Extensional rheometry and Brownian dynamics simulations of flexible polymer solutions demonstrate that chain stretching strengthens intermolecular hydrodynamic screening in dilute solutions, but weakens it in semidilute solutions.

The spherically symmetric solute field surrounding a chemically active particle is deformed when the particle sediments or is placed in a shear flow, resulting in velocity enhancement and stresslet reduction, respectively.

Experimental and numerical studies of fingers of Rayleigh-Taylor instabilities in a porous medium find that convection dominates near the tips of the fingers but that lateral diffusion can dominate away from the tips.

The linear response of near-wall turbulence to small-amplitude wall roughness is analyzed. The spectral region where the response is largest is found to be amenable to a simplified quasilaminar analysis.

What would it take to have an underwater vehicle propel itself like a fish or whale? Using a simplified model—an airfoil that pivots back and forth around some axis to produce thrust—the effect on propulsion when the axis of rotation is changed and when springs (passive dynamics) are added to such a system is investigated.

Microparticles flowing through a constricted blood vessel (stenosis) tend to form clusters while red blood cells pass the constriction unhindered. New simulations explain that this striking difference is caused by an interplay between margination and the stenosed geometry.

Swimming at low Reynolds numbers typically requires time-periodic motion that breaks time-reversal symmetry, creating an actual unsteady velocity field around swimming microorganisms. A study of the effect of “unsteadiness” on enhanced diffusivity and tracer displacement statistics takes a step further in considering and modeling realistic microorganisms.

Magnetic and nonmagnetic particles are suspended in liquid metals to obtain a fluid with high magnetic susceptibility, high electrical conductivity, and tunable viscosity. These properties will allow magnetohydrodynamic experiments over a wider parameter range than liquid metals alone.

An extended thermodynamics theory of dissipative dense gases, based on six fields, for those flows where viscous stresses and heat transfer are negligible is presented.

Unsteady motion of a slightly rarefied gas between two parallel plates—caused when one of the plates starts a harmonic oscillation in its normal direction—is analyzed numerically using the compressible Navier-Stokes equations and the correct temperature-jump boundary condition.

Spectra and statistics in compressible isotropic turbulence are studied. In weakly compressible turbulence, the pseudosound mode dominates over the acoustic mode at relatively small scales, and the spectrum of pseudosound velocity exhibits a power-law scaling with the exponent -3.

An investigation shows that confinement of a walking droplet above a rectangular cavity is possible thanks to the Faraday wavefield, overdamped outside the cavity.

The oscillation characteristics of satellite droplets in the beads-on-a-string structure of an Oldroyd-B viscoelastic liquid jet are studied numerically using a one-dimensional model.

An interesting magnetic field geometry for the inertial confinement fusion implosion based on magnetohydrodynamics simulations is proposed.

A modal and nonmodal linear stability analysis of the flow in a microchannel coated with a superhydrophobic material, with a surface topography of arbitrarily aligned microridges, is presented. A new wall-vortex instability is revealed when the ridges are sufficiently inclined with respect to the mean pressure gradient.

A theoretical study identifies the regions that are influential in the amplification of disturbance kinetic energy by harmonic forcing of the flow over shallow cavities.

A reduced two-phase model suitable for industrial uptake is introduced to predict the onset of flow reversal in falling films under countercurrent flow. Analysis of spatiotemporal stability and wave topology shows that vortex distribution plays a crucial role in the incipience of flow reversal.

Planar laser-induced fluorescence is applied simultaneously with particle image/tracking velocimetry and complemented by direct numerical simulations, towards the detailed hydrodynamic characterization of harmonically excited liquid-film flows falling under the action of gravity.

A theoretical analysis of inertial effects in viscous fingering instabilities in a lifting Hele-Shaw cell provides a physical explanation for the dendriticlike patterns observed in experiments where large lifting speeds are used. A generalized Darcy’s law description and a perturbative mode-coupling theory are used to properly account for inertial effects, verifying that inertia induces a mechanism for finger side-branching formation and favors the intensification of finger competition events.

A lubrication-theory-based model of gravity-driven droplet motion on inclined substrates predicts that external shear can either suppress or drive wetting transitions depending on its direction, whereas substrate permeability generally suppresses wetting transitions.

Direct numerical simulations of spray formation in a gas-liquid mixing layer obtain a high-fidelity numerical closeup of the detailed mechanisms of spray formation.

The collapse dynamics of an axisymmetric fluid cavity that wets the bottom of a rotating bucket is studied. The model captures the effect of capillary, gravitational, and centrifugal forces on this converging contact-line flow. Predictions for the collapse time appear as a power law whose exponent compares favorably to experiment.

An intriguing boiling regime is observed from a single bubble oscillating at several 100 kHz on a microheater. Experiments and modeling reveal that pinning, nonspherical collapses with pinch-off, and Marangoni flow lead to many million cycles of clocklike oscillations of the bubble.

An experimental study of the effect of shape on the Quincke phenomenon is presented.

The descending motion of fingerlike plumes is gravitationally driven by a fluid density difference due to a dissolution, mimicking the transport of CO${}_2$-rich dissolution in a saline aquifer.

It is typically presumed that the phoretic motion of particles vanishes at large electrolyte concentration. A new study shows that while this is true for electrophoresis, the diffusiophoretic mobility increases dramatically due to a gradient of steric repulsion between finite-sized ions.

A new study on the interaction between a thin elastic plate and a lubricated liquid layer under a constant end-end displacement shows that the dynamics are affected by the imposed constraints.

Cavitation bubbles in microfluidic gaps can generate strong shear stress and impulsively deform soft objects nearby, such as biological cells. A computational fluid dynamics model allows scientists to analyze the important flow features and explain the strong dependency of deformation on the shape of the objects.

How axisymmetric spheroidal particles rotate in a viscous shear flow is already known. A new study shows that particles with discrete rotational symmetry tumble and spin like spheroids when the rotational axis is contained in a plane of reflection symmetry, but they may spin differently if it is not.

Dependence of turbulence anisotropy on low-order flow descriptions via the proper orthogonal mode basis is detailed for example cases. Truncation based on a fixed level of anisotropy divides the basis into anisotropic and isotropic contributions. Residual error is reduced by a constant correction factor.

Analytic expressions are derived for the eddy diffusivities for generic Stokes times that are exact for shear.

Results from a large direct numerical simulation of channel flow with a friction Reynolds number of 4200 are used to examine the structural and spectral properties of near-wall turbulence.

The Mori-Zwanzig formalism, a concept originating from statistical mechanics, is used to develop non-Markovian subgrid scale models. The form of the closure is imposed by the mathematics of the coarse-graining procedure and is shown to yield accurate predictions in a range of turbulent flows.

A careful, thorough, theoretical study of turbulent stretching behaviors in confined flow is presented.

Direct numerical simulations are conducted to investigate the free rise of isolated, large, deformable bubbles in otherwise homogeneous and isotropic turbulence. The key features of the bubbles’ Lagrangian statistics and of the flow sampled by them are presented.

A theoretical study elucidates the characteristics of the local flow geometry of vortices in an isotropic homogeneous decaying turbulence, using swirlity, sourcity, and the vortical flow symmetry quantity.

The effects of trailing-edge shape on the wake and propulsive performance of a pitching panel are examined. Concave trailing edges delay the natural vortex bending and compression of the wake, whereas convex trailing edges promote wake compression. The trailing edge alters performance significantly.

The equilibrium energy spectrum of the point vortex system is shown to be predictable as a function of the vortex interaction (Hamiltonian) energy.