An effective scaling exponent between the Nusselt and Rayleigh numbers of 0.42 is predicted for fully rough turbulent thermal convection in the ultimate regime. This is distinct from the value of 0.38 for smooth walls and from 0.5 for the asymptotic (infinite Rayleigh number) ultimate regime.

Near the freezing ice front in sessile droplets, air dissolved in the liquid water is observed to separate out to form many isolated bubbles, making the ice droplets porous media instead of tight ice beads.

A dandelion pappus is modelled as a porous disk. A stability analysis finds that if the disk is sufficiently porous the steady wake is stable and consists in a separated recirculating vortex ring, which allows a long-distance dispersal of the dandelion seeds.

Twenty-four small roughness elements in the boundary layer on a rotating cone trigger stationary vortices, which grow and saturate, followed by a rapid growth of non-stationary modes and a transition to turbulence.

A multicomponent lattice Boltzmann method with a force term for the effects of the near-contact interactions is applied to two droplets colliding and to emulsion production in microchannels.

Despite tremendous turbulent fluctuation in a high-Reynolds number Taylor-Couette flow, dispersed millimetric fibers show a preferred alignment with respect to the inner cylinder of the apparatus. Using a simplified model based on Jeffery’s equations, the orientation can be reasonably predicted.

The efficiency of the three-sphere swimmer is studied and the optimal actuation sequences determined. By accounting for full hydrodynamic interactions in the low Reynolds number regime, it is shown that, surprisingly, the swimmer with unequal spheres can be more efficient than the equally sized one.

Bubble removal from yield-stress fluids by ultrasound is studied theoretically by combining the governing equation of bubble dynamics with an elastoviscoplastic constitutive model. The radius of the yielded region oscillates at twice the frequency of the ultrasound-driven bubble oscillations.

We develop a coarse-grained Brinkman-type model for the dynamics of ordered arrays of immersed fibers. This approach provides a simple framework for the mathematical analysis and efficient numerical solution of problems including fiber-fluid rheology, soft valves, and waves within driven fiber beds.

Formation of an unusually extended wake behind a falling sphere in a shear thickening dilute micellar solution (CTAB/5mS) is reported. It is suggested that this behavior is linked to flow-induced micellar structure formation where micelles transition from rodlike to wormlike micelles around the falling sphere.

The interaction of a planar shock wave with grid generated turbulence finds that at first the turbulence increases the projection thickness of the shock and then at higher intensities fragments the shock.

Centrifugal buoyancy affects the flow structures and the heat transport in all rotating convective experiments. Numerical simulations are used to provide predictions of the centrifugal effects expected to arise in laboratory studies of the dynamically rich system of Coriolis-centrifugal convection.

A three-layer structure is proposed for a differentially heated vertical channel, based on the properties of force balance in the mean momentum equation. A three-layer structure is also proposed for the mean heat equation. A multiscaling analysis is developed for the inner and outer layers.

An experimental study demonstrates how surrounding gas affects secondary droplets ejected during splashing at high Weber and Reynolds numbers. It provides evidence that splashing is influenced primarily by the density, followed by the viscosity, and finally by the mean-free path of the gas.

The flow of two immiscible liquids or fluids in bounded systems where confinement geometry varies can lead to drop or bubble formation. A comprehensive experimental investigation on such an emulsification, or foaming process, occurring at the end of a glass rectangular tube is presented.

Direct numerical simulations are used to characterize the equivalent slip length at a spherical drop interface under Stokes flow conditions. An analytic form of the memory kernel for the force acting on a viscous drop is proposed and validated.

An inverse cascade of hybrid helicity is observed in direct numerical simulations of 3D magnetohydrodynamics with both an imposed magnetic field and a rotation rate. The impact of the tilt angle between the two axes and of the polarized forcing is discussed.

A theoretical analysis of the effect of an irreversible $A+B\to C$ reaction on the growth of a buoyancy-driven instability in a Hele-Shaw cell, taking different diffusivities into account, is presented.

Liquid sheets are essential for industrial applications, and during thermal drawing, a stretching viscous sheet breaks up into filaments. A theory is proposed to elucidate the underlying mechanism, shedding light on the sophisticated structures for functional devices in fibers, fabrics, or textiles.

The gradual expansion of large bubbles rising in a liquid-filled tube can become violent in the last few seconds before reaching the tube top. This process is responsible for Strombolian volcanic eruptions and for accidents in deep-water oil drilling such as the 2010 Deepwater Horizon explosion.

A computational study shows that the flow induced by a sphere rotating in an otherwise quiescent fluid is convectively unstable to spiral vortices, which once induced are swept down through the sphere’s boundary layer and then out into the radial jet that emanates from sphere’s equator.

Resolvent analysis predicts and direct numerical simulation confirms that the effectiveness of opposition control depends on the phase between sensor and actuator. The results confirm the capability of resolvent analysis as a tool for flow control design and raise interesting flow physics questions.

Temporal variations of the three-dimensional air-water interface shape of trapped air pockets on hydrophobic surfaces in turbulent flows are directly measured. Depending on the shape regimes, the corresponding diffusion rate of air pockets is modeled as a function of flow and geometric parameters.

A circular opening in a Hele-Shaw-type confinement gives rise to thermocapillary dipole flow, which can be used to drive flow in microfluidic configurations. The same mechanism can also be leveraged for the propulsion of light-actuated surface swimmers.

Streamwise variations in the cross section of liquid-infused substrates are shown to affect their ability to retain liquid when exposed to an external, immiscible shear flow, with potential implications for the design and manufacturing of omniphobic and drag-reducing surfaces.

Drag force due to polyethyleneglycol in a flow was measured by using a scanning probe microscope. The conformation of the polymer in the flow was predicted to have a stem and ellipsoidal-flower shape. The drag force due to the deformed polymers predicted by this model was calculated and confirmed.

Observations of the settling velocity of suspensions of irregular particles are found to depend on (i) the difference of density between the particles and the suspension and (ii) a viscosity which depends on the ratio of the concentration to the loose packing concentration.

Compared to fluid dynamics, granular material flow is poorly understood. Magnetic resonance imaging of poppy seeds flowing through three silos reveals three distinct flow regimes. A continuum mathematical model using an effective viscosity captures the dynamics in two of the three regimes.

Mixture-induced phase separation of an initially supercritical fluid due to the interaction with its surrounding is studied. Three different injection temperatures are investigated and qualitative characteristics of the formation process agree well between experiments and simulations.

Direct numerical simulations of settling and rising cubes show the prevalence of distinct helical motions, the onset of which are accompanied by a significant jump in the drag coefficient. This enhancement is associated with a combined effect of the vortex-induced drag and the cube orientation.

Mud is widely present in the environment and it can bind contaminants or nutrients. Since particles that make up mud are small and sticky, it is difficult to perform precise measurements. To this end, we present a numerical framework, which yields results that have so far been impossible to obtain.

A combined theoretical and experimental study is presented for rapid flow-induced compaction of a fibrous porous medium. The model is used to understand the dynamics of a standard test for pulp suspensions: the Canadian Standard Freeness test, which depends sensitively on the solid bulk viscosity.

The flow of a dense dispersion with short-range attractive forces is simulated. Discontinuous shear thinning occurs via rapid loss of particle-tangential viscous dissipation. The phenomenon is closely connected to discontinuous shear thickening, where tangential dissipation is due to solid friction.

We conduct experiments to examine the compaction dynamics of a liquid immersed granular packing under an upward flow which is either continuous or made up of repeated short bursts. We find that compaction is possible in the continuous case and compaction efficiency can be enhanced for short bursts.

We advance a new method to estimate the turbulent kinetic energy of the carrier phase in the presence of sub-Kolmogorov particles ${\epsilon }_p$. Our results suggest that particles affect the carrier phase turbulent cascade in a nontrivial manner at concentrations close to ${\varphi }_v={10}^{-5}$, and $R{e}_{\lambda }\in [200,600]$.

The sharp transition in flow behavior in turbulent weakly rotating thermal convection is explored with Lagrangian velocity and acceleration statistics of fluid particles. The transition consists of two distinct phenomena: 1) transition in heat transfer and 2) emergence of cyclonic vortical plumes.

In the late afternoon, the surface temperature drops below air temperature and the lower atmosphere’s density stratification becomes stable. A simple model that predicts the rate at which turbulence kinetic energy and mixing decrease after the onset of stable stratification is presented.

Large-eddy simulations are performed to study active flow control of deep dynamic stall for an SD7003 airfoil in plunging motion. For some frequencies, flow actuation disrupts the formation of the dynamic stall vortex, leading to drag reduction, while lift is almost unaffected.

Available direct numerical simulation databases are used to study the sensitivity of wall model predictions to different eddy viscosity models, damping function scalings, and associated constants. A new “mixedmin2” damping function scaling is proposed, which works better for high-speed flows over a range of conditions.

Experiments are conducted to study the effects of suspended sediment on flow dynamics in a mixing box. Results from particle image velocimetry, providing the velocity of the sediment and fluid phases separately, demonstrate the formation of a stratified layer where turbulent modulation increases.

An experimental study concludes that beyond $R{e}_{\tau }\sim 600$, the wall shear stress (${\tau }_w$) evolves to an asymptotic state in which the statistical moments, probability density function, and power spectra of ${\tau }_w$ become independent of Reynolds number.

Droplet size growth is usually enhanced by turbulence in the background air flow. Experimental measurements show the existence of an optimum air turbulent intensity for maximum droplet size growth in a polydisperse droplet field. The onset of clustering is shown to play an important role.

Numerical simulations of rotating convection as a simple model for atmospheric vortices show that the eye that forms at the center may become unstable and bifurcate into an oscillatory state. It is proposed that these oscillations result from a trapped inertial wave at the core.

The level of nonlinearity of experimental surface gravity wave turbulence is investigated. The measured average steepness of 10% is considered high. It is shown that the high nonlinearity of our flow is mainly supplied by bound waves, the free waves being in a weakly nonlinear state.

A study of periodic and chaotic flows in thin, rotating spherical shells at low Prandtl number finds that convection can be equatorially asymmetric and confined in one hemisphere near the onset, contrasting with previous studies. The applicability of these results to gas-giant atmospheres is explored.

Two surface waves are forced in a cylindrical tank. Their nonlinear interaction generates a third wave not obeying the dispersion relation, whose presence is shown using a laser vibrometer or a three-dimensional free-surface reconstruction. We explain this result as a forced three-wave interaction.

Quantitative boundary control of buoyant, interfacial dynamics between two high-viscosity-contrast Stokes fluids is achieved by the technique of characteristic tracking. This enables the experimental generation of desired wave breaking profiles that produce dispersive shock waves and solitons.

Laboratory experiments of floaters’ displacements in surface wave turbulence reveal that a combination of waves, eddies, and large-scale circulation team up to cause particle dispersion and preferential concentration. A simple physical model can reproduce all observations.