The star-nosed mole sniffs for prey underwater by rapidly blowing a bubble, then sucking it back in before the bubble detaches from the nose. Experiments show how the bizarre shape of the mole’s nose might contribute to stabilizing bubbles during the sniff, enabling this behavior.

Suspensions of bioluminiscent bacteria display convective motions reminiscent of classical bioconvection, but this poses a conundrum, as these organisms lack flagella-driven motility under the conditions studied. Instead, evaporation of the salty growth medium is found to drive the convection.

Two-dimensional simulations are conducted to assess the effects of disturbance on detonation initiation. A disturbance can induce a complex shock wave interaction which induces a local explosion. Disturbances can thus be used to promote detonation initiation.

Swimmers comprised of two rigid spheres that oscillate periodically along their axis of symmetry are examined. In viscoelastic fluids, the swimmers propel in the direction of the smaller sphere when the two spheres are of different sizes.

The slip behavior observed experimentally between close spheres is described by an analytical model in terms of the apparent shear-thinning rheology of the solvent. The results compare well with experiments and bridge the hidden solvent shear-thinning theory for suspensions with slip-based models.

Enabled by a newly developed species perturbation parameter, an analysis identifies forebody surface chemistry, among all other competing thermophysical processes, as the key contributor to continuum breakdown in hypersonic reacting wake flows.

A new convective model in rotating spherical shells, with a temperature-dependent internal heat source, is studied by means of three-dimensional simulations. The potential applicability of the results to the evolution of thermonuclear bursts in accreting neutron star oceans is explored.

The lateral migration of a vesicle (a model of red blood cells) in a bounded shear flow is investigated numerically. It is found that there exists an off-center stable steady state of the vesicle in addition to the usual centerline, depending on the initial position and viscosity contrast.

Velocity fields determined within and surrounding a drop moving through an orifice reveal the relative importance of local deformation, fluid rotation, and dissipation in the surrounding fluid as well as the coupling between fluid inertia and contact-line motion.

The evolution of the shape (but not the position) of a long bubble or droplet in a self-rewetting system in a nonuniformly heated tube is shown to be driven entirely by Marangoni effects: a wide droplet widens (and ultimately fills the cross section of the tube), whereas a narrow droplet narrows.

The dynamic behavior of two neighboring nanobubbles is investigated for various gas-liquid-solid interactions. Two neighboring unsaturated surface nanobubbles can form a gas-rich layer on a solid surface, as long as the interaction between the solid and the gas is sufficiently strong.

Side view of the full rotation of a two-phase giant vesicle doing a tanktreading motion under a shear rate of 5 $s^{-1}$. The major axis of the vesicle oscillates showing the vesicle swings similarly to a red blood cell.

As a first step towards the description of magnetohydrodynamic (MHD) dispersed two-phase flows, a permanent MHD channel flow past a stationary sphere is numerically investigated, highlighting the gradual emergence of atypical MHD flow patterns, among them a genuine “ghost column.”

A parametric study of dynamos in a rotating sphere shows a rich space of dynamic solutions, with stationary, aperiodic, and small-scale dynamo regimes controlled by Ekman and Reynolds numbers. Magnetic reversals are observed, displaying $1/f$ noise and statistics reminiscent of geodynamo observations.

Two-dimensional numerical simulations of high Rayleigh number convection in a porous medium explore the effect of increasing anisotropy of mechanical dispersion on the convective pattern and flux.

The effect of one obstacle on the drag on a second obstacle is measured for square obstacles in subcritical open channel flow. The lowest drag occurs when one obstacle is shielded directly behind another, and the largest drag occurs on a slightly upstream obstacle in near side-by-side arrangements.

We numerically investigate temporal aspects of turbulent spot spreading in plane Couette flow for transitional Reynolds numbers, focusing on streamwise spreading. From the topology of turbulent spots and associated large-scale flows, we propose a decomposition of the streamwise growth rate.

The Self-Sustaining Process (SSP) proposed in the 1990s by Waleffe is a widely-accepted building block of transition to turbulence in shear flows such as plane Couette flow. Although inspired by the rolls and waves of Taylor-Couette flow, the SSP had not been investigated for this flow until now.

The three-dimensional flow generated below a liquid-vapor meniscus during low-pressure water evaporation is quantified with experiments using scanning particle image velocimetry and compared with an extensive numerical model. Results show how buoyancy effects in the liquid may suppress thermocapillary flows at the interface.

The flow within microscopic indentations filled with a lubricant fluid is studied by varying viscosity ratio, surface tension, and lubricant-to-working-fluid volume fraction. This yields protrusion heights that readily quantify the drag reduction of a lubricant-impregnated microstructured surface.

Experiments show that small spheres can pass through an oil-water interface and be coated with a predictable oil film when the Bond number is between 1.5 and 7.5. The film thickness is approximately proportional to the Bond number, which makes it a convenient method to coat particles with a designed film thickness.

Weakly nonlinear analysis is used to study fingering instabilities in radially tapered (converging and diverging) Hele-Shaw cells. It is found that changes in the capillary number modify the interface instability behavior and the finger shapes relative to what usually occurs in parallel-plate cells.

Deterministic lateral displacement (DLD) is used to sort red blood cells (RBCs) by their mechanical properties. This enables rapid medical diagnosis of diseases such as malaria. A systematic way of discovering new DLD designs for efficient sorting of RBCs with similar mechanical properties is proposed.

The relaxation of a liquid drop in a Hele-Shaw cell is observed experimentally and then modeled successfully.

A theoretical study of rigid helices sedimenting under gravity finds they either follow a helical path downwards, or exhibit complicated oscillations close to the horizontal orientation.

Experiments on unsteady granular avalanches, which are uniform in the flow direction, allow for observations of the evolution of the flow depth, the velocity profile, and the concentration distribution. A simple, physically-based, analytic model is proposed to fit the observations.

Combining new and old data, we find that particle settling speeds are well-described by the empirical Richardson-Zaki function up to jamming, but surprisingly, there are separate branches for Brownian and non-Brownian particles with a crossover at an extraordinarily large Peclet number of ${10}^8$.

Standing wave patterns can occur both in vibrated granular layers and pulsed fluidized beds. Although the different type of excitation results in a different definition of the driving parameters and instability curve, a theoretical study shows that the instability criterion in both systems is similar.

An equation of motion is derived for isolated bubbles in turbulence, an equation similar to that governing phytoplankton. Simulations show the clustering of bubbles in vertical columns.

Laboratory experiments on the evolution of a sediment bed under a spin-down flow show the emergence of diverse types of patterns. The net radially inward sediment transport is quantified and explained through an analytical derivation of the total radial force exerted on the bed.

We show that local structure, in an otherwise random medium, can change the nature of invasion percolation phenomena, including multiphase fluid flows. By combining microfluidic drying experiments with simple models we explain how local correlations in pore sizes lead to more extreme dynamics.

Transient dynamics of a Leidenfrost vapor layer in drop impact is studied using x-ray imaging. It is shown that a vapor disk first forms, growing in thickness, following Fourier’s law. At a certain thickness, ripples generate near the edge and propagate to the center by capillary waves, improving evaporation.

Neutrally buoyant finite-size particles laden in stratified turbulent channel flows are found to enhance internal gravity waves, thus blocking heat transfer. In the near-wall region, these particles are preferentially located in the high-speed streaks.

It is known that turbulent energy is rapidly transferred in the direction of the rotation axis in a rotating system, in comparison with the nonrotating case. A new turbulence model of the energy flux predicting this phenomenon is proposed and discussed in terms of turbulent helicity.

In two-dimensional turbulence, we show how to create devices able to feed on the turbulent fluid motion by coupling with underlying features of the energy cascade. By changing the shape of the device, we can turn it into a self-propelled vehicle or a rotor powered by turbulence.

This paper presents wind tunnel data for 56 different layouts of a scaled wind farm with 100 porous disk models. The data indicates that a nonuniform streamwise spacing between turbine rows can increase power output in the fully developed and entrance regions of large wind farms.

Direct numerical simulations show that for dual-plane jet flows with different separation lengths, the streamwise evolutions of various statistics along the centerline all scale with the proposed jet-interaction length scale. The spatial evolution of the $-5/3$ scaling law is closely related to the non-Gaussian velocity fluctuations.

Adopting Lie symmetry group theory both Kolmogorov and non-Kolmogorov scaling and dissipation laws are explored theoretically for a turbulent planar jet. We find that the jet entrainment coefficient varies with streamwise distance when non-Kolmogorov scaling laws hold.

Both the spanwise and the vertical velocity components in high-Reynolds-number wall-bounded flows may be modeled via a random additive process. Evidence shows that a hierarchical, treelike structure exists for the spanwise velocity component.

Our numerical simulation finds that flattened three dimensional turbulence generates strong intermittency at the crossover scale between two and three dimensions. This provides a mechanism for disaster causing extreme events below the synoptic scale in the atmosphere such as tropical cyclones.

We study buoyancy-driven variable-density homogeneous turbulence with a two-point spectral closure model and assess model accuracy relative to direct numerical simulations using standard metrics. The model captures statistics of spectral distributions and global means at low and high Atwood numbers.

An analysis shows that on the centerline of a planar wake, turbulent dissipation obeys the nonequilibrium scaling, provided that the large-scale contribution of the coherent motions is disregarded. In that same region, the dissipations associated with coherent and incoherent motions vary together.

Can you gain “insight” by relinquishing some of your sight? Indeed, we show how to quantify the energy content of various structures in a flow by observing it through “eyeglasses” of varying strength. We also introduce a new class of “lenses” with a simple design which yield more accurate results.

This works shows for the first time that an inexpensive ensemble of low-order vortex models can accurately capture the aerodynamics of a low Reynolds number separated flow, even when disturbed by gusts, when it assimilates measured surface pressures.

A novel breakdown mechanism is observed during the head-on collision of two vortex rings. The interacting cores locally flatten into extremely thin vortex sheets and split into smaller daughter filaments iteratively over two generations, leading to the rapid emergence of fine-scale vortices.

Rogue waves in the interior of a stratified fluid are modeled as special breathers (pulsating modes) arising from long-wave–short-wave resonance. Features like the existence condition and waveforms contrast sharply with those of free surface waves governed by the nonlinear Schrödinger equation.

A new amplitude equation that captures the effect of arbitrary topography on surface waves is presented. It can be integrated more quickly than the fully nonlinear equations, while accurately capturing the wave dynamics.

An envelope equation to model the propagation of surface waves in deep viscous fluids is proposed. The dispersion relation comprising viscosity and surface tension is expressed as an operator and used to generalize the universal nonlinear Schrödinger equation and quantify nonlinear damping.

We conduct experiments on Faraday wave patterns and bouncing droplets with a high-density/surface tension liquid metal fluid. Bouncing liquid metal droplets can be sustained on the wavy surface, self-assembling into various lattice structures which can be switched with an electric field.