Researchers experimentally characterize the response of helically swimming alga to oscillatory shear flows and find that algal swimming trajectories orient perpendicular to the flow-shear plane. Their results have implications for both active suspension rheology and the design of novel cell processing methods.

A scaling law is found for the drop on the top of the jet that arises when a bubble bursts.

Experiments on leidenfrost dynamics of water deposited in conical bowls reveal a maximum evaporation time for a given angle of confinement. The drop profile is numerically computed and the different observed regimes are explained as a result of two mechanisms of vapor release: chimneys, suppressed when confinement increases, and lateral flow along the walls.

The effective slip length for flow over a mattress of bubbles is considered in the singular limit of close separation of the bubbles. The slip length is shown to diverge inversely with the square root of the solid fraction and three terms in an asymptotic expansion are determined.

The dynamics of small buoyant particles in stratified turbulence is numerically investigated as a model for the formation of thin phytoplankton layers in the ocean.

Starting from one value of the Reynolds stress, the variability of its evolution is measured in different mean flows by ensembles of 5000 simulations of 20,000 Fourier modes.

Liquid plugs may damage the airways of mechanically ventilated patients, leading to ventilator-induced lung injury. Plugs reduce gas exchange and injure tissues through mechanical stresses. A new model estimates the motion and stresses of plugs and may be useful for large-scale simulations of the diseased lung.

Experimental and numerical methods are combined to analyze the flow field around the nematode $C.$ $elegans$. Planar PTV flow data can underestimate 3D shear rates by 40%, but this may be corrected via a simple formula.

A suspension of magnetotactic bacteria is driven against a Poiseuille flow in a magneto-microfluidic experiment. Fine tuning of the control parameters allows a transition from a single-cell regime, well described by analytical results, to a spectacular artificial bioconvection phenomena.

The dynamics of single polymers in large-amplitude oscillatory extensional flow are studied over a wide range of flow strengths and cycle frequencies using a combination of single-molecule experiments and Brownian dynamics simulations.

Stratified flow between co-rotating vertical cylinders has many similarities with the dynamics observed in stellar and planetary accretion disks: The flow has rotation, anticyclonic shear, and a stabilizing density gradient parallel to the rotation axis. A new experiment extends the scope of previous work and demonstrates inconsistencies with linear instability theory, both viscous and inviscid.

An investigation of the linear stability properties of a boundary layer flow around a semi-infinite rotating cylinder reveals that the stability characteristics significantly depend on the rotation rate.

Complex interrelated mechanisms mediate the stability of hypersonic boundary layers. Simulations are used to investigate key mechanisms of primary and secondary instabilities, including nonparallel effects and intermode phase synchronization.

A computational study of the flow past freely deforming bubbles rising in still liquids is reported, refining the critical curve associated with path instability. Depending on the relative strength of inertia, viscous, and capillary effects, different regimes are observed in which the characteristics of the path, bubble shape, and wake structure, together with their couplings, are examined in detail.

A new study shows that a moving contact line could be more dangerous for a hydrophobic coating layer on a surface than lamellar flow. The tiny water drops generate a driving force that removes the coating molecules, collecting and depositing them on the substrate as the contact line recedes.

The roughness of a solid is known to increase the minimal temperature for observing the Leidenfrost effect. A new study shows that a volatile liquid drop placed on the surface of a smooth substrate—a non-volatile liquid pool—reaches the Leidenfrost state as soon as the liquid of the pool is just hotter than the drop boiling point, with no apparent Leidenfrost threshold.

A bumpy bubble mattress maximizes fluid flow over it. A team of theorists explain this phenomenon by looking at the viscous dissipation distribution. For an increasing protrusion angle, dissipation decreases near the bubble corners, while it increases in the bulk. These two antagonistic effects lead to an optimum protrusion angle.

An experimental study of the flow of superfluid helium through single nanopipes with radii of order 100 nm and lengths of a few millimeters, reveals the existence of two distinct flow regimes above and below a critical pressure drop $P_c$. For $P>P_c$, the flow velocity is more than an order of magnitude higher than the Feynman critical velocity.

In a nearly frictionless channels such as narrow carbon nanotubes, flow is limited by the viscous dissipation occurring at the tube mouth. Using both numerical and analytical approaches, it is demonstrated that such end effects can be reduced to a considerable extent by adding an entrance of well-chosen shape.

Scientists perform direct numerical calculations aimed at the optimization of drug delivery agents such as targeted therapeutic nanocarriers. The emphasis of their work is on hydrodynamic interactions between the nanocarrier and the vessel wall mediated by the fluid flow, and how the hydrodynamic interaction varies as the particle transitions from being at the center of the vessel to being very close to the wall prior to binding.

A theoretical and numerical study on the motion of isotropic helicoids is presented. It is shown that heavy isotropic helicoids preferentially sample different helical regions in laminar or chaotic advecting flows.

New results on the computation of shock interactions with a 3D array of spherical particles, fixed in a face-centered-cubic arrangement, quantify multiparticle effects on their drag for different volume fractions and strengths.

Thermal plumes are prominent coherent structures in convective turbulence and are responsible for heat transport and initialization of the “wind” of turbulent convection. It is difficult to experimentally measure their properties spatially, but researchers have developed a method to characterize the plumes and their contributions to thermal fluctuation using temporally measured temperature signals in turbulent Rayleigh-Bénard convection.

Recent experimental work reported the first evidence that time-reversal refocusing of waves can be applied to water waves. Now the first numerical study related to the validation of time-reversal applicability to hydrodynamics, beyond laboratory limitations is presented.

The effects of anticyclonic rotation on turbulent statistics and flow structures are studied through 20 direct numerical simulations, covering many qualitatively different flow regimes, from rotation numbers $Ro=0$ to $Ro=0.9$.

High-resolution direct numerical simulations of turbulent Taylor-Couette flow in large periodic domains reveal that the large-scale rollers that are formed are very nearly fixed in space and their axial wavelength may sensitively depend upon the initial conditions.

The cascades and spectra in the elastic range of 2D Cahn-Hilliard-Navier-Stokes turbulence are investigated by DNS. Puzzling results for the mean-square concentration and kinetic-energy spectra are reconciled by observing that “elasticity” is limited to the interface layers between concentration blobs. Thus the packing fraction of interblob interfaces emerges as critical to the physics of turbulence in a spinodal decomposition.

Intense recurring bursts of turbulence triggered by a linear instability are seen in several rotating channel flow simulations even when the flow is partly strongly turbulent. Linear stability analysis agrees in some cases with simulations, but in others the growth rate is over-predicted.

High-resolution numerical simulations show that rotation decreases the production of turbulent velocity fluctuations in Rayleigh-Taylor turbulence thus decreasing the growth of the turbulent mixing layer. Rotation also reduces the turbulent heat transfer and leads to a different regime in the Nusselt-Rayleigh scaling.

An inner-outer interaction model for predicting statistics of the near-wall streamwise velocity fluctuations via an input signal in the log region is refined using linear spectral stochastic estimation. Velocity fluctuations that are stochastically coherent between the outer and inner region are processed with a scale-dependent gain and phase during predictions.

As the strength of an external uniform magnetic field is increased in a 3D magnetohydrodynamic flow, the flow can undergo a transition and change its dimensionality. Numerical simulations using helical mechanical forcing show that the presence of helicity changes the spectral scaling of the energy and affects the statistics of velocity field fluctuations. Morever, for very strong external magnetic fields a direct cascade of mechanical helicity is observed, which allows derivation of scaling laws for the system.

The circulation of streamwise vortices generated by a hypermixer strut in a supersonic flow is studied theoretically and numerically.