Experiments with immersed drops spreading on a surface or with two drops coalescing find that the contact diameter obeys a power law in time and in the internal and external viscosities.

In an investigation of how drops merging on a nonwetting surface jump off the surface, the takeoff velocity is measured and modeled.

Particle velocity fluctuations in a large-scale circulating fluidized bed are observed to be anisotropic and non-Maxwellian. Interfacial drag acting on high-density configurations lead to excursions resulting in Levy flight of particles.

Scattering trajectories for a swimmer interacting with a particle are simulated in Stokes flow, varying the size of the particle from much smaller than to much larger than the swimmer. The particle deflects the swimmer’s path, which can lead to a larger particle having a larger net displacement.

A rotating helical pump actively stretches nearby polymers and draws them inwards as demonstrated in Stokesian dynamics simulations. The effect of such an interaction hinders the helix, increasing the amount of work required to maintain constant rotation.

The asymptotic far-field behavior of macroscopic quantities in a problem of slow uniform rarefied gas flow past a sphere is investigated for the purpose of acquiring a function occurring in the second-order drag. The thermal force in the problem of thermophoresis of a sphere is also discussed.

The influence of inclination angle on the turbulent liquid metal convection in a cylindrical cell under an axial temperature gradient is studied numerically. The applicability of idealized thermal boundary conditions for modeling experiments on liquid sodium convection is examined.

A thermal boundary layer equation that includes fluctuations is solved using a relation between the eddy thermal diffusivity and the stream function, and a closed-form expression for the mean temperature profiles in turbulent Rayleigh-Bénard convection is obtained for fluids with a general Prandtl number .

Large-scale features in rotating convection can take the form of either jets or coherent vortices. Numerical simulations of horizontally anisotropic planar rotating convection reveal the interaction between jets and vortices and show how these typically co-exist.

Vesicle motion through a narrow channel with fluid resistance is studied with lubrication theory and lattice Boltzman simulations. We find two dimensionless parameters that characterize the motion and that multistable dynamics, in which a vesicle may move in either direction, are possible.

We present the results of a numerical investigation of droplets walking in a harmonic potential. Particular attention is given to delineating the parameter regimes in which periodic and chaotic trajectories arise, and double quantization in energy and angular momentum emerges.

A spherical drop charged beyond its Rayleigh limit ejects a significant fraction of its charge as a jet. Coupled hydrodynamics and electrostatics are used to find the charge loss in the low Re limit. Simulations show this is 39% of the initial charge, within the known experimental range of 20–50%.

The impact of surfactant redistribution along a droplet surface on the deformation and suspension rheology of a dilute droplet emulsion suspended in a linear flow field is analyzed. The study find that an increase in surfactant convection augments droplet deformation and emulsion effective viscosity.

We show that the critical point of a static pendent drop pinned at a curve under volume or pressure control is bounded independent of the curve symmetry. If the curve is symmetric and the base drop shape known, the critical points for symmetric or asymmetric instability are found.

Image systems for Stokes flow singularities outside a drop covered with an incompressible surfactant are derived. They are used in finding the mobility matrix for two surfactant-laden drops of arbitrary sizes and the velocity of a microorganism outside a surfactant-covered drop.

The formation of the mushroomlike jet emerging after droplet coalescence is deciphered by studying the growth and detachment of the main vortex ring. A Reynolds number calculated based on the main vortex ring is shown to provide a unified formation criterion for such internal jets.

The interaction of vortices with a magnetic field is studied using both theoretical scaling arguments and numerical simulations. Even very weak background fields can be amplified to such a strength that the vortices are severely disrupted or even destroyed by the Lorentz force.

Spatially localized stochastic forcing generates turbulent dynamics in a 2D fluid with a uniform background vorticity gradient, enabling a study of the turbulent transport of kinetic energy.

An experimental study of low-aspect-ratio rectangular wings in cross flow shows that the reorganization of vortex flow on the wing plays a key role in initiating “roll stall” at angles of attack of sustained/increasing lift.

Many fluid systems consisting of an assembly of multiple but identical elements exhibit collective and synchronized motion involving groups of locked-in units. A computational framework for this type of fluid system with examples from hydrodynamic stability and turbomachinery is presented.

A linear stability analysis of the mean flow of turbulent channels with temperature-dependent density and viscosity predicts modified energy growth rate and threshold for secondary instability of streaks consistent with direct numerical simulation observations. Semilocal scaling parametrizes the effect of properties.

A numerical method for the computation of unstable limit-cycle flows is presented. This technique, straightforward to implement, filters nonperiodic components with a time-delayed feedback. It is shown for the examples of an axisymmetric forced jet subject to pairing and a 3D lid-driven cavity.

A study on the draw resonance instability in Newtonian fiber spinning and the influence of inertia, gravity, and surface tension is presented. The results are evaluated using stability maps of highly practical relevance and various dynamical regimes are revealed and discussed.

The local mass flux around a CO${}_2$ gas bubble dissolving against a wall are experimentally determined and an analytical model is presented. Rayleigh number is shown to be crucial in estimating the condensing or evaporating rates of bubbles or droplets deposited on a flat surface.

Stokes flow solutions are studied in the corner made by a fluid-fluid interface. The existence of an infinite series of Moffatt vortices is examined.

In an electrolyte solution near ion-selective surfaces in an external electric field we theoretically find a thermoelectrokinetic instability and study it numerically. The instability comes from nonuniformity of the electric current and conductivity in long channels with good thermal insulation.

A simple continuum model to study the fingering instability in systems of micro-particles rotating parallel to a floor is developed. Analytical results are in agreement with the simulations and experiments, and are used to extract the physical mechanisms that trigger the instability.

Analyzing grain motion statistics shows that, in the presence of turbulence, it is not possible to unambiguously distinguish between mobile and static grains near the onset of sediment transport. Instead we treat these grains together and fit their statistics with a two-phase mixture model.

The time it takes porous particles, like marine snow, to reach the ocean floor depends on the density of the water they encounter. The density of a particle’s inner fluid changes on a diffusive time scale, which can slow its progress to a crawl. A new study quantifies the resulting delays numerically.

A nonmonotonic decay in contact angle was observed in drying suspensions of concentrated film-forming latexes. Heterogeneity in film topologies is associated with particle packing at the droplet edge. The process is quantitatively modeled by considering dilational stresses in a viscoelastic solid.

A method to coarse-grain the results of resolved simulations is described and used to demonstrate the presence of continuity waves in the simulations of 500–2000 particles suspended in an upward fluid flow. The results agree very well with the standard continuum theory of kinematic waves.

The role of incomplete mixing through an idealized two-dimensional heterogeneous porous medium is studied using a Lagrangian reactive particle tracking method. Velocity-gradient-based flow deformation metrics are considered and connections are made to conservative transport.

A numerical study of decaying wall-bounded turbulence is made by stopping the forcing in a Taylor-Couette system. The decay progressively exhausts all modes through which perturbations grow, from most unstable to least unstable until a final stage of self-similar viscous decay is reached.

Kolmogorov’s theory gives predictions for the inertial scales of turbulent flows but not for the large scales. Direct numerical simulations and analytic derivation are used to investigate the spatiotemporal properties of large scales for flow solutions of Navier-Stokes and truncated Euler equations.

Laboratory experiments of turbulence of non-Newtonian fluids reveal that the fully developed turbulence of Newtonian fluids in a precessing sphere is sustained by an energy cascading process.

Three commonly used methods of energy injection are tested in simulations of homogeneous, incompressible magnetohydrodynamic turbulence without a mean magnetic field, showing, among other things, that the cross helicity is sensitive to the forcing function.

Numerical simulations have revealed that mean flow directed to the rotation axis is generated against the turbulent diffusion only in the case of both inhomogeneous helical forcing and system rotation. The origin of the phenomenon is examined in terms of the Reynolds-stress transport equation.

New work characterizes the chaotic nature of isotropic turbulence using Lyapunov exponents and determines how they scale with Reynolds number. The scaling results suggest that instabilities could act on sub-Kolmogorov scales at sufficiently high Reynolds numbers.

The near wake of a multiscale array of bars is studied in search of features of multiscale-generated turbulence. Additional velocity modes are found on top of the regular sheddings close to the various wakes’ intersections. The energy budget of the triple-decomposed velocity yields further insight.

Wall curvature effect for an impinging jet flow is investigated. The concave curvature is found to reduce the heat transfers at the wall. A detailed analysis of the mechanisms driving the heat transfers shows the impact of the stabilization effect present in the wall jet over the curved surface.

Anisotropic permeable surfaces are proposed to reduce turbulent skin friction. The apparent streamwise slip induced reduces drag, while the spanwise one increases it. Transpiration can trigger the appearance of Kelvin-Helmholtz-like rollers, which limit the performance of the surface.

The modification due to weak fluid compressibility of the speed of travel of the incompressible point vortex streets of von Karman is determined in analytical form as a function of the street aspect ratio.

Numerical simulations of the decay of two-dimensional turbulence find new scalings for the distribution of the sizes of vortices and their strength, such that the time for vortices to cross the intervortex separation is independent of their size.

Higher harmonic internal waves are generated at wave intersections and critical points of oscillating bodies, with higher amplitudes at steeper slopes and amplitude increase due to focusing for axisymmetric bodies. The horizontal structure of the $n$th harmonic corresponds to multipole order $2^n$.

Water surface deformation is reconstructed by stereoscopic imaging to develop a high-order statistical analysis of randomly forced turbulent gravity waves. Resonant wave coupling is investigated and laboratory data compared to field measurements in the Black Sea.

Physical effects scale differently with size. As a necessary preliminary step toward geophysically significant extrapolations, an experimental and numerical study of the scale effects in internal wave attractors in linear and nonlinear regimes is made, showing two different scalings for the beam width.

A nonlinear fractional wave equation for 2D sound waves at interfaces is derived from first principles. Numerical solutions of the equation reproduce experimental key features, namely an abrupt increase in range accompanied by a slight increase in wave velocity at a threshold excitation amplitude.