An experimental study of chaotic mixing in viscoplastic fluids using stirring rods in a rotating vessel finds that the mixing is limited at a given time to the zone localized around the stirring rods that has high shear.

While chemically-active homogeneous spherical particles do not undergo self-diffusiophoresis in free solution, they may do so when suspended in the vicinity of a solid boundary.

A bubble interacting with an inclined wall may either slide steadily or bounce on it repeatedly. This experimental study, conducted using several fluids and bubble sizes, explains the transition and gives a criteria for this change of behavior.

By vibrating a rib, two Fourier modes are injected into a turbulent boundary layer. Modes with sum, difference, and double the frequencies are detected downstream, and their amplitudes across the boundary layer are investigated.

Koopman modes and resolvent modes are related via system symmetries, with continuous spatial symmetry inducing a decomposition into travelling waves. The resolvent modes are the optimal approximation to the mapping from the Koopman modes of the Reynolds stress divergence to the velocity field.

Highly confined capsules—most notably red blood cells—are observed to flow in a seemingly stable train. However, with less confinement this striking order is disrupted, and the train breaks apart into an apparently chaotic flow. Non-modal stability analysis of a model capsule train illuminates the mechanisms of the break-up.

Flying is a delicate balance of lift versus weight and thrust versus drag. But the flapping wings of animals do not seem to abide by the aerodynamic laws of airplane wings. A new study shows that fast wing oscillations – like that used by flying insects – lead to fundamental changes in the physics of drag or wind resistance. The steady motion of airplane wings leads to a resistance that increases as the square of speed. The new research shows that flapping wings instead have a drag that increases in direct proportion to their speed through air. This means that, to go twice as fast, an airplane must generate four times the thrust, while an insect only needs to produce twice the thrust.

Careful selection of a Mach number in a shock tube can produce a standing reflected shock wave. Its perturbed density/pressure discontinuities vary with time but otherwise are fixed in space, greatly facilitating their measurement.

A new analysis of dissipative effects in plane Couette flow near a soft solid boundary

A homogeneous and stationary random process is used to describe scattering of near-inertial-waves by a geostrophic flow. The authors focus their studies on waves whose phase varies on the same horizontal scale as that of the geostrophic flow and demonstrate that scattering redistributes energy only between waves of equal wavenumbers, corresponding to equal-frequency waves in the shallow-water system.

As a disk moves through an oil-water interface, it entrains part of the oil into the water phase through a funnel-shaped volume. New experiments show that the shape of this volume is determined by a combination of potential flow and a starting vortex, but surprisingly, its shape remains independent of the disk velocity.

Electric–field induced deformation and relaxation of a prolate low–conductivity drop. At time $t=t_{\text{initial}}$, a spherical drop is placed under a uniform DC electric field given by ${\mathit{E}}_{\mathrm{\infty }}$, directed from left to right. The drop attains a steady–state three–lobed configuration at $t=t_{\text{deform}}$. Upon removal of the applied field, the drop achieves breakup at $t=t_{\text{relax}}$ via an end–pinching mechanism.

When slightly bent, an elastic filament at a viscous interface straightens due to bending torques, but when greatly deformed, a nonlinear tensile force along the filament becomes equally important, and causes much faster relaxation. Asymmetries about the center relax even faster.

Pairs of droplets are brought together with constant force and made to coalesce using a cantilevered capillary setup. Time scales for coalescence are measured and compared with existing scaling theories. No model shows complete agreement with experiments, but one predicts the correct dependence on droplet radius.

Inspired by the fur of semi-aquatic mammals, this hybrid experimental and theoretical study investigates dynamic air entrainment in hairy textures. Using a porous media model, the air entrainment is described via a competition between the hydrostatic forcing and the viscous resistance in the pores.

Extending the experimental study of diffusiophoresis to the large scale shows that its presence influences the global mixing performance at all the scales in the global system, ranging from nanoscale up to centimeter scale.

Expressions for the ratio of the turbulent Schmidt to Prandtl numbers are derived for atmospheric flows over water surfaces. A unity value is consistent with the active role of temperature in turbulence generation even when perfect correlation between turbulent temperature and water vapor fluctuations is absent.

In an experimental investigation of plane Couette flow under spanwise, anticyclonic system rotation, analysis of the Reynolds stress transport equation shows that there is a transport of the Reynolds shear stress towards the center of the channel, which may then result in a negative mean velocity gradient there.

The enstrophy inertial range dynamics of generalized two-dimensional turbulence is investigated using the Eddy-Damped Quasi-Normal Markovianized approximation equation. The transition to $k^{-1}$ spectrum is analytically derived and the non-local triad interactions are shown to be responsible for the transition.

Experiments show that when two submerged jets are pulsed together, vortex formation is perturbed and the total thrust generated by the jet pair is reduced. A physical model of the interaction reveals strategies to control the vortex dynamics and mitigate performance loss in multi-jet systems.