vinci's work and thought related to fluid mechanics as it is presented in a lifetime of notebooks, letters, and artwork. It shows how Leonardo's remaining works o...

Complex fluids exist in nature and are continually engineered for specific applications involving the addition of macromolecules to a solvent, among other means. This imparts viscoelasticity to the...

Nanofluidics has firmly established itself as a new field in fluid mechanics, as novel properties have been shown to emerge in fluids at the nanometric scale. Thanks to recent developments in fabri...

We present a brief account of Anatol Roshko's research and educational contributions to fluid mechanics, focusing on the spirit of his transformative ideas and legacy.

David J. Benney (1930–2015) was an applied mathematician and fluid dynamicist whose highly original work has shaped our understanding of nonlinear wave and instability processes in fluid flows. Thi...

A spectacular resurgence of interest in the topic of ocean wave/sea ice interactions has unfolded over the last two decades, fueled primarily by the deleterious ramifications of global climate chan...

Rigid or deformable bodies moving through continuously stratified layers or across sharp interfaces are involved in a wide variety of geophysical and engineering applications, with both miscible an...

Since the Annual Review of Fluid Mechanics review of mushy layers by Worster (1997), there have been significant advances in the understanding of convective processes in mushy layers. These advance...

Shear thickening is the increase of the apparent viscosity as shear rate or shear stress increases. This phenomenon is pronounced in concentrated (dense) suspensions of both colloidal-scale and lar...

Buoyant plumes form when glacial ice melts directly into the ocean or when subglacial meltwater is discharged to the ocean at depth. They play a key role in regulating heat transport from the ocean to the ice front, and in exporting glacial meltwater to the open ocean. This review summarises current understanding of the dynamics of these plumes, focussing on theoretical developments and their predictions

Turbulent flows in porous media occur in a wide variety of applications, from catalysis in packed beds to heat exchange in nuclear reactor vessels. In this review, we summarize the current state of...

Acoustic tweezers powerfully enable the contactless collective or selective manipulation of microscopic objects. Trapping is achieved without pretagging, with forces several orders of magnitude lar...

Metal films of nanoscale thickness, deposited on substrates and exposed to laser heating, provide systems that involve several interesting multiphysics effects. In addition to fluid mechanical aspe...

Soft porous solids can change their shapes by absorbing liquids via capillarity. Such poro-elasto-capillary interactions can be seen in the wrinkling of paper, swelling of cellulose sponges, and mo...

The laws of wetting are well known for drops on rigid surfaces but change dramatically when the substrate is soft and deformable. The combination of wetting and the intricacies of soft polymeric in...

Density variations in fluid flows can arise due to acoustic or thermal fluctuations, compositional changes during mixing of fluids with different molar masses, or phase inhomogeneities. In particul...

Experiments and numerical simulations have shown that turbulence in transitional wall-bounded shear flows frequently takes the form of long oblique bands if the domains are sufficiently large to accommodate them. These turbulent bands have been observed in plane Couette flow, plane Poiseuille flow, counter-rotating Taylor–Couette flow, torsional Couette flow, and annular pipe flow. At their upper Reynolds

Quantifying submillimeter flows using optical diagnostic techniques is often limited by a lack of spatial resolution and optical access. This review discusses two super-resolution imaging technique...

The ability of some species of owl to fly in effective silence is unique among birds and provides a distinct hunting advantage, but it remains a mystery as to exactly what aspects of the owl and it...

Fluid-structure interaction is ubiquitous in nature and occurs at all biological scales. Immersed methods provide mathematical and computational frameworks for modeling fluid-structure systems. These methods, which typically use an Eulerian description of the fluid and a Lagrangian description of the structure, can treat thin immersed boundaries and volumetric bodies, and they can model structures

The term “bioconvection” describes hydrodynamic instabilities and patterns in suspensions of biased swimming microorganisms. Hydrodynamic instabilities arise from coupling between cell swimming beh...

The field of fluid mechanics is rapidly advancing, driven by unprecedented volumes of data from field measurements, experiments and large-scale simulations at multiple spatiotemporal scales. Machine learning offers a wealth of techniques to extract information from data that could be translated into knowledge about the underlying fluid mechanics. Moreover, machine learning algorithms can augment domain

Many electrochemical and microfluidic systems involve voltage-driven transport of ions from a fluid electrolyte toward an ion-selective interface. These systems are governed by intimate coupling be...