In elastic wake in a creeping flow of a dilute polymer solution past two widely separated cylinders, two symmetry-breaking instabilities related to mirroring and time-reversal are found above critical Weissenberg numbers. Vorticity growth up to the cylinder separation length is observed.

Microparticles are quickly and efficiently sorted by size through the action of an oscillating bubble attached to a microfluidic channel. Experimental observations and a quantitative theory of general particle deflections near oscillating interfaces are presented.

Experiments show complete axial separation of multicomponent granular mixtures in laterally shaken ratchet-shaped channels. Extensive experiments and simulations reveal that axial segregation is driven by a new mechanism that relies on strikingly gentle, average interfacial pressure gradients.

A planar shock wave impacting on a cylindrical density interface results in turbulence with different power-law scalings.

In high-resolution direct numerical simulations, it is found that, independent of the anisotropic content of the energy containing eddies, small-scale turbulent fluctuations recover isotropy and universality faster than previously reported.

Weak wave turbulence theory gives statistics of an ensemble of interacting dispersive waves. Using the Majda-McLaughlin-Tabak model, theory predictions are found to be accurate in the weakly nonlinear regime. Multifractal and intermittent dynamics, as in fluid turbulence, occurs at large nonlinearity.

Experiments show that actuation waveform has a dramatic impact on the performance and wake of an unsteady propulsor. The thrust and power scale with the peak lateral velocity of the foil. The wake transitions to a different state as waveforms become more squarelike.

Concentrating the energy release of a medium in spatially discrete pockets affects detonation waves. In a numerical study, detonations are observed to propagate at average speed as much as 10% greater than the corresponding Chapman-Jouguet speed of the homogenized medium due to nonequilibrium at the effective sonic plane.

Complex fluids generate different types of flow instabilities with increasing flow rate under inertialess flow conditions in a flow focusing device.

A general model for a nematic electrolyte with spatially varying tensor order parameter is derived based on Onsager’s variational principle. The model is verified by considering liquid crystal-enabled electro-osmotic flow around a stationary spherical dielectric particle with homeotropic anchoring.

Simulations of viscoelastic flows through model porous media show that flow structures are completely different for symmetric and asymmetric configurations at the same porosity. Most energy dissipation is occurring in shear-dominated, not extensional-flow-dominated, regions of the flow domain.

Structure functions and PDFs of increments of the compressible velocity component and thermodynamic variables in compressible isotropic turbulence are studied. The relative scaling exponent of the structure functions saturates with increase of the order, due to the effect of shocklets.

Evaporation is crucial in diverse fields like botany, climatology, or colloids. While for small drops, evaporation is well described by vapor diffusion, a flow driven by the density difference between vapor and ambient air causes natural convection for larger drops, increasing the evaporation rate.

A combined experimental and theoretical investigation of interacting pairs of walking droplets shows that they may lock into circular orbit. The walkers are found to adapt their impact phase according to the local wave height, an effect that stabilizes orbiting bound states.

“Singing of a cavitating tip vortex” (SCTV) occurs in the transition process between strong and weak tip vortex cavitations. It is shown that the generation mechanism of SCTV is one kind of resonance of a cylindrical bubble at its natural frequency.

Numerical simulations of bubble collapse show that the combined effects of air chemistry at high temperature and a stiffened gas equation of state for air at high pressures lead to significantly lower peak temperature and pressure during the evolution.

A new study shows that fluid-flow-driven dynamos benefit from periodic perturbations of the large-scale velocity field providing energy for magnetic field generation. This relies on azimuthal field eigenmode coupling and can qualitatively be explained with Floquet theory as in periodically perturbed mechanical systems.

The stability of the Taylor-Couette flow with a stationary outer cylinder is sensitive to the radial temperature gradient. A numerical investigation shows that the nature of the bifurcation and the consequent heat transfer depend significantly on the heating direction as well as on the diffusive properties of the fluid.

Generation of magnetic field in a buoyancy-driven conducting fluid filling a rotating spherical shell is an idealized model of the Earth’s dynamo. A numerical investigation demonstrates that for an appropriate parameter range there is a hysteresis between the magnetic and the nonmagnetic field solutions.

The laminar-turbulent transition in hypersonic flow on a blunt hemisphere is studied with Navier-Stokes and parabolized stability equations. Maximum transient kinetic energy growth is found close to the sonic point, which could explain the transition observed in wind tunnel and flight experiments.

The convective-absolute nature of icicle ripples and ice ripples is addressed through the use of the cusp map method. The evaluation of the absolute wave number suggests a novel interpretation of some recent experiments.

The electrostatic stabilization of thin viscous films, including the effect of the solid regions bounding the liquid-air system, is presented. The derived asymptotic theory is compared with direct numerical simulations and active control mechanisms, such as mixing applications, are proposed.

Feature-resolved multiphase simulation and theory explore drag-reducing ingredients of superhydrophobic surfaces. A nonmonotonic relation between interface contact angle and drag reduction is observed. An expression is derived for effective slip length that accounts for liquid penetration.

A wavelet-based filtering method is presented that extracts clusters of inertial particles in turbulent flows and also enables grid adaptation resulting in nonuniform meshes refined around the particle clusters.

In numerical simulations, gas-solid flows of cohesive particles in fluidized beds and riser flows show reverse dependence on particle friction and restitution coefficient. The reverse sensitivity is due to switching of dominant particle interactions from enduring contacts to binary collisions with decreasing solid concentration.

The mixing of passive tracers in unsteady fluid flow is considered. A general systematic framework is proposed to determine the optimal initial condition of the passive tracer so that the most homogeneous mixture is obtained after finite-time advection.

Fluid particles trajectories are reconstructed experimentally and numerically in a high Reynolds number turbulent channel flow. A statistical Lagrangian analysis of acceleration and velocity reveals a complex behavior and a persistent anisotropy at the smallest scales.

A prediction (solid line) for the ultimate-state transition Rayleigh-number, with its pre-factor adjusted to fit the experimental value for a Prandtl number Pr = 0.82, passes through the DNS estimate for Pr = 0.021. Cryogenic observations of transitions (solid circles) fall well below this line.

An artificial neural network establishes a turbulence model for large-eddy simulation using direct numerical simulation of a turbulent channel flow. The resulting model is similar to an existing turbulence model (the gradient model).

An analysis of the triadic interactions of helical modes in magnetohydrodynamic turbulent flows gives further understanding of fundamental aspects of the interscale dynamics of magnetic helicity, in particular, concerning the bidirectional nature if its turbulent cascade.

A theoretical and experimental investigation validates that the Kolmogorov first similarity hypothesis ($\nu$ and $ϵ$ are the relevant controlling parameters for small-scale turbulence at high Reynolds number) is subsumed under the more general hypothesis of self-preservation of the Navier-Stokes equations.

Enstrophy-like conservation is found in a subset (G2 R-class) of helical interactions, causing the energy cascade to reverse.

Multicomponent turbulence measurements in rough-wall boundary layers are presented and compared to smooth-wall data over a large friction Reynolds number range. The results are discussed relative to the combined influences of roughness and Reynolds number on the scaling behavior of boundary layers.