An inertial swimmer comprised of two unequal spheres oscillating in antiphase generates a steady streaming, which propels the swimmer in opposite directions depending on the Reynolds number.

Numerical solutions of the compressible Navier-Stokes equation for a bubble collapsing close to a solid boundary find a very thin jet with velocities of 1000m/s.

High speed observations are made of the pinching off of a pendant drop.

In experiments a surface acoustic wave at 20 Mhz propagating down a vertical surface induces a liquid film to climb up the surface against gravity.

Using 3D averages of energy dissipation rather than a surrogate quantity, high-resolution volumetric measurements and numerical simulations show that velocity increments scale with the local dissipation rate as per Kolmogorov’s 1962 refined similarity hypothesis, supporting small-scale universality.

Three-dimensional numerical simulations of forced turbulence in a thin layer show the transfer from the forcing to larger scales is by two-dimensional modes, and to smaller scales by three-dimensional modes, the latter providing a viscosity-independent dissipation.

A genetic algorithm is used to optimally populate a random flow with two-dimensional Gaussian-shaped vortices subject to certain constraints.

We study inertial spherical squirmers prescribing tangential surface deformations. Breaking axial symmetry induces rotation-translation coupling that overcomes the “scallop theorem”, giving net motion for time-reversible strokes. This swimming mechanism may be relevant for large Volvox colonies.

The utility of particle tracking velocimetry for characterizing the quantized vortex tangle in He II thermal counterflow is shown by demonstrating measurements of vortex line spacing, the parameter $c_2$, and vortex reconnection.

Experiments show that the separation between two spheres settling down in viscoelastic shear-thinning solutions exhibit two different regimes depending on the fluids’ rheological properties. The existence of a previously reported elusive regime is corroborated.

Experiments in turbulent rotating Rayleigh-Bénard convection find various statistical properties of the fluctuations of the temperature which can be fit with a model.

RT instability and convection in confined porous media is examined via DNS. Interactions between gravity and diffusion produce efficient fluid mixing, and a superlinear asymptotic growth of the mixing rate is observed and modeled for the first time. Potential geophysical applications are envisioned.

Long gas bubbles in a vertical tube do not rise in stagnant liquid if Bo < 0.842; but what happens if a net liquid flow rate exists? We show that long bubbles rising in co-current liquid flow exhibit different asymptotic regimes at small liquid capillary numbers, as Bo transitions across this critical value.

Formation of a liquid jet and drop as a consequence of the bursting of a bubble in symmetric and asymmetric neighborhoods is modeled numerically. We find that unbalanced interaction of neighbors forces the jet and drop to bend towards the absent bubbles.

Multimodal stability analysis and parabolization are combined to account for dominant mode interactions in pretransitional flow. A sequence of linear progressions of the resulting parabolized Floquet equations captures disturbance growth and provides excellent agreement with direct numerical simulation results.

We use the self-organizing map, an unsupervised machine learning method, to find the turbulent/nonturbulent interface in a transitional boundary layer with the help of Johns Hopkins Turbulence Databases. This method separates turbulent regions from vortical streaks and free-stream turbulence.

The motion of wall-bounded drops moving on solid substrates driven by a fully turbulent channel flow is experimentally investigated. A scaling is found to describe the dimensionless drop velocity in terms of a dimensionless flow attack velocity, taking into account the surface wetting properties.

We observe silicone oils wicking across dendritic sheets of frost. The capillary action is found to be dependent upon both the surface orientation and the underlying surface wettability.

Experiments on the low-Reynolds number settling of a sphere through a fluid interface focus on the effect of the viscosity ratio and Bond number on the shape of the sphere position curve as a function of time, whether sinking occurs through a tailing or film drainage mode and the sinking timescale.

The application of the deterministic lateral displacement approach in microfluidics to deformability-based sorting of cells is explored. Mesoscale hydrodynamics simulations are employed to show that this requires large flow-induced cell deformation in the trajectory-distinguishing flow region.

The compressible Navier-Stokes equations already include the self-diffusion effect. Comparisons with 35 experiments show that the self-diffusion effect is too small to account for the mass flow rate enhancement in steady compressible gas flow through a microconduit in the slip flow regime.

Long droplets entering a microfluidic T-junction get trapped below, and break beyond, a critical capillary number, which is determined theoretically and experimentally in this work.

A simulation study of a dense granular inclined plane flow reveals a sharp transition between a Bagnold flow and a layered flow at critical angle, which is a fraction of a degree above the cessation angle. The layered flow exhibits intriguing features, such as oscillations of the flow velocity.

Finite-size Lagrangian coherent structures can arise in dilute suspensions solely because of the size of the particles. When moving near boundaries, a lubrication-induced drag transfers the particles from the chaotic sea of the unperturbed fluid flow to particular Kolmogorov-Arnold-Moser tori.

Many large spherical particles that sediment and resuspend from the bottom of a duct under fully developed turbulent conditions are studied. Optical experiments and direct numerical simulations are compared and used to investigate turbulence modulation and organization of particles.

Agglomeration of adhesive particles in turbulence is investigated. The size distribution of early-stage agglomerates follows a unified exponential scaling. A new agglomeration kernel containing information about the fractal structure of agglomerates and the sticking probability is constructed.

Lessons learned from the motion of red cells in capillaries are applied to a novel experimental study of soft porous lubrication, which conclusively demonstrates a dramatic decrease of friction coefficient with tremendously enhanced pore pressure as a planar board glides over a soft porous layer.

A new hydrodynamic instability in driven active matter is discussed. It is similar to the convective instability that occurs in passive fluids, but differs in several important ways. In particular, the transition to turbulence in the active matter system is expected to be novel.

Pouring a liquid down into a container of a denser liquid creates a fountain. We measure the penetration depth of such fountains and characterize the mixing based on the Reynolds (Re) and Froude (Fr) numbers.

The importance of zonal modes in discussing three-wave resonant nonlinear interactions in two-dimensional turbulence on a rotating sphere is investigated. Zonal modes should not be ignored although the energy exchanges between zonal and nonzonal modes by resonant interactions are not possible.

High-fidelity simulations show that the confining effect of sidewalls on a shock-wave/boundary-layer interaction can have a very strong influence on both the mean flow and large-scale unsteadiness, and accurately capturing the sidewall flows is essential in realistic modeling of confined flows.

Using a recent alternative form of the 4/3 exact relation for fully developed hydrodynamic turbulence, the incompressible energy cascade rate $\epsilon$ is computed. The numerical results show that $\epsilon$ is in clear agreement with the cascade rates computed from the classical 4/3 law.

Large-eddy simulations show the similarity of turbine wakes for different tip speed ratios and suggest the coexistence of inflow large eddies and wake shear layer instability as the mechanism for the onset of wake meandering.

From the linear equation for the velocity defect in the outer boundary layer, the product of mean wall normal velocity and free stream velocity is shown to vary linearly with the Reynolds shear stress.

We study the total scalar variance equation for fully developed turbulent channel flow subject to uniform scalar generation. We find a total scalar variance leading balance four-layer structure similar to total kinetic energy balance. Differences in the two Karman constants, k and k_θ, are clarified.

Analytical considerations, based on the Navier-Stokes equations, which take into account the finite Reynolds number effect, together with all available experimental laboratory data, confirm a tendency towards the universal predictions of K41 as the Reynolds number continues to increase.

It is shown that decaying helical turbulence amplifies a weak magnetic field, which then itself becomes helical. However, it displays a transient behavior different from any other helical or nonhelical magnetic decaying field in a parametric representation between the temporal scaling exponents $p(t)$ and $q(t)$.

Homogeneous rotating turbulence structure is investigated by analyzing instantaneous statistics of the scale-dependent perceived velocity gradient tensor. Rotation is shown to suppress some alignment properties of isotropic turbulence, decreasing enstrophy production and strain production rates.

We experimentally compare wakes within three-bladed rotor and porous disk wind turbine arrays using PIV measurements and proper orthogonal decomposition. Disparities between rotors and disks with important implications for wind turbine simulations is found.

A certain homogeneous fully developed turbulence, which was initially reflection asymmetric at large scales, is studied theoretically and numerically. It is shown that the turbulence does not relax to any reflection symmetric state, even in the energy containing range.

Reconnection of vortex tubes containing twisted vortex lines is studied by numerical simulation, showing that both the sense and strength of the twist affect the topological and geometrical properties of the resulting vortex structures, as well as the timing and rate of the reconnection process.

Impulse-based vortex formulas are found appropriate for computing propulsion forces from experiments only when the vortices remain close to the moving foil, as in starting motions or in hovering flight, but are inaccurate in forward flight or swimming, where projection methods perform much better.