We present a theoretical model with no free parameters to describe a class of turbulent fluctuations with an exponential tail in the probability density function. For turbulent thermal convection the model (solid line) is compared with measured temperature distributions (symbols), and agrees well.

We develop a tool for simulating three-dimensional locomotion in Stokes flow with highly resolved flow and swimming trajectories for multiple swimmers in the presence of surfaces. Key features include modularity, scalability, ease of implementation, and no need for mesh generation.

The gas-dynamical mechanism of ignition kernels formation in shock tubes is formulated on the basis of numerical analysis of the flow pattern developed behind the shock wave propagating in the rectangular tube filled with a reactive gaseous mixture.

Cercignani’s variational principle, originally derived for steady rarefied gas flows, is extended to unsteady flows exhibiting oscillatory time dependence. The utility of this theory is demonstrated by deriving approximate formulas and numerical results for Couette flow and Stokes’ second problem.

The evolution of heat flux through an initially solid pure substance that is heated from below and that undergoes both phase-change and natural convection is studied numerically and contrasted with the dynamics of the Rayleigh-Bénard system in laminar and turbulent regimes.

Reduction of the ambient pressure changes the boiling behavior of impacting ethanol drops on a heated substrate as observed by contact area measurements (insets). With decreasing ambient pressure, we find a widening of the transition boiling regime, while T${}_{Leidenfrost}$ stays roughly constant.

The cavity and central jet produced by the impact of a water drop on a water surface in a wind field are experimentally studied. Results show that the dynamics of the central jet are controlled by two mechanisms: the oblique impact caused by the wind and the wind drag directly acting on the jet.

Microdroplets are deformed and their transient relaxation in a microchannel is studied. By precisely analyzing the flow-induced stress on the droplets and their deformation, rheological properties are measured in situ.

A continuum model embedding thermal fluctuations, capillarity, and hydrodynamic effects is proposed to investigate bubble cavitation. The simulations, validated against molecular dynamics, access multibubble nucleation statistics and long-time dynamics in unprecedentedly large domains.

Concentration gradients in a fluid due to contrast in surface reactivity generate convective flows. An analytical model predicting the velocity magnitude in such flows is derived and verified against direct numerical simulation data over a wide range of parameters.

Various flow patterns and their evolutionary scenarios in three-dimensional electroconvection are numerically investigated. Specifically, a careful comparison of the hexagonal pattern is made to the previous semianalytical stability analysis results.

Motivated by the recent discovery of subsurface oceans on planetary moons, convective flows in shallow spherical shells set in rapid rotation are explored. A new equatorial beta-plane convection model that captures trapping of convection at low latitudes due to rotation is investigated.

Mixing layers can grow in time or space by vortex pairings that succeed each other in a nearly self-similar way. We use a point vortex model to study how confinement eventually limits this growth process, leading us to propose a wavelength selection mechanism for free shear layers with counterflow.

Eigenspectra and pseudospectra of the (turbulent) mean-linearized Navier-Stokes operator are used to characterize amplification mechanisms in laminar and turbulent flows in which linear mechanisms are important.

Tollmien-Schlichting (TS) waves are attenuated experimentally using a single-input and single-output feedback control system in real time. On implementing the controller, TS wave growth rates are shown to be suppressed significantly over a noticeably large domain.

The role of instability waves (IW) in free-stream turbulence (FST) induced boundary-layer transition in an adverse pressure gradient is studied with direct simulations. IW are found relevant even at moderate FST intensity of 2%. The effect of FST spectrum and intensity on transition are explored.

Evaporation of a binary liquid into vacuum is studied through a mean-field kinetic theory approach. It is found that evaporated atoms are distributed according to anisotropic Maxwellians, and evaporation coefficients are only mildly dependent on the liquid-vapor interface composition and temperature.

Impacting drops can be reflected by moving solid plates, provided the surface moves fast enough. The threshold speed of bouncing is described and modeled, along with the dynamics of liquid removal. Viscous or low surface tension liquids, usually impossible to repel, are thus efficiently swept away.

Classical pressure-impulse theory solution for water impact of a flat plate exhibits both singular initial fluid acceleration and a near-plate-edge singularity in the velocity field. Here the singularities are resolved by including effects of compressibility, viscosity, and surface tension.

Experimental observations of two-dimensional pinch-off of an air sheet surrounded by viscous liquid lead to an exactly solvable case of self-similar dynamics of a topological transition: Scaling functions for velocity and shape are both analytic and precisely describe experimental observations.

Liquid-infused surfaces have potential applications for drag reduction. A study of their effective slip length and robustness via a multiscale (nano to micron) numerical framework is presented, relating their performance to various design parameters.

Numerical experiments demonstrate that the laminar-turbulent boundary in pipe flow exhibits qualitatively different regions whose dynamics resemble that of the nearby unstable invariant solutions. In addition, various different state space paths to turbulence from this boundary are illustrated.

The mixing length growth in the miscible displacement through granular porous media is evaluated. Scaling laws are proposed to quantify the role of medium heterogeneity, viscosity contrast, and injection rate on the solution mixing.

In turbulent boundary layers, the wall-normal gradient of the Reynolds shear stress identifies momentum sources and sinks. The spacetime evolution of these small-scale motions is experimentally investigated in a turbulent boundary layer with time-resolved particle image velocimetry.

The accuracy of subgrid scale velocity kinetic energy models for reacting and nonreacting flows is studied using direct numerical simulation data. The analysis shows the dissipation of momentum, not taken into account in existing models, to be the key factor. A new model, localized diffusion-dissipation, is proposed on the basis of this result.

Length scale in a flow depends on the decryption key used to decipher length scales and the communications between them. Analysis shows that some of the decryption keys widely used can, in fact, obfuscate the physics, whereas one of them allows us to unravel the correct multiscale dynamics.

The statistical properties of the measurements performed by tiny self-propelled probes drifting in a turbulent flow are studied by means of a numerical model system. Their nontrivial combination of Lagrangian and Eulerian features are highlighted both in fluid velocity and scalar field time-series.

Rotations of large, neutrally buoyant, anisotropic particles in isotropic turbulence are studied. The rotation rate probability density function and its moments are found to be simple functions of particle shape and size. These are compared with structure functions in the flow to understand the effects of finite particle size.

The secondary flow in wide turbulent ducts is characterized by means of high-order direct numerical simulations. New results indicate that ducts or experimental facilities with aspect ratios larger than 10 may, if properly designed, exhibit good agreement with results obtained from spanwise-periodic channel computations.

We present wind tunnel and numerical experiments of the flow behind a model wind turbine in optimal and sub-optimal regimes. Spatio-temporal filtering and dynamic mode decomposition reveal that the onset and amplitude of wake meandering are affected by both the operating regime and the nacelle.

The return-to-isotropy of turbulence across scales is studied for different thermal stratification and surface roughness regimes from measurements in the atmospheric boundary layer and it is compared with predictions of a homogenous model.

The evolving topology of vortex lines during reconnection of vortex tubes is addressed. New features of the reconnection process are revealed, such as the generation of many small flux rings, and of vorticity null points. Methods to measure changes in flux connectivity are discussed.

Experiments are performed in a large basin to investigate nonlinear gravity waves generated by a periodic or a slowly modulated forcing. High-frequency self-similar spectra ascribed to bound waves are reported, which share similarities with the ones observed in previous experiments of wave turbulence.