Prior work on curvature capillary attraction for colloids on fluid interfaces is extended, and the concept of curvature capillary repulsion is introduced.

The mechanisms that underlie the interactions between the inner and outer regions of wall-bounded turbulence are considered, and their effect on the near-wall turbulence intensity is discussed.

We investigate effects of stratification on the hydrodynamics of settling particles, rising drops, and small organism motion. Density stratification leads to enhanced clustering in a suspension of particles/drops and affects the flow field, energy expenditure, and detectability of small organisms.

Low-dimensional models of experimental and simulation data for a complex supersonic jet are fused to reconstruct time-dependent coefficients. Data fusion techniques use the strengths of experimental statistical ensembles and the time resolution of large-eddy simulation to provide a more complete view of the flow.

Some semi-aquatic insects, such as water striders and springtails, can jump off the water surface by exploiting the interfacial tension to escape from predators. We present a theoretical framework to analyze and predict the jumping of those insects.

The paper illustrates the potential of advanced optical metrology combined with DNS for the study of near-wall turbulence including the critical case of a turbulent boundary layer in a mild adverse pressure gradient. Insights obtained point towards significant improvements in turbulence modelling.

Professor Stone discusses some aspects of his research group’s recent studies related to multiphase flows and the flows of complex fluids for which he received the APS Fluid Dynamics Prize.

Analysis of many observations of individual red blood cells entering a microfluidic constriction yields a nonlinear elastic modulus of 60 $\mu$N/m, an order of magnitude larger than moduli found previously in the linearized regime.

Three-dimensional computer simulations reveal that tapering the thickness of a fin enhances propulsion efficiency and enables high thrust and swimming velocity for a wide range of actuation frequencies.

Using frequency modulation atomic force microscopy (FM-AFM), dissipation is studied in the neighborhood of a pinned contact line on an oscillating nano-fiber.

Two-dimensional simulations of a granular flow at constant normal stress study the effects of varying the particle stiffness and the inertia number on the rheology, the packing fraction, and the fluctuations of local shear rate.

Turbulence is forced at small scales by applying an alternating magnetic field to magnetic particles within the fluid. Measuring the increase in temperature, the dissipation is found to be proportional to the number of particles.

When helicity is made sign-definite by retaining only specific triadic interactions, an inverse energy cascade develops towards large scales in $k^{-5/3}$, with a direct helicity cascade towards small scales in $k^{-7/3}$.

A pair of vesicles sheared between two parallel walls is in an equilibrium state with constant separation increasing with interwall distance. Ordered vesicle suspension is observed in this state. Ordering leads to a decrease of the normalized suspension viscosity with increasing concentration.

Geometric features of the premixed flame front in turbulence are investigated using relatively simple propagating surfaces. The study is also aimed at partially bridging the gap between the Lagrangian studies in nonreacting turbulence and in turbulent premixed combustion.

The first systematic study of the effect of polymer concentration, from dilute to entangled, on the elastic instability and elastic turbulence, with information about velocities, torques, and pressures, their power spectra and correlation and structure functions.

The sedimentation of a rigid, spherical particle in a cross sheared elastic fluid is studied. By increasing the shear rate (shear Weissenberg number, Wi), the growth of viscoelastic wake structures, resembling wings, is observed, which are linked to a dramatic decrease in the particle mobility.

Convection is a key process in fuel cells, hence it is vital to describe it properly. A comparison to published data establishes constraints to competing formulations. The contribution of convective transport in porous media is shown to be fundamental in the prototype’s performance.

Boundary layer (BL) equations imply that in all BL-determined Grossmann-Lohse regimes of natural thermal convection, the relation Nu$\sim$Re${}^{1/2}$Pr${}^{1/2}$ between the Nusselt, Reynolds, and Prandtl numbers hold, which leads to Nu$\sim$Pr${}^0$Ra${}^{1/3}$, Re$\sim$Pr${}^{-1}$Ra${}^{2/3}$ for Pr$\gg$1.

A study using optical high speed imaging shows that droplet dynamics and contact times of water droplets impacting vibrating superhydrophobic surfaces depend on the vibration frequency, phase at impact, and amplitude of vibration. Contact times can be greater or smaller than the theoretical contact time on a nonvibrating surface.

A hydrodynamic analog of the Talbot or self-imaging effect is observed on the surface of a vertically shaken fluid bath when a periodic row of pillars protrudes from the surface. The self-images are used to trap bouncing and walking droplets.

The counter-intuitive destabilization of shear flow by surface tension is rationalized in terms of the interaction in a distance between interfacial counter-propagating vorticity waves on a Taylor-Caulfield setup. Interestingly the flow can be unstable even in the absence of stratification.

The three-dimensional characteristics of viscous fingering of miscible fluids in porous media are investigated using a microfocused x-ray CT scanner.

Solutal advective flow induced in a horizontal shallow layer by the initial longitudinal steplike density distribution becomes unstable when the solutal Péclet number exceeds the critical value. The Péclet number uniquely determines the spatiotemporal characteristics of the secondary flow.

The impact of partial miscibility on viscous fingering dynamics is studied, demonstrating that the coupling between viscous and compositional effects lead to a rich set of displacement patterns. Snapshots of mixture concentration at various initial compositions and log-mobility ratios are shown.

A study of flow in a thin liquid film in a bilayer system over a heated, asymmetric corrugated solid surface, underneath an isothermal hydrophobic plate shows that the presence of a hydrophobic plate enables a sustained Marangoni flow in narrow systems where it would be impossible in its absence.

Most continuum models of two-phase flows through porous media have been developed for low permeability structures, with capillary and Bond numbers lower than one. When the permeability is large, our results show that standard approaches fail to capture momentum exchanges between phases.

Using experiment, simulation, and analytical balances, the types of configurations and dynamics that arise from a rotating flexible DNA-linked particle chain are studied as a function of viscous, magnetic, and elastic forces on the chain. Complex dynamical modes like coiling and wagging are observed.

The resistance to the motion of a cylinder near a slippery wall is calculated in the lubrication limit. The properly scaled resistance depends only upon the ratio of slip length to cylinder-wall clearance. The companion problem of a slippery cylinder reveals a symmetry relating the two problems.

Active nematics, e.g., liquid crystals filled with living bacteria, are known to spontaneously flow in large systems. A new study shows that in some geometries, spontaneous flow can occur in arbitrarily small systems and that such flows can power microfluidic pumps with no moving parts.

Fluttering motions like those of falling leaves had been mostly studied in nonconfined fluids and/or at large Reynolds numbers. We study confined cylinders sedimenting between closely spaced walls: fluttering retains similar characteristics although both drag and viscous forces increase drastically.

We study settling of inertial particles in homogeneous turbulence. Under two-way coupling effects direct numerical simulations show that the local collective backward-force exerted by the particles on the fluid make the particles and fluid fall together.

Schlieren measurements of an air bubble sliding under a heated inclined surface reveal an intricate wake structure that is difficult to observe using alternative techniques. Image tracking is also used to extract the dynamics of the gas-liquid interface to augment these visualizations.

Numerical simulations are used to study the effect of deformability of sub-Kolmogorov dispersed bubbles on the drag induced by a carrier fluid in a two-phase Taylor-Couette flow. The simulations are performed by coupling a subgrid deformation model with two-way coupled Euler-Lagrangian tracking.

Three-dimensional numerical simulations are used to study the dynamics of an eccentric nested liquid droplet of three immiscible fluids. An orbiting trajectory is found if the inner drop offset is in the plane of shear, and a drift away from center is found for an offset along the vorticity direction.

Electrophoretic mobility of single colloids under an ac electric field is studied experimentally and theoretically. At low electric field frequencies, we observe a decay of the mobility as the frequency increases. The theoretical model is in good agreement with the observations.

Improved heat transfer technologies are essential for improving overall energy efficiency. Fluid flows optimal for heat transfer in a 2D channel are calculated, and heat transfer proportional to the energy budget to the 1/5 power is obtained—an improvement over the classical 1/6 scaling law.

Dye flowing through a porous medium is observed in experiments to form sheets which stretch, fold, and overlap at random, leading to a Gamma function probability distribution of concentration, and Beta distributions for their mixing ratio.

A horizontally integrated model for bubble plumes in stratified environments, including inlet conditions, finds that the maximum plume momentum height cannot be identified with the neutral buoyancy height, which it is always less than. These results are in agreement with existing observations.

Log-layer mismatch in wall-modeled LES is shown to be a result of the unphysical correlation between the fluctuating wall-shear stress and the velocity fluctuations at the first off-wall grid point. A new remedy is proposed, which would be better suited for complex geometry and unstructured grids.

Vortex packet signatures were identified from PIV data downstream of single arrays of narrowly spaced cylinders. Downstream of tall cylinders, packets were found to recover from bottom up, while for shorter cylinders, packets appeared to recover from top down.

The impact of large-scale advection on smaller-scale velocity fluctuations in turbulent flows is investigated using an analysis of the Navier-Stokes equations based on a spatial filtering technique. Analytical results are compared to direct numerical simulations of fully developed turbulence.

For a particle in a turbulent flow in stationary conditions, kinetic energy is lost faster than it accumulates. This time asymmetry depends on the Reynolds number of the flow. Here we show how the Reynolds number dependence of Lagrangian irreversibility can be predicted by the multifractal model.

A modification of the classical Turner two-layer-stratified grid experiment is presented. The system is capable of maintaining a steady state and specifying the Richardson number and the entrainment velocity independently. The analytical model developed is in good agreement with the experiment.

The effect of forcing phase difference on active lock-on phenomena is studied by using an extended linear theory to predict the centers of various lock-on regimes and by simulating a synthetic-jet-pair controlled cylinder flow system to determine the shape and size of each lock-on regime.

A linear stability analysis on the dynamics of azimuthally symmetric swirling flows and the emergence of steady rotating polygons is presented. The different behaviors of the system are discussed as an interaction between horizontal inner centrifugal edge waves and outer vertical gravity edge waves.

Theoretical predictions and oceanic observations of stratified turbulence give a vertical energy spectrum that has thus far escaped reproduction in experiments or simulations. This spectrum is recovered in direct numerical simulations by filtering out small-scale isotropic motions.

Entrainment in stably stratified mixing layers is studied in relation to the turbulent/nonturbulent interface with Eulerian and Lagrangian statistics from direct numerical simulations. The characteristics of entrainment change as the buoyancy Reynolds number decreases and the flow begins to layer.