An experimental investigation in a novel tangential flow filtration geometry at a moderate Reynolds number reveals how the presence of a secondary flow can can modify inertial migration and focusing of microparticles.

A theoretical and experimental study of the linear and nonlinear instability of water bells is presented.

A model swimmer consisting of two linked spheres, wherein one sphere is rigid and the other is elastic is proposed. Despite reversible actuation of the connecting rod, it is shown that the elastic two-sphere swimmer propels forward in Stokes flow due to the deformation of the elastic sphere.

A generalized Navier-Stokes model for active fluids permits analytical Abrikosov-type vortex-lattice solutions, offering a potential explanation for recently reported ultra-low and negative viscosity states in bacterial suspensions.

Active particles in a passive medium is a ubiquitous motif in biology. A novel long-range attractive force between highly diffusive “hot” particles in a less diffusive “cold” bath is reported. The interaction range of hot particles in a cold bath can be more than 10 times the particle radius.

A stochastic kinetic theory is used to quantify hydrodynamic interactions among swimming microorganisms. The interactions alter the correlations and dynamics of organisms and the mixing of passive tracers. Tracers can exhibit superdiffusive motion even without interactions of the organisms.

The sensitivity of elongated voids in pressed explosives is analyzed with reactive mesoscale simulations. A strong dependence of the sensitivity on void aspect ratio and elongation is found. Ranges that enhance or inhibit initiation are identified.

Void collapse in solid explosives leads to hot spot formation and enhanced sensitivity. Here a grid resolution study is presented for a two-dimensional circular void for various shock strengths. We find that mesoscale simulations of voids may contain significant predictive uncertainty.

An investigation of nonuniform flow profiles in soft glasses of colloidal rods finds that plug flow and internal fracture occur at low shear rates, gradient-banding at intermediate rates, and uniform flow at high rates.

Autocatalytic reaction fronts between two reacting species propagate as solitary waves (from right to left here). A forced flow from left to right can balance chemical waves leading to frozen fronts.

Flow transitions for wormlike micelle solutions and solutions of linear polymers flowing around a microfluidic 90˚ bend are compared. The first transition in all fluids is at similar Weissenberg number, but the form of secondary flow and higher transitions depend on the wormlike micellar structure.

Bypass transition in wall-bounded flows is delayed upon addition of polymers. A torque is established by the polymer forces and opposes the local vorticity, thus weakening the amplification of streaks and delaying transition.

An investigation of the coefficient of restitution of bubble collision on a free surface in the presence of surfactants is presented. A reduced rebound velocity in the surfactant solution is observed and quantified using the Langmuir number, the ratio between absorption and desorption rates.

The extent of spreading of molten drops onto a cold substrate depends on substrate temperature. Experimental and theoretical results show strong evidence that the spreading of solidifying drops is arrested when liquid at the contact line reaches a critical temperature, which is determined by the effect of kinetic undercooling.

Evaporation of drops on flat substrates is studied for a pinned contact line and a moving contact line with a fixed contact angle. For the former, the local contact angle goes to zero prior to total evaporation. For the latter, the droplet keeps its initial shape and the contact line speed is constant.

The model in Part I is adapted for curved substrates. For periodic substrates, apparent contact angle is periodic and “apparent stick-slip” motion is observed. For quasiperiodic substrates, apparent contact angle is no longer periodic and contact line dynamics is not limited to apparent stick-slip.

Vortex shedding around a square cylinder at Re $=100$ is completely suppressed by plasma actuators installed on the rear surface, due to formation of a jetlike flow. The control effect is also predicted by a linear sensitivity analysis, showing good agreement with the full simulation.

Four terms in a weakly nonlinear expansion of the response of a round jet to harmonic forcing are Borel-summed to extend the range of validity.

Wavy surface variations establish separation bubbles on an unswept wing. The development of Tollmien-Schlichting disturbances are investigated, and PSE analysis is shown to agree with LNS solutions for some configurations.

By experimentally counterbalancing a pressure gradient with moving boundaries the subcritical transition to turbulence is studied in a shear flow with zero mean advection velocity. Nearly stationary turbulent structures result. Velocimetry is used to characterize the structures vs Reynolds number.

The effect of a peripheral slit on the wake dynamics and mean base pressure of an axisymmetric body is studied experimentally. The mean base pressure is found to increase monotonically with slit size until a saturation is reached. The main mechanism for this is an improved symmetry of the wake.

During coalescence of a drop with a liquid bath, the damped coalescence cascade (DCC) occurs due to local Marangoni flow generated on the bath surface. The local Marangoni flow accelerates air film drainage between the drop and the bath, leading to suppression of the rebound of daughter drops.

Shear rheology of a harmonically driven knife-edge viscometer is analyzed with experiments and computations. The distribution of phase lag in surface velocity relative to the knife-edge speed is shown to be a robust measure of the rheology over a wide range of driving frequencies and amplitudes.

Flow features for 2D falling films flowing under an inclined plane are presented based on the weighted integral boundary value model and compared with direct numerical simulations. For a transition to circulating waves, a universal critical ratio of maximum-to-substrate film thickness is found.

A new study shows that the need for slip models at interfaces and detailed molecular dynamics simulations can be obviated by continuum models that only require knowledge of the density, component mole fractions, and the dependence of the viscosity on the density

Three types of focusing positions over a tube cross section are experimentally and numerically found for spherical particles suspended in laminar square tube flows. The focusing patterns are classified into four regimes, depending on the Reynolds number for the particle-to-tube-size ratio ~ 0.1.

A general theory of the dynamics of an arbitrary magnetic object actuated by a rotating magnetic field is presented that rationalizes experimentally observed transport of geometrically achiral propellers. The propellers may acquire apparent chirality owing to the magnetic field and propel similarly to helices.

A dynamic model for LES is proposed to describe the motion of small inertial particles in turbulence. The model is simple, has low computational overhead, contains no adjustable parameters, and can be deployed in any type of flow solver and grid, including unstructured setups.

A novel methodology for efficient transport of heavy oil via a core-annular flow using a viscoplastic fluid is presented. In this triple layer structure, the viscoplastic fluid acts as an intermediate shaped skin layer to eliminate interfacial instability and balance buoyancy of the core fluid.

Curvature and torsion statistics of passive tracer trajectories are computed in two different types of rotating turbulent flows. How rotation influences the typical flow structures, both in the bulk flow and in the viscous boundary layers, is analyzed from these statistics.

Experimental measurements of the azimuthal motion of the large-scale circulation in turbulent rotating Rayleigh-Bénard convection reveal persistent flow rotation in an unprecedented large Rossby number range.

Hot-wire measurements were performed in a turbulent boundary layer overlying a complex, multi-scale topography to study inner–outer interactions. Similarities and differences of these interactions compared to smooth-wall flow are studied using amplitude and frequency modulation analysis.

Unstably stratified homogeneous turbulence is studied at very large Reynolds numbers with a spectral model for anisotropy. Anisotropic pressure spectra are similar to shear flows. At large Schmidt numbers scalar flux spectra scale as $k^{-1}$ beyond the Kolmogorov scale, after a transient $k^{-3}$.

Velocimetry is used to compare boundary layer and Large Scale Circulation structures in Rayleigh-Bénard cells with and without bottom plate roughness. Velocity fluctuations dramatically rise with roughness, and turbulence scaling changes. Roughness seems to lead to a turbulent boundary layer.

Vortex reconnections play a fundamental role in fluid dynamics. A study of reconnection events in superfluids using different vortex configurations is presented. By deriving asymptotic theory and using numerical simulations the universal and nonuniversal aspects of vortex reconnections are revealed.