Direct numerical simulations of highly turbulent Rayleigh-Bénard convection up to Rayleigh numbers Ra = ${10}^9$ in horizontally periodic domains with aspect ratios up to Γ = 128, find superstructures of very large-scale and long living coherent structures.

We find that the consequence of switching off long-range hydrodynamic interactions in simulations of concentrated suspension is that they can be switched off if considering the viscosity, but not if considering the diffusivity or particle velocities.

The swimming efficiency of an idealized microswimmer is theoretically examined where the pointwise viscosity depends weakly on the surrounding nutrient. Results show that optimal swimming efficiency is achieved differently in the constant- and variable-viscosity cases.

A novel approach for modeling the scalar flux term in turbulent flames is presented. An iterative algorithm is used for “deblurring” the filtered field. Successive iterations lead to improved approximations of the original field, and explicit filtering is then used for modeling the scalar flux.

Flow transitions in the settling of a sphere in non-shear-banding wormlike micelle solutions are mapped. The onset of unsteady sedimentation correlates with an extensional Deborah number, while the velocity fluctuations are related to a shear Deborah number and an elastic Mach number.

Penetrative convection is essential in controlling the dynamics of many geophysical and astrophysical systems. Here, we explore how a nonlinear vertical density profile influences the penetrative convection into a stable stratification.

Original numerical simulations of 2D turbulent convection on a hemisphere are presented. Nusselt and Reynolds numbers verify scaling laws consistent with Rayleigh-Bénard convection. Despite significant differences in geometry with classical 3D cells, the scaling laws of thermal convection are robust.

The effect of inclination on the sodium (Pr=0.0094) turbulent convection in a cylinder of unit aspect ratio was studied experimentally for a fixed Rayleigh number Ra$=(1.47\pm 0.03)\times {10}^7$, and the inclination angle varied from 0° (the Rayleigh-Benard convection) up to 90° with a step of 10°.

Microscopic bubble dissolution is driven by the diffusion of gas within the surrounding liquid. Asymptotic analysis is used to characterize collective shielding effects in bubble lattices, the resulting bubble lifetime and dissolution dynamics.

Simulations and experiments resolve a long-standing controversy that the gradient of surface tension—Marangoni stress—rather than surface tension lowering is responsible for decelerated thinning rates and microthread cascades during breakup of surfactant-covered threads.

The numerical and analytical investigation of elastic capsules filled with a ferrofluid/dielectric liquid in a uniform magnetic/electric field shows a discontinuous spherical-to-conical shape transition for increasing fields with diverging strains in the conical tips.

An electrohydrodynamic flow in a point-to-ring corona configuration is investigated experimentally and numerically. A parameter $X$, defined as the ratio of the local electric force to the inertial term, characterizes the effect of electrohydrodynamic forcing on bulk flow.

In an experimental and numerical study, a magnet floating in a thin electrolyte layer is dragged and accelerated by a vortex dipole generated by a Lorentz force. Vortex shedding appears when a sufficiently high electric current is applied, promoting a zigzag magnet motion.

Using candy “landforms” carved and reshaped by flowing water, laboratory experiments show how it is that some shapes keep a memory of earlier conditions as they develop while others forget the past, a fact that is important in geological dating and understanding how landscapes form.

We evidence two regimes for the flapping instability of a liquid jet atomized by a gas stream: a first one where it is synchronized with an upstream shear instability, and a second one where frequency is independent of gas flow, simply controlled by the ratio of liquid velocity to liquid jet radius.

How does a liquid-vapor interface in contact with a plate in motion react to the presence of defects at smaller scales? The hydrodynamics of such a system is investigated theoretically, offering a tractable mathematical framework to explore contact line motion through a disordered energy landscape.

Pattern formation processes in magnetic fluids confined in a Hele-Shaw cell and subjected to a radial magnetic field are studied. It is shown that the weakly nonlinear flow drives an initially circular interface towards nontrivial exact stationary shapes, which are dynamically stable.

Fluid inertia is usually ignored in network models used to predict flow in porous media. A model based on an averaged Navier-Stokes equation, validated for displacements in straight capillaries, is shown to capture the effects of inertia. Results suggest it can form the basis for more realistic network models.

The effects of higher-order force moments of active particles on the flow field induced by their motion are investigated. Using the reciprocal theorem, explicit expressions for the stresslet dipole, rotlet dipole, and potential dipole of an arbitrarily shaped active particle are provided.

Magnetic resonance imaging is used to map out velocity fields during fluid flow in a clear channel coupled to a permeable wall. The maps are compared to lattice Boltzmann modeling to demonstrate that the velocity fields can be simulated without analytical expression of the boundary velocities.

We define effective pore size as a function of the porosity, the tortuosity, the contraction factor, and the intrinsic permeability of the porous medium. The Klinkenberg effect in different porous structures is found to be fully described by the Knudsen number characterized by this pore size.

The acoustic streaming flow in microchannels and nanochannels caused by complex fluid-structural coupling due to surface acoustic waves is studied using a hybrid continuum and mesoscale numerical model.

Hydrodynamic interaction between two adjacent waving elastic filaments is examined analytically and experimentally. Results show that antiphase beating is optimal for propulsion, hydrodynamic interaction modifies the optimal Sperm number, and phase difference between the filaments enables maneuvering.

Buoyant particle suspension in a horizontal rotating cylinder is known to exhibit axially oscillating particle bands in the centrifugal force dominant phase. Numerical simulations using Stokeslets as the particles were performed to investigate the behavior.

New experiments show that collisions between a sphere and a plane immersed in a viscous fluid involve direct mechanical contact, in contrast to expectations based on earlier theory. An electrical probe is used to monitor short-time mechanics of contact formation during the rebound of the sphere.

In a study of inertial particle velocity gradients and the corresponding flow topology, the density weighted joint distribution shows that converging saddle structures are most probable.

Inertial particles moving in a fluid flow are ubiquitous in nature. Despite their small size, they can actively influence Earth climate dynamics. A new perturbative strategy is proposed to obtain the sedimentation velocity and the effective diffusivity in the limit of neutrally buoyant particles.

Drag reduction and interfacial robustness of turbulent flows over superhydrophobic surfaces with randomly distributed textures are investigated using direct numerical simulations. Slip length, pressure fluctuations, and interface deformations are analyzed and compared against aligned textures.

The feedback between topographically driven turbulent secondary flows and modulation of small-scale amplitude and frequency is explored. Results demonstrate that modulation remains but differs intrinsically because of background secondary flows within the domain.

An experimental investigation shows that the small ellipticity of a precessing spheroidal cavity has a significant impact on the flow transition from solid-body rotational flow to developed turbulence of a confined fluid. In contrast, the developed turbulence in the spheroid is almost identical to that in the sphere.

A detailed study on the scale dependence of various quantities of interest, such as the population fraction of different flow-topologies, is presented. While the quantities appear close to scale invariant in inertial range, a “bump” is observed at length scales between the inertial and viscous ranges.

Direct numerical simulations of flow over fourteen dense rough walls with varying geometry are conducted. The effect of a departure from same-size element roughness on turbulence statistics is studied, and the correlation of the roughness function with wall-normal fluctuations at the roughness crest is examined.

The interaction between wall-mounted, flexible plates and wake fluctuations is experimentally investigated as a function of several geometrical and flow parameters. It is demonstrated that significant decoupling between the dynamics of the structures and flow may occur because of near-wake flow instability.

Experiments are performed in the Coriolis facility to investigate gravity surface wave turbulence. Results indicate that dissipation is responsible for the quantitative discrepancy between experimental and field measurement of the wave energy spectrum, which is systematically steeper in the lab.

Linear models are often used for the evolution of capillary jets. Here we present the simplest linear spatial formulation and compare it to numerical simulations. Two magnitudes, shape deformation, and mean axial velocity, and two spatial modes are needed, with one of them decaying exponentially.