The width of the spectrum of the velocities is observed in inertial wave rotating turbulence to be linearly related (at small widths) to $Uk$sin($\theta$), indicating nonlinear interactions with the mean flow are the main cause of the broadening of the spectrum.

Bacteria swim in viscous fluids by rotating helical flagellar filaments which dynamically bundle around each other. We derive and study a bundling model whereby straight rotating elastic filaments in viscous fluid induce rotational flows which tend to bend and wrap the filaments around each other.

Swimming microorganisms commonly encounter anisotropic environments, such as a biofilm or a liquid-crystalline solution. A simple theory for a Taylor sheet in a nematic liquid crystal is used to calculate how the swimming speed depends on the angle between the swimmer and the nematic director and also on the torque that tends to align the swimmer with the director.

Experimental study on discontinuous shear thickening fluids reveals that the relaxation times agree with a generalized Newtonian model for lower weight fractions. At high weight fractions, however, the relaxation times disagree by up to 4 orders of magnitude.

Outflow of granular material from containers with small orifices is a ubiquitous phenomenon. A study using hydrogel spheres as templates of soft particles shows that the softness of the grains has considerable consequences: it changes the macroscopic dynamics qualitatively.

The effectiveness of a widely used phenomenological approach for modeling vibrational excitation is evaluated by comparison with a higher fidelity approach based on an $ab$ $initio$ computational chemistry analysis. A parameter is formulated to predict when the phenomenological approach is inaccurate.

Under rarefied conditions, gas flow can be induced by nonuniform temperatures on bounded walls. Thermally induced flow in an enclosure with nonisothermal walls is analyzed by directly solving the gas kinetic equation via a discrete velocity method with a memory-reduction technique.

Characteristic properties of turbulent Rayleigh-Bénard convection in the bulk and the boundary layers are summarized for a wide range of Rayleigh and Prandtl numbers, with a specific emphasis on low-Prandtl-number convection.

Upper bounds E for the poloidal kinetic energy in thermal convection are derived from known bounds on the Nusselt number, and are improved by solving a separate optimization problem. The same procedure leads to a bound on the dissipation due to non poloidal velocity components.

Superhydrophobic surfaces are designated by a low wettability that gives rise to self-cleaning. This study analyses the fluid dynamics of self-propelled droplet jumping upon binary unequal sized droplet coalescence with three-dimensional simulations.

Droplet breakup in a microfluidic T junction is studied experimentally and numerically (3D) inside continuous phases made of shear-thinning solutions. In squeezing and dripping, the droplet length is found to scale with an effective capillary number, accounting for shear dependent viscosity.

Acoustic streaming designates the ability to drive flows by acoustic propagation in dissipative fluids. We present an experimental study of a square flow driven by acoustic streaming. The flow evolution from steady to strongly unsteady is characterized, and a transition is observed between two regimes.

A turbulent wake retains a memory of upstream disturbances which fades over a longer distance for lower viscosity. For a zero-viscosity superfluid, numerical simulations find a subtle memory effect that explains a number of contradictory experimental observations.

Inspired by the axial grooves of the Saguaro cactus, active aerodynamic drag on morphable cylinders, whose topography can be tuned pneumatically, is studied. The active samples are controlled, on demand, to obtain drag coefficients that are significantly lower than for samples with fixed morphologies.

Drag reduction capability of uniform blowing in supersonic turbulent boundary layers is investigated by means of direct numerical simulation of channel flows with uniform blowing on one side and suction on the other side under subsonic and supersonic conditions.

An analysis of the conditions under which air bubbles may be trapped during the coating of microstructured substrates reveals, among other intriguing observations, that superhydrophobic flow patterns can arise even when the substrate is hydrophilic.

Based on experimental and numerical data from a wide range of flow conditions, relations linking the film-thickness statistics to the bulk-velocity statistics of wavy falling-film flows are developed from a Reynolds decomposition of the local time-varying film thickness and bulk velocity.

Most rotating Hele-Shaw cell studies assume a constant cell angular velocity and neglect inertial effects. This work considers a time-dependent angular velocity and includes inertia. These two new elements introduce important changes in the linear and weakly nonlinear dynamics of the problem.

We propose that strategic use of an array of periodic patterns on a debonding contactor during elastic contact lithography can transform a flat polymer surface into a biomimetic super-hydrophobic surface having high-aspect ratio hierarchical patterns with tuneable adhesive properties.

Gas diffusion rates in and out of superhydrophobic surfaces in transitional and turbulent boundary layers are observed and measured at varying Reynolds numbers, pressures, and dissolved gas concentrations. Results show a power-law correlation between the Sherwood and friction Reynolds number.

Focused on evaporation-induced contact angles, asymptotic analyses in the limits of weak and strong Kelvin effects in the framework of Wayner’s and de Gennes’ paradigms permit a unified treatment and systematization of various isolated cases encountered in the literature.

Stokes flow is generated by repeatedly oscillating a pair of rigid rods. Table-top experiments and simulations reveal that a simple phase delay gives rise to complex flow patterns.

Experiments on flows through rectangular microchannels with a small amplitude sinusoidal profile on one wall confirm the existence of three regimes of perturbations that depend on the ratio of channel depth to roughness wavelength, $\alpha$, and the dimensionless viscous length, $\theta$, in agreement with theory.

Fluid flow through porous media is determined by the underlying pore structure. An analytical relationship is proposed between the distribution of the width of small openings and the distribution of low fluid velocities in the medium, which control the statistics of fluid transport and mixing.

We find expressions for the change in hydrodynamic slip length when a weakly shear-thinning fluid flows longitudinally, or transversely, over a periodic array of flat, unidirectional no-shear slots from a modified reciprocal theorem of Stokes flow and exact solutions for a Newtonian fluid.

An experimental exploration of diffusive translational and rotational motions of elongated particles confined in a quasi-two-dimensional fluid is presented. Data obtained over 3 orders of magnitude in particle length demonstrate crossovers between hydrodynamical regimes determined by characteristic length scales.

A simulation of analyte preconcentration in a gated nanofluidic device finds that local field-effect control of surface properties can generate tunable ion concentration polarization regions in which anionic analytes are predicted to significantly accumulate if the electric double layers overlap.

In stochastic rotation dynamics the cubic interaction volumes induce artificial anisotropy, which can become significant in the vicinity of boundaries. A new study shows that this anisotropy can be avoided by employing randomly distributed, spherical interaction volumes instead of Cartesian grid cells.

In dense, inclined flows of spheres, particles are often observed to translate in layers. The forces and rate of momentum transfer associated with a process of rub, lift, fall, and bump are calculated, and a relation between the ratio of shear stress to normal stress and the rate of strain is determined.

Time-series tools are used to analyze how chaotic dynamics interacts with noise in the generalized Kuramoto-Sivashinsky equation, a prototype for falling films. The critical value of the noise intensity for the chaotic-stochastic transition is quantified in terms of the system control parameter.

The Koopman mode decomposition provides a fully data-driven framework for comprehensive dynamic analysis of complex flows. For example, the evolution of Koopman eigenvalues computed from data clearly indicates the sequence of bifurcations occurring in the state space of the flow.

When fibers are advected in a fluid flow, they organize into patterns dominated by scar lines across which the fiber orientation rotates by $\pi$. An exploration of the topology of the fiber orientation field in a 2D chaotic flow shows that scar lines form by a process of fluid stretching reversal.

Pressure fluctuations in unforced subsonic jets indicate the presence of linear wave packets in the near field. An interpretation in the resolvent framework shows that these signatures represent higher order near-field behavior that must be captured to obtain accurate far-field acoustic predictions.

Pocket events in the viscous sublayer of a turbulent boundary layer are shown to scale with the Taylor microscale. A simple model of a compact vortex propagating obliquely toward the wall from a position near the lower edge of the log layer is consistent with the observed scaling behavior.

A method is proposed to trigger inflow turbulence while minimizing spurious noise in order to study the noise radiated directly by a turbulent boundary layer. The strategy is based on a controlled transition by entering a resonant triad of unstable modes based on an inflectional velocity profile.

A spatially modulated generalization of Taylor-Green vortices is obtained for Cartesian, polar, and cylindrical systems that are exact analytical solutions of the Navier-Stokes equation. It is shown that a double array of Taylor vortices mapped onto a cylinder may also have radial modulation.

Trajectories of vortex pairs deflected by an inclined plate undergo topological discontinuities as the plate length or angle changes. In fact, the vortex winding number jumps in a self-similar fractal fashion across gaps within gaps within gaps ad infinitum, which trap the vortices.

An investigation of an $N$-vessel coupled sloshing system determines the existence of regions of parameter space where the $(N+1)$-fold $1:\cdots :1$ resonance can occur. These internal resonances are the precursors to the interesting dynamics in the nonlinear regime.