While droplet impact on liquid pools is well studied for Newtonian fluids, particle suspensions introduce complex non-Newtonian dynamics. This work experimentally identifies five distinct impact regimes for cornstarch suspension droplets, revealing unique phenomena like “wrapped bubbles” and impact-induced jamming that are absent in simple fluids. Through an energy balance analysis, the authors demonstrate that these behaviors are dictated by a direct competition between pool cavity dynamics and suspension rheology. The resulting transition boundaries offer practical guidance for engineering applications like 3D printing.

The interactions between flow structures and thin sheets of large polymer stress are investigated for a steady arrowhead coherent structure in a two-dimensional viscoelastic channel flow. We show that expressing the polymer body force in a coordinate system associated with stresslines, lines tangential to the stress principal axes, allows for an intuitive interpretation of these interactions. Approximating a polymer stress sheet by a stressline, across which the solution is discontinuous, we provide an expression for the jump conditions and show that the pressure difference across a polymer stress sheet is directly related to the local curvature of the stressline, and thus of the sheet.

The characteristic fanning out of spray clouds, whether spraying perfume or spray painting, is familiar. We studied spray cloud formation for parallel jet nozzles as a function of the pressure of the surrounding air. Our microfabricated nozzles with parallel 4μm holes produce multiple microjets; we find that these form conical spray clouds via air friction through a Kelvin-Helmholtz instability. As a consequence, if the air pressure is lowered in the transparent vacuum chamber in which we perform our experiments, the spray cloud disappears altogether. As shown in the figure, below a critical air pressure characteristic of the instability, the jets then simply propagate in straight lines.

Lattice Boltzmann models for nonideal fluids rely on mesoscopic force formulations whose connection to microscopic physics remains unclear. By constructing lattice Boltzmann distribution functions directly from molecular dynamics simulations, this work provides a framework for assessing force models against microscopic particle behavior. The analysis shows that a balanced combination of pseudopotential and free-energy formulations best reproduces the moments of the molecularly derived distribution functions, establishing a direct link between microscopic dynamics and mesoscopic fluid modeling.

Most insects generate forward thrust by tilting the stroke plane or adjusting the wing angle of attack. This study reveals that mosquitoes adopt a fundamentally different strategy: while maintaining a nearly horizontal stroke plane, they achieve forward flight through highly asymmetric wing pitching between downstroke and upstroke. Two novel thrust mechanisms are identified under this motion pattern—asymmetric pitch-down acceleration and asymmetric pitch-up amplitude. These findings deepen our understanding of insect flight diversity and offer new design principles for micro flapping-wing vehicles.

Choanoflagellates, key marine microscopic filter feeders, display large diversity in their filter geometry. Comparing a simplified infinite cylindrical model for the filter with biological, we find that many choanoflagellate species exist near a ridge in the effective flux into the filter but away from a similar ridge in the power. This contrasts with the existing hypothesis that the pressure drop is roughly constant over different species.

Collective locomotion of swimming and flying animals is fascinating in terms of individual-level fluid mechanics and group-level structure and dynamics. Here we bridge and relate these scales through a formation-flight model that views the collective as a material whose properties arise from flow-mediated interactions among its members. Our model shows that the group behaves as a soft “crystal” with regularly spaced member “atoms” whose positioning is susceptible to deformations and dynamical instabilities. Other emergent properties relevant to biological collectives include group cohesion, sensitive detection of and response to perturbations, and information transfer through traveling waves.

Soot formation in aero-engine combustors is influenced by coherent structures of confined turbulent swirling flows. This work combines large-eddy simulation with state-of-the-art soot models and spectral Proper Orthogonal Decomposition (POD) to identify flow dynamics directly from raw transient data. The results reveal a scale-dependent response: Polycyclic aromatic hydrocarbons (PAH) are mainly affected by high-frequency processing vortex core motion, whereas soot is governed by low-frequency dynamics. Dilution jets weaken high-frequency flow motions and modify the coupling among coherent structures, gas-phase precursors, and soot evolution.

We propose a moment gas kinetic flux solver (MGKFS). Like conventional GKFS, the governing equations for mass, momentum, and energy are still solved by the finite volume method (FVM). In addition, a set of evolution equations for stresses and heat fluxes are also solved by FVM, in which numerical fluxes are evaluated by high-order moments of the distribution function at cell interfaces. That is, high-order moment equations are directly computed via moment integration of a reconstructed gas distribution function at cell interfaces. This strategy not only provides a new closure method for the 13-moment system, but also avoids tedious boundary conditions for stress and heat flux equations.

The Oberbeck–Boussinesq (OB) approximation underpins much of our understanding of thermally driven flows, yet its validity in coldwater systems remains largely unexplored. Using numerical simulations of ice-bounded horizontal and vertical convection, we show that temperature-dependent material properties significantly modify flow structures and global transport, even where density variations are weak. In some cases, they induce anomalous reversals between warm and cold circulations, leading to O(10%) errors in predicted heat fluxes and ice melt rates, highlighting the non-negligible role of thermophysical variability in cryospheric waters.

Rayleigh–Darcy convection (RDC) in porous media controls mass and heat transfer in many geological systems. We show that permeability heterogeneity fundamentally reshapes RDC. The permeability correlation length interacts with intrinsic flow-structure scales that determine the convection pattern. High-resolution simulations reveal three distinct heterogeneity regimes depending on Rayleigh number (Ra): (i) At low Ra stable convection cells are constrained; (ii) At intermediate Ra microplume-driven transport is enhanced; and (iii) At high Ra heterogeneity becomes negligible or boundary-layer-controlled. This provides theoretical support for predicting convective mixing and scalar transport.

Turbulent thermal convection often organizes into large-scale flow structures that control heat and momentum transport, yet their dynamics in very wide systems remain largely unexplored. Using a liquid-metal Rayleigh–Bénard convection experiment with an extreme aspect ratio of 25, we demonstrate that jump rope vortex dynamics persist even within turbulent convective superstructures. The observed oscillatory behavior follows the same scaling laws previously identified in much smaller systems, indicating that jump rope vortex dynamics are not confined to specific geometries but remain relevant even in spatially extended convection at extreme aspect ratios.

Ferrofluid droplets deform under the competing action of flow, surface tension, and magnetic stresses, making ferrofluid emulsions promising magnetically tunable complex fluids. We develop an analytical small-deformation theory for droplets in general linear flows and uniform magnetic fields. The theory captures the coupling between flow and field, predicting shape evolution, droplet breakup, and the rheology of dilute emulsions.

Elongated bubbles in microchannels offer a promising yet still poorly quantified route to enhance convective heat transfer. We develop a one-dimensional model capturing the interplay between advection, diffusion, viscous dissipation, and wall heat flux in the thin film around the bubble. The results reveal scaling laws for the Nusselt number, linking thin-film flow dynamics directly to heat transfer efficiency.

The authors find that micrometric droplets heated up by strong irradiation exhibit a reversal of the classical diffusive evaporation: the speed at which they shrink slows down instead of speeding up. Using laser trapping, they measure tiny levitating droplets and see an initial deceleration in the shrinking decelerate followed by a return to the classical evaporation behavior below ~4 μm. This behavior can be explained with an scaling argument based on volumetric heating. The results show a new facet of irradiative evaporation of aerosols and fuel droplets in combustion systems where droplets can be strongly irradiated by flames or sunshine.

We experimentally investigate the detachment of a bubble injected from an orifice on a horizontally moving plate. By performing theoretical analysis based on force balance without empirical constants, we introduce a dimensionless parameter $R_c$ that characterizes a transition between vertical buoyancy-dominated “rise” and horizontal shear-dominated “lift-off” regimes. $R_c$ successfully captures the trends of both the bubble radius and inclination angle at detachment across all experimental conditions, and $R_c$ = 0.8 indicates the transition boundary between the two regimes.

Following the report of numerical evidence of a finite-time singularity in the wall-bounded three-dimensional axisymmetric incompressible Euler equations, we investigate the effect of a magnetic field on this singularity. We find the HL-type singularity as well as a new “cusp”-type singularity where the nature of the singularity is sensitive to the initial strength of the magnetic field relative to the kinetic fields. This study marks the first numerical evidence for singularities in the Ideal MHD equations in a wall-bounded domain.

Electrokinetic transport at liquid-liquid interfaces offers new routes for active microfluidic control, but practical use on slippery liquid-infused surfaces (SLIS) remains limited. Using direct numerical simulations, this work reveals two key regulation mechanisms, includign electroosmotic velocity reversal driven by groove oil depletion and a two-sided streaming potential effect from ion partition. These findings provide design principles for enhancing liquid pumping, energy conversion, and lab-on-a-chip devices in real-world multiphase systems.

The von Kármán sodium experiment provided the first laboratory observation of magnetic field reversals reminiscent of those occurring in planetary dynamos. Using realistic numerical simulations robust across two independent solvers, we identify the mechanism underlying these reversals. The dynamics result from the coupling of dipolar and quadrupolar magnetic modes through two large-scale velocity modes, one of which breaks the flow symmetry. During a reversal, the magnetic field first localizes near one impeller, then evolves through a transient quadrupolar state before localizing near the opposite impeller and ultimately recovering as a dipole of reversed polarity.

Granular flows interacting with obstacles are central to geophysical hazard mitigation, yet the post-impact evolution on horizontal run-out zones remains underexplored. This experimental study reveals a converging granular front formed downstream of a single cylinder along with volume‑dependent regime transitions from shock‑induced bifurcation to rapid stabilization. Scaling laws for front velocity, run up height, and centroid displacement demonstrate that initial column geometry and basal friction dominate over obstacle size and particle diameter. These findings decouple local flow perturbations from bulk deposition, providing predictive insights for designing barriers in confined terrains.

Subcritical transition in shear flows arise from the interplay between linear non-modal amplification and nonlinear interactions, yet their quantitative connection remains unresolved. We bridge this gap by deriving a framework from the Navier–Stokes equations, in which a forcing-amplitude expansion links oblique disturbances to finite-amplitude streaks consistent with direct numerical simulations. This hierarchy shows that the same resolvent structure governing linear amplification organizes the dynamics at all orders in the perturbation series. Breakdown of this series marks the onset of secondary instability, providing a quantitative bridge between non-modal growth and classical transition theory.

This work develops a linear model under a “total transmission” condition that isolates adjacent and cross-interface couplings in a three-interface system by suppressing reverberating waves. We then demonstrate bidirectional modulation of interface evolution by layer spacing and initial amplitude, showing that coupling can either stabilize or destabilize interfaces. Finally, we analytically derive “freeze-out” criteria for single-interface stagnation via parameter tuning and validate it numerically. These results advance multilayer Richtmyer-Meshkov instability physics, provide control strategies for shock-accelerated mixing in inertial confinement fusion, and impact reflected-wave studies.

We study the linear dynamics of an incompressible gas bubble in a biaxial straining flow, characterized by two stretching and one compressing directions, in the presence of finite inertial effects. The system undergoes a saddle-node bifurcation and exhibits strongly different equilibrium shapes when varying the Ohnesorge number comparing viscous and capillary effects. Linear stability analysis reveals the rich dynamics of the system. Bubbles are found to be significantly more stable in biaxial than in uniaxial flows, which may explain why turbulent breakup mainly occurs in uniaxial regions despite biaxial regions being more common.

This study investigates how nonlinear Langmuir adsorption modifies the transport, deformation, and viscous fingering dynamics of a finite miscible solute blob in porous media using a high-resolution Fourier pseudospectral method. The solute’s upstream advection speed decreases with increasing adsorption nonlinearity. The results show that adsorption can suppress or reintroduce viscous fingering, producing lump, comet, and fingered morphologies. Mixing exhibits nonmonotonic behavior at moderate viscosity contrasts, but increases monotonically for larger viscosity contrasts.

Large-aperture telescopes are currently limited by launch vehicle constraints. The Fluidic Telescope (FLUTE) concept seeks to overcome this by using liquid mirrors which, in microgravity, naturally relax into a precise spherical shape. However, necessary telescope maneuvers subject the liquid to body forces that perturb this interface. This study provides an experimentally validated analytical model for such liquid dynamics by solving for the non-self-adjoint problem of a thin liquid film pinned in a circular domain. Using the model to simulate decades of operation, we show that while edge disturbances build up, the inner 80% of the aperture remains optically precise for over 20 years.

We study a fluid close to its critical point where the liquid-vapor phase boundary ends and the distinction between gas and liquid disappears. The compressible Navier-Stokes-Korteweg equations are solved with a van der Waals equation of state. Density-stratified basic states due to gravity are computed numerically. Numerical simulations confirm the propagation of acoustic waves in the supercritical case above the critical point. For the subcritical case we find spinodal decomposition for a randomly distributed initial density. Additionally, we consider the Rayleigh-Taylor instability in detail, both by a linear stability analysis and by direct numerical simulations.

Hydrodynamic metamaterials can steer liquids without disturbing surrounding flow, but passive designs have largely been limited to fixed environments and regular geometries. We show that extreme effective viscosity anisotropy, realized through simple microchannel height modulation and solid barriers in Hele-Shaw flows, decouples a metashell’s performance from the background viscosity. The resulting free-form metadevice remains invisible under environmental changes while accelerating flow in its core, as verified by simulations and experiments, opening a route to robust microfluidic control.

This study investigates a novel fluid–flexible filament system in which the filament is allowed to move laterally in a uniform flow. Once symmetry breaking occurs, the filament exhibits spontaneous and sustained translation, effectively self-propelling by extracting energy from the flow. The dynamics are governed primarily by the effective Reynolds number and effective bending stiffness. A reduced-order parameterized model is further developed to predict the filament’s equilibrium configuration and curvature.

Resolving the near-wall motion of self-diffusiophoretic Janus particles is numerically challenging because of the steep solute concentration gradients within the narrow gap. We develop an asymptotic theory in the distinguished limit where the inert face is comparable in size to the lubrication region. For axisymmetric and slightly tilted configurations, we obtain explicit particle velocities and gap concentration fields that reveal how cap size influences the particle’s rotational stability near the wall.

Hair-covered appendages serve a variety of purposes in Nature, from chemical sensing to drag generation. To understand how these natural systems control flow, we study how confinement, porosity, and Reynolds number affect flow through and around a finite array of cylinders, using a combination of experiments and numerical simulations. Our results show that the confinement focuses the flow in the array and shifts the domains of existence of the flow regimes. We perform a theoretical analysis based on Sampson flows through rectangular slits to predict the flow rate through the array. The model is quantitatively consistent with the numerical results.

The influence of a temperature-dependent viscosity and wall slip are considered for high-Reynolds-number flow over a heated flat plate. In the limit of a small dimensionless slip length, which serves as a perturbation parameter, similarity solutions are developed. The results are used to study the combined effect of temperature-dependent viscosity and wall slip on the coefficients of friction and the Nusselt number. For example, the asymptotic solutions show that the slip contributions to the flow are enhanced by temperature-dependent viscosity.

Electroosmotic transport in soft microchannels is often modeled when more often the channel geometry was fixed, but the wall deformation and surface forces strongly influence the flow in confined gaps. A nonlinear lubrication framework is developed for a constricted compliant microchannel, coupling with the Helmholtz–Smoluchowski slip, electric-field focusing, Kirchhoff–Love wall bending, and DLVO disjoining pressure. It is identified that the stiff-wall, compliance-limited, and small-gap saturation regimes provided the scaling laws which relates the throughput analysis and deformation to curvature, wall stiffness, surface conduction, and intermolecular forces.

Electric field–driven droplet generation provides an active strategy for overcoming the limited controllability of conventional passive microfluidic methods; however, the mechanisms governing mode transitions under different combinations of electrical properties remain unclear. Here, we develop a coupled lattice Boltzmann–finite difference numerical framework to investigate electrohydrodynamic droplet formation in T-shaped microchannels under varying electric field strengths, permittivity ratios and conductivity ratios. We identify four droplet generation modes and reveal their transition mechanisms by analyzing interfacial charge distributions and electric-field forces.

This study investigates the diffusiophoresis of charged rigid colloids in yield-stress viscoplastic fluids using fully coupled electrokinetic simulations supplemented by thin-double-layer analysis, and demonstrates new avenues for manipulating particles in complex viscoplastic media. The results show that shear-thinning rheology enhances particle velocity significantly, whereas yield stress suppresses particle mobility and can even induce stalling. In shear-thinning fluids, a reversal of diffusiophoretic motion is observed at lower values of the flow consistency index, which is suppressed when diffusion-dominated transport is amplified for multivalent electrolytes or at higher yield stresses.

This study investigates experimentally the three-dimensional settling process of centimeter-sized spherical particles in still water using Particle Imaging Velocimetry (PIV) and Convergent Binocular Vision (CBV). When particles are released side by side, the number of particles significantly influences the settling process. Two particles settle synchronously almost in mirror-image, with random deflection largely suppressed, called the mutual support phenomenon (MSP). With more particles, the outermost two exhibit MSP, but other particles may fall like single particles. Observations of multiple particles with sophisticated instruments can reveal mechanisms of complex settling processes.

When flowing, elongated particles may exhibit a strong inhibition of their angular motion compared with spherical grain. We use discrete element simulations to investigate the angular dynamics of elongated particles in dense, confined shear flows. We show that this inhibition does not originate from single isolated mechanisms, but is governed by the degree of collective alignment induced by shear. We propose a simple scaling law relating the average angular velocity to the local shear rate. This scaling collapses data obtained for different particle properties and flow patterns, unifies spherical and elongated particles, and remains valid across two additional flow configurations.

Particle-induced viscous fingering (PIVF) occurs when a non-colloidal suspension displaces air inside a Hele-Shaw cell, which leads to the formation of particle clusters, or “plumes” at the advancing interface. Despite extensive studies in the last decade, the coupling between plumes and interfacial deformations remains unexamined. In this paper, we address this coupling by deriving scaling laws that connect the interplay between capillarity, local particle concentrations, and interfacial speed. We also uncover new regimes of PIVF that are unique to rectilinear geometry, in which particle plumes interact and coalesce, resulting in enhanced mixing inside the suspension.

Dynamic Taylor-based gradient models are derived forsubgrid turbulent heat flux and drift temperature components which arise in filtered heat transfer two-fluid model for turbulent gas-particle flows. Among them, the dynamic model coefficient based on optimal estimator procedure P${}^{Opt}$, improves the predictive accuracy of actual turbulent heat flux P${}^A$, in comparison to the conventional dynamic Smagorinsky-type approach P${}^S$, and the most common turbulent diffusivity linear gradient model P${}^G$

Particle-shape symmetry determines the form of inertial hydrodynamic forces and torques acting on particles settling in a quiescent fluid. Exploiting these symmetries provides a systematic way of analyzing how particle shape influences unsteady settling dynamics, by classifying particles according to their shape-symmetry groups. Our results help to understand the connection between particle geometry and the transient dynamics observed in settling experiments with particles of different shapes.

We propose a continuum two-dimensional model for cohesive granular flows down inclines. Using the Contact Dynamics method, we explore the parameter space of inclination angle and adhesion strength for which steady uniform flows develop. We then compare free-surface velocity and plug thickness with the model. We find that, at moderate inertial numbers $I$, the flow rheology can be described by a linear $\mu (I)$ friction law supplemented by a macroscopic cohesive stress. The independence of friction and adhesion is confirmed within the investigated parameter range, and the macroscopic cohesive stress is found to scale linearly with local contact adhesion, in agreement with Rumpf’s prediction.

The evaporation dynamics of a stretched spray lamellae is a paradigm for dense sprays evaporation. We consider lamellae made of densely packed micron-sized droplets of liquids with different volatilities, initially in equilibrium with their vapor. We confirm that the lifetime of an individual droplet is much larger than expected from the usual d-squared law for isolated droplets evaporating in a quiescent environment. By analogy with mixing times of scalars, we show that the boundary between the spray and the diluting environment is controlled by the dynamics of its saturating vapor concentration field, explaining the substantial evaporation delay despite the liquid’s division into fine droplets.

Oil–water emulsions exhibit viscosity contrasts that can significantly influence scalar transport and mixing. Using phase-field-based direct numerical simulations, we investigate the role of viscosity on the transient evolution of a passive scalar (temperature), initially confined in the dispersed phase and subsequently transferred to the carrier phase, in two opposite configurations: water-in-oli and oil-in-water emulsions. Despite fundamentally different local mixing dynamics in oil and water, reversing the continuous and dispersed phases redistributes these mixing mechanisms, preserving similar global heat-transfer rates and thermal transient in the two systems.

This study follows the interplay between velocity structures and concentration structures to explain the pattern of pollution behind a vehicle. Measurements of concentration, along with PIV measurements, show the effects of vehicle and wake topologies on pollutant dispersion.

Turbulence accelerates droplet growth in warm clouds, but reliable collision-kernel models remain elusive; and the effect of polydispersity beyond gravitational settling is often not accounted for. We provide a comprehensive map of the bidisperse collision kernel across St ∈ [002_2] and demonstrate that current models systematically overpredict cross-species clustering. We propose a compact parameterization that captures polydisperse collisions across Reynolds numbers, and show that droplet growth is markedly accelerated in highly dissipative parcels—supporting turbulent intermittency as a viable pathway past the warm-rain bottleneck.

Despite its geometric symmetry, flow past a highly confined cylinder is known to develop an asymmetric wake. This motivates an examination of the conditions under which this asymmetry is lost. The present results indicate that upstream turbulence can suppress wake bias and restore global symmetry. Turbulence induces early breakdown of the cylinder shear layers immediately after separation, disrupting their coupling with the wall shear layers that would otherwise sustain the asymmetric wake. These results further suggest that any mechanism capable of triggering early breakdown of the cylinder shear layers may likewise promote recovery of global symmetry.

Turbulent separation bubbles are known to exhibit low-frequency “breathing” but its origin remains unclear. This work shows that the dominant long-time dynamics can be captured by a nonlinear Langevin model fitted to Proper Orthogonal Decomposition amplitudes from time-resolved Particle Image Velocimetry. The results reveal bimodal, noise-driven switching between preferred separation states, providing a probabilistic dynamical-systems interpretation of the low-frequency unsteadiness.

Blood flow in the human heart is far from a smooth stream: it is a rapidly changing, intermittent motion shaped by moving walls, valves, and pulsatile forcing. By following Lagrangian tracers through a patient-specific simulation of the left heart, this study reveals where and when turbulent fluctuations become most intense. The results show that Lagrangian statistics can expose chamber-specific flow signatures and detect the enhanced intermittency produced by a stiffened aortic valve, opening a route toward sharper assessment of pathological cardiac flows.

Turbulence subjected to background rotation underlies many geophysical and engineering flows, yet its anisotropic development away from the rotation axis remains poorly constrained experimentally. This laboratory study examines nearly isotropic turbulence under controlled off-axis rotation using high-resolution PIV, revealing how rotation induces scale-dependent anisotropy in directional velocity spectra. The onset of spectral anisotropy follows a simple scaling with the inverse turbulent Rossby number, directly linking large-scale rotation to small-scale energy redistribution. These results offer experimentally grounded constraints for modeling rotating turbulence in non-inertial frames.

Two-equation RANS models often label (k) as turbulent kinetic energy, yet their (k) represents only the energy of Reynolds-stress-producing active motions in the logarithmic layer. This leaves the energy of inactive motions unresolved, despite its importance for normal stresses, curvature effects, wakes, and particle transport. We derive a transport framework for inactive-motion energy and show that its predicted scaling agrees with channel and boundary-layer DNS data.

We generalize the derivation of the velocity circulation area rule, initially proposed in the inertial range and stating that circulation statistics do not depend on specific loop shapes, to ranges with forcing and dissipation. With a newly proposed necessary condition, we show that the area rule cannot hold in the classic inertial range. Even so, in two-dimensional instability-driven turbulence, the variance-normalized circulation probability density function shows a weaker dependence on loop shape, suggesting that the normalized circulation statistics are potential measures of geometry-related turbulence invariances.

As they settle through turbulent clouds, elongated ice crystals, which form at low enough temperature, are affected by the turbulent motion of air. Such crystals, which are typically smaller than the Kolmogorov length scale of the flow, tend to align perpendicular to gravity, and to a lesser extent, parallel to vorticity. Turbulence is shown to increase the settling velocity of the crystals due to their inhomogeneous sampling of the flow.

We quantify how momentum-flux transport is organized across scales in the unstable atmospheric surface layer. Using multi-height SLTEST measurements, we show that cumulative cospectral ogives provide a compact description of scale allocation in the weak-cancellation regime. Increasing instability and relative height shift the dominant transport toward larger wavelengths, enhance outer-scale contributions, and strengthen scale-by-scale cancellation, while event-based diagnostics indicate a concurrent concentration of transport into fewer intermittent bursts.

Turbulent von Kármán flows in a cylinder with a height-to-diameter ratio of two show permanent strong inhomogeneity and anisotropy. Using helical-wave decomposition, the authors find an unusual -5/4 scaling law for the global energy spectrum of fluctuating velocity within an intermediate wave-number range while the structure function remains a classical 2/3 scaling within the corresponding scale range in physical space. Unlike homogeneous isotropic turbulence, energy transfer between scales remains nonzero in the scaling range, revealing how moving boundaries reshape the cascade of turbulent fluctuations

Flows over natural and engineered surfaces often involve roughness superimposed on larger topography, yet how this multiscale geometry modifies turbulence remains incompletely characterized. Using refractive-index-matched particle imaging velocimetry (PIV), this study shows that modest sinusoidal roughness on a wavy wall induces larger near-wall coherent motions and suppresses ejection events. This weakens local turbulence production and attenuates the separated shear layer in the adverse-pressure-gradient region, clarifying how multiscale surface geometry modulates momentum exchange over complex walls.

The space-time variations of wall-pressure fluctuations (p_w) provide key insights into the dynamics of turbulent boundary layers, yet accurate measurements of their large-scale frequency-wavenumber spectrum remain challenging at high friction Reynolds numbers (Re). Using a bespoke 63-microphone array designed to resolve the large-scale p_w field with minimal aliasing errors, we report novel measurements spanning across 1400 < Re < 5200. The results reveal that p_w scaled on the boundary-layer thickness is most strongly correlated with turbulence in the logarithmic region, identifying it as the dominant source of large-scale scale p_w relevant to turbulence sensing, modeling, and control.

Cloud supersaturation is modeled as a passive scalar with a phase-relaxation time under a uniform vertical gradient. Large eddy simulations with grid points of ${1024}^3$ confirm the theoretical prediction that one $-5/3$ spectrum by the phase relaxation and another by the turbulence cascade coexist at low and high wavenumbers in the inertial range, respectively. As the phase relaxation time becomes shorter the transition wavenumber between the two ranges shifts to higher wavenumbers, consistent with theory. Probability density function tails of the supersaturation at small-scales become longer than that of the velocity, stronger intermittency, as the phase relaxation time becomes longer.

We outline a workflow for examining statistically transient fluid flows, which eludes most standard modal analysis techniques. As a challenging example, we investigate the transient dynamics of a turbulent supersonic twin-rectangular jet flow. Forcing-induced perturbations are extracted using synchronized large-eddy simulations (LES) of the natural and forced jets, and a database is collected that captures an ensemble of realizations of these perturbations. From this ensemble, we study the time-varying mean flow deformation and perform space–time proper orthogonal decompositions.

We show that the spread of infinitesimal perturbations in a turbulent density-stratified fluid becomes slower with increasing degree of stratification. With a higher degree of stratification, the spatial growth of the uncertainty gets more and more compressed along the direction of stratification. Despite this, the temporal growth of perturbations follows the same universal behavior: an initial decay followed by an exponential growth, ultimately leading to saturation. The rate of growth of the perturbation, however, gets affected by stratification through the strain-mediated dynamics of the underlying velocity field, rather than through direct coupling with the density fluctuations.

Polymeric flows exhibit phenomena that sit at odds with our conventional understanding of turbulence. In this work, we show how a characteristic far-from-Kolmogorov self-similarity of polymeric turbulence owes its emergence to a phenomenon possible only in multiphase flows: polymers deplete the fluid energy cascade at a constant rate across scales. This constant loss of flux from fluid to polymers emerges as a second invariant of the turbulent, strongly coupled, fluid-polymer system (in addition to the total constant flux of energy from large to small scales). This invariant loss of flux dictates turbulence statistics in polymeric flows and gives it a distinct universal power-law behavior.

Active grids are widely used to generate turbulence, yet their near-grid region remains poorly understood. We show that global blockage is a key parameter governing near-grid turbulence statistics, driving qualitatively different behavior when grid configuration changes, in contrast to trends observed further downstream. We further reveal that forcing signatures persist strongly at large scales but decay toward dissipative scales, marking a transition from forcing-dominated to more universal turbulence.

Light and sound waves can be beamed at molecules or particulates to exert forces, induce motion, and control position. New experiments show that water waves can be used in much the same way at larger scales, and the findings open up new opportunities for action-at-a-distance manipulation. By controlling the shapes of suspended structures, the article shows that they may even be moved sideways or perpendicular to incoming waves. Further, by controlling the form of the wave field, objects can be stably held in place or “tweezed” at a desired location.

The present study extends existing investigations of waves generated by granular collapse into water from two-dimensional configurations to three-dimensional axisymmetric cases, revealing both similarities and fundamental differences between them. Wave-generation mechanisms are proposed, demonstrating that the competition between horizontal and vertical granular flow governs the transition between different regimes. A predictive framework for wave classification and maximum wave amplitude estimation has been provided.

This paper presents an analytical model for Mach reflection in axisymmetric internal supersonic flows that explicitly accounts for a center body. Using the curved shock theory and the method of curved shock characteristics, the model accurately predicts key flow features including the slip line shape and Mach disk size. A key advance is the identification of a negative pressure gradient behind the reflected shock that can form a sonic throat independently of the trailing-edge expansion fan, an effect achievable only for sufficiently small wedge angles where slip line deflection is mild.

The growth of wind-generated waves may depend on free-stream turbulence, a parameter that is generally neglected in existing models. Here, we investigate this effect experimentally using grid-generated turbulence blowing over a viscous fluid. Our results show that free-stream turbulence enhances the amplitude of three-dimensional wrinkles and lowers the critical wind velocity for the onset of regular two-dimensional waves, while the wrinkle–wave transition remains associated with an approximately constant friction velocity. A qualitative model explains why the observed decrease of the friction velocity with the fetch results in a non-monotonic variation of the wave amplitude.

We characterize the three-dimensional shape of an elastic, transparent sheet as it translates, rotates, and deforms - a key experimental challenge in the study of particle-laden flows – with a high-resolution, single-camera method. We scan the object nonintrusively to capture its illuminated surface and couple the space-time representation of its surface with a neural autoencoder to reconstruct the 3D shape of the object. This method enables the study of motion and deformation of objects with a wide range of surface geometries.