Identity equations are derived for the global turbulent kinetic energy (TKE) and temperature variance production. Shear-produced TKE is found to scale as $u_{\tau }{U}_{\max }^2$ and buoyancy-produced TKE scales as $u_{\tau }^2{U}_{\max }$. Scalings for temperature variance production and dissipation are also revealed.

Contact angle hysteresis is measured on micropillar surfaces with four different area fractions. To fit the data at higher area fractions, the Cassie law is modified to account for capillary bridges.

Time-evolving coherent structure with features consistent with Townsend’s attached eddies and the developments associated with the reconstruction of flow statistics using the attached eddy hypothesis can be obtained from analysis of the (linear) resolvent associated with the Navier-Stokes equations.

Large-eddy simulation is used to study turbulent airflow in anatomically accurate rhesus macaque airways along with the transport of microparticles in the flow. Microparticle deposition predictions are compared with model experiments in the same computed-tomography-based airways.

Laboratory experiments were conducted with synthetic magnetic helical swimmers to study the dynamics of crossing the interface between two immiscible fluids. This system aims to emulate the process through which bacteria are capable of penetrating mucus layers or membranes to cause infections.

Using adaptive numerical solutions of the reactive Navier-Stokes equations we clarify the mechanism of detonation stabilization in supersonic expanding channels, and further demonstrate that by dynamically controlling a moving boundary dynamically stationary detonation propagation is possible.

Polymers make flow in a tube unstable at low Reynolds numbers. An investigation shows that laminar flows of polymer solutions in a tube become unstable, unlike Newtonian fluids, at a Reynolds number as low as 10. This occurs because of the elastic and shear-thinning nature of polymer solutions.

Flow of Bingham fluids is unstable if channel walls are deformable. Laminar flows of Bingham fluids in rigid-walled channels are stable to tiny disturbances. A study finds that if the walls are made deformable, the flow becomes unstable at very low Reynolds number.

Fluid elasticity opposes inertia, creating a static hump and a cusp ahead of it on the film free surface. Nonlinear phenomena, such as resonance of the liquid film with the bottom undulations, are intensified or suppressed by the presence of shear-thinning and elasticity.

Stability to linear disturbances of arbitrary wavelength is studied using Floquet theory. Fluid elasticity stabilizes the flow and creates a small window where all disturbances are damped at supercritical conditions. Shear-thinning is destabilizing and may generate disturbances of wavelength shorter than that of the geometry.

Thermal counterflow of normal and superfluid components in superfluid helium leads to a form of turbulence confined to the superfluid component. Contrary to usual assumptions, these vortex filaments are shown to induce a strongly nonuniform flow in the normal fluid, even at small flow velocities.

An experimental study finds that when a drop impacts close to the edge of a surface, part of the lamella spreads out of the surface. Depending on the normalized distance to the edge, the free lamella can either recede back onto the surface, or completely break off at the surface edge.

The impact dynamics of a ferrofluid droplet on a tempered glass surface in the presence of a vertical magnetic field has been investigated experimentally. The results show how precise control of the impact dynamics of a ferrofluid droplet can be obtained.

Leidenfrost drops on curved substrates exhibit complex shape-change dynamics, which include polygonal modes, star modes, and a dominant large amplitude $n=2$ mode. Remarkably, two distinct modes are observed to coexist in stable synchronized resonance with harmonically related frequencies.

At large magnetic Reynolds numbers, magnetic induction leads to enhanced viscosity of mean shear flows. This effect is derived through simple physical arguments and verified in numerical simulations.

Electroconvection in dielectric liquid is extended from single phase to solid-liquid interaction. Stability criteria and bifurcation are numerically predicted by the lattice Boltzmann method. Effects of interface position, permittivity and mobility ratios, and electric conductivity are considered.

We discuss how to include surface tension in viscous thin film flows such as the circular hydraulic jump. We show that an energy term previously proposed can lead to a large overestimate of the influence of surface tension.

We find exact similarity solutions of the Navier-Stokes equations for the steady laminar flow of two immiscible, uniformly rotating fluid layers. For layers which counter-rotate too strongly a self-similar solution does not exist, as given by a condition we find on the angular velocity ratio.

Wind blown at very viscous liquid surface generates a small amplitude wave packet which sporadically forms large-amplitude fluid bumps rapidly propagating downstream. These viscous solitons, emitted in a region of large shear stress, are sustained by the wind and propagate in a lower stress region.

A study revisits the dynamic Wilhelmy plate method for measuring dynamic contact angles and proposes a more accurate model for the shear stress and viscous drag force. This drag force model is validated with particle image velocimetry and is applied to obtain dynamic contact angle measurements.

The drag of perforated thin disks is studied at low Reynolds numbers via displacement controlled experiments and simulations. It is shown that the drag of the disks is affected by the size of the voids, but not by the disk thickness. Good agreement is observed with existing analytical solutions.

The time-dependent spreading behaviors of a rinsing liquid across a horizontal, rotating substrate pre-coated with thin liquid films is investigated. Four distinct growth behaviors in time of the azimuthally averaged spreading radius are observed and explained with lubrication theory.

Temperature gradients affect fluid interfaces by changing the local surface tension. Both experiments and numerics show that in rotating thin liquid films, these Marangoni stresses significantly affect fluid film height profile dynamics and equilibria.

The Stokes flow created by regularized stokeslets (point forces) is analyzed. The authors determine the error made in the approximation compared to the singular solution, show how a source dipole appears generically in the far field, and propose an improved regularized solution.

Hydrodynamic interactions between droplets and high-viscosity fluid threads are investigated in microchannels. A complementary approach is adopted where the thread size is varied for diverse droplet concentrations to help reveal a range of basic fluid structures.

A thermal analysis shows that even without an imposed temperature drop, a gas-expansion-induced transient temperature decrease can slow viscous gas drainage from a semisealed channel with adiabatic walls. At given density drop, gas drains out faster as initial-to-final temperature ratio increases.

For a sufficiently deep microchannel, both experiments and simulations show a distinct transient nonmonotonic behavior of the system chronopotentiometric and chronoamperometric responses, resulting from the emergence of electroconvective instability in the overlimiting conductance regime.

Numerical simulations of turbulent multifluid flows, undergoing changes of the interface topology, are carried out using a front-tracking–finite-volume method. The results for varying void fractions show that the flow starts to depart from the bubbly regime at a void fraction of about 15%.

An experimental study of the motion of a self-propelled helix in granular matter shows that there is an optimal pitch angle at which the swimming speed reaches a maximum value. The measurements are compared with predictions with granular resistive force theory, leading to good agreement.

A pore size gradient dramatically alters the pathway taken by a nonwetting fluid as it flows through a porous medium. Microfluidic experiments and pore-network modeling elucidate how this behavior depends on the competition between the gradient and pore-scale disorder.

Flow reversals in natural convection of particle-dispersed two-phase flow in a two-dimensional square box are studied by numerical simulation. The thermal effect of particular particle alignments is modeled and found to be a precursory indicator of the reversal events.

The bouncing of a rigid particle off a soft coating in a viscous fluid is analyzed. The coating thickness moderates the degree to which elasticity affects the rebound criteria (and vice versa) in a fashion distinct from the effect of the elasticity or of the Stokes number.

The loss of buoyancy because of dissolution is mitigated or enhanced by changes in ambient liquid density. A scaling analysis identifies three parameters: dissolution rate vs plume rise time, the effect of dissolved material on liquid density, and the drop or bubble rise velocity vs the plume velocity.

We study experimentally an oil-in-water emulsion exposed to salt concentration gradients. Numerical and analytical studies elucidate the vertical and azimuthal flow instabilities caused by competing effects of the dissolved salt and the suspended oil droplets on the density of the medium.

A simple proof of the Kelvin Theorem, namely conservation of circulation (CC) for solutions of the Euler equation, is given. The result is rewritten in terms of time rescaled variables leading to the Euler-Leray equations, and the implications of CC on the existence of self-similar solutions are discussed.

Particle image velocimetry measurements are performed to examine the spatial structure in boundary layers under the influence of free-stream turbulence (FST). A similarity of the structural organization inside the boundary layer is found between the present FST cases and the canonical flows.

A relatively extensive survey of published data shows that the 4/5 law has not yet been observed in either experiments or simulations because the Reynolds number is not sufficiently large.

Reversed initial fields can generate nonequilibrium decaying turbulence. During the short time interval when the reversed flow reorganizes to restore its energy cascade, a new dissipation scaling is observed, $C_{\epsilon }\sim {\mathrm{Re}}_{\lambda }^{-2}$, for a nonequilibrium transient with rapidly evolving dissipation.

Evidence of the presence of vortical and thermal interfacial layers in transcritical turbulent channel flow is presented. These interfaces are tied to the uniform momentum zones. In an analogous manner, uniform thermal zones are defined and characterized in these complex flows.

Experimental and numerical investigations find that in a wide-gap turbulent Taylor-Couette flow, $N{u}_{\omega }$ features nonconstant effective scaling with $R{e}_S$ due to the curvature-dependent limited capacity of the outer cylinder to emit plumes. For counterrotation, strengthened turbulent Taylor vortices cause a torque maximum at ${\mu }_{max}$=-0.123.

Shear turbulence is simulated using numerically efficient triply periodic computational domains. The simulations focus on velocity fluctuations and achieve statistically stationary homogeneous shear turbulence. The numerical results agree well with experiments and simulations of free shear flows.

In fluid turbulence, enstrophy fluxes are associated either with velocity-to-vorticity transfers (vorticity stretching) or with vorticity-to-vorticity transfers (vorticity advection). In the inertial range, the four fluxes due to vorticity stretching are found to be larger than the one due to vorticity advection.

Experiments and simulations are combined to study flows in a T-mixer with offset inlets, whose stability is coupled to the vortex breakdown structure in the system. This leads to an unexpected flow regime in which increasing the flow rate can re-stabilize steady-state solutions of the flow.

The boundary layer over a cone rotating in a still fluid is investigated. A self-similar correction to the classical von Kármán solution, taking into account the effect of the outer flow, is proposed and validated. Finally, the stability properties of the corrected base flow are assessed.

Simulations of large-Reynolds-number stratified wakes reveal dynamics of a strongly stratified regime where thin flow layers form under stratification. Shear instabilities develop between the layers and drive turbulence. The ability to predict whether this novel regime is accessible in a wake of given parameters is demonstrated.

The effect of shear currents on rogue waves on a free surface is modeled by the nonlinear Schrödinger equation. Curvature of velocity profiles (or vorticity gradient) and the relative motion of the wave packet and shear current play critical roles, through enhanced growth rates of disturbances.