Feeding by marine invertebrate larvae depends critically on the low-Reynolds-number fluid mechanics of the feeding currents they generate. However, the relative importance of gravity-driven and drag-driven mechanisms in shaping these feeding currents has remained unresolved. By combining μPIV measurements with an analytical Stokes-flow model, this study demonstrates that feeding currents of eastern oyster (Crassostrea virginica) veligers are gravity-dominated despite their submillimeter size, and quantifies how excess weight, swimming kinematics, and ciliary propulsion together determine larval clearance rates and flow structure.

A mathematical model for the evolution of, and deposition from, a thin particle-laden droplet on a fully flooded porous substrate undergoing simultaneous evaporation and imbibition is formulated and analyzed. While the physical mechanisms driving evaporation and imbibition are rather different, it is found that there are several qualitative and quantitative similarities in the behavior of the droplet as it loses mass to its environment. Not only are these results of theoretical interest, but they are also relevant to a wide variety of practical applications that would benefit from an improved ability to predict and/or control the pattern of the final deposit left on the substrate.

Vortex cavitation in submerged jets is usually associated with turbulent continuous flows, yet an impulsively expanding bubble in a confined tube can trigger cavitation in a remarkably organized vortex ring. Combining experiments, theory, and simulations, we show that the intense initial acceleration of the jet generates an over-pressure contribution to vortex ring circulation, producing unusually high incipient cavitation numbers. This mechanism also explains why larger nozzles promote cavitation, revealing a size-scale effect in impulsive jets.

Lifting surfaces operating at aerodynamically low Reynolds numbers often have laminar separation bubbles (LSBs) whose characteristics can significantly affect performance. We investigate the effect of localized surface roughness, which might form due to manufacturing, local contamination, damage or icing, on LSBs. We find that the localized roughness eliminates downstream laminar separation and modifies the LSB topology and dynamics over a substantial spanwise region extending well beyond the roughness itself. The associated effect on aerodynamic performance is considerably greater than would be expected based solely on the relative spanwise extent of the localized roughness.

Extreme events in turbulent flows are rare, abrupt bursts in the system observable, posing significant challenges for prediction and control due to their nonlinearity and high dimensionality. Here, we present a predominantly data-driven framework for their suppression, combining dimensionality reduction through symmetry-aware autoencoders and data-driven clustering in the latent space of the former for the identification of precursors. A control law defined in this latent space substantially reduces the frequency and intensity of extreme events, by up to 99.4% in a canonical chaotic flow, demonstrating scalability to higher-Reynolds-number regimes and practical control limitations.

Liquid films flowing along fibers can exhibit distinct dripping and jetting regimes, yet the differences in bead-formation mechanisms and the transition between these regimes have received limited attention. By combining experiments with a theoretical model, we discuss the mechanisms governing bead formation in both regimes and introduce a method for identifying and predicting the transition range across different fiber-nozzle geometries. This work advances the fundamental understanding of bead formation and regime transitions in film flows on fibers.

Self-rewetting fluids that exhibit a quadratic dependence of surface tension with temperature result in thermocapillary flows that are markedly different from normal fluids. However, their behavior in the presence of an insoluble surfactant is not yet fully understood. We consider an inertialess surfactant-laden self-rewetting fluid film flowing down a heated cylinder under gravity, by deriving a reduced-order model under the lubrication approximation. A systematic linear stability analysis of our models indicates the stabilizing influence of surfactants at small wavenumbers, whereas conventional (anomalous) thermocapillarity is destabilizing (stabilizing) at mid-wavenumbers.

Gas transport in nanoporous media is strongly influenced by surface roughness, wettability, and molecular confinement, yet these effects are difficult to incorporate consistently into continuum-scale descriptions. We develop a molecular-based apparent permeability model that combines roughness corrections derived from molecular dynamics simulations with confinement and fluid–solid interaction effects. The model provides a systematic framework for disentangling these nanoscale mechanisms and predicting their combined influence on apparent permeability.

In granular films, where grains bridge the two interfaces of a soap film, the liquid pressure controls the transition from bursting to a jammed state. Even more, a single bursting event combines liquid- and solid-like mechanical responses. By identifying both an effective surface viscosity governing the early liquid-like regime and an internal dissipation controlling the late fracture dynamics, we provide a unified physical picture and highlight the differences between granular films and granular rafts. The concepts introduced here may prove relevant for a broad range of systems in which particles and interfaces interact, from particle-laden foams to biological or bio-inspired membranes.

Thermal diffusivity measurements in a sheared particle-fluid suspension are performed in a Taylor-Couette cell with outer cylinder rotation. The enhancement in diffusivity follows a power law with Peclet number with an exponent of 0.5 for Peclet numbers below 700 at all volume fractions studied (0.14, 0.22, 0.30 and 0.36). The data do not fit existing theory and are consistent with a model that assumes the formation of a particle-free fluid layer near the inner cylinder which causes deviation from an initially linear behavior at low particle Peclet numbers.

Fractal flocs occur in sediments, aerosols, and many particulate flows, yet their unsteady hydrodynamic inertia is often approximated using equivalent-sphere or free-draining models. We compute the added-mass and added-moment-of-inertia tensors of large ensembles of porous flocs over a range of sizes and fractal dimensions. The results reveal morphology-dependent anisotropy, systematic departures from simple approximations, and decreasing floc-to-floc variability with increasing size. We provide compact stochastic closures that can be used in large-scale simulations.

The drafting–kissing–tumbling (DKT) interaction of settling particles is a canonical problem in multiphase flow research, yet its behavior in oscillatory environments remains largely unexplored. Using particle-resolved direct numerical simulations, we investigate how horizontal oscillations modify binary particle interactions over a wide frequency and amplitude range. We show that oscillatory effects become significant only when oscillation-induced inertia exceeds viscous forces (Re${}_p$ > 1), leading to changes in contact duration and a preferential particle alignment perpendicular to the oscillation direction. Pressure field analysis reveals the underlying hydrodynamic mechanism.

Existing temporal super-resolution methods struggle to reconstruct three-dimensional turbulent flows across large time gaps, often losing coherent vortical structures and giving flow-specific performance. We introduce ResSE-LSTM, an attention-enhanced convolutional LSTM (long short-term memory) framework that recovers intermediate 3D velocity fields from two sparse snapshots and remains robust to noisy inputs. A Kolmogorov-scale temporal parameter, Π𝑡, unifies performance across Reynolds numbers. The model recovers Reynolds stresses and coherent structures up to Π𝑡 ≤ 4, versus Π𝑡 ≤ 0.8 for a CNN baseline, enabling reliable reconstruction from sparse simulations and measurements.

This study investigates the formation of the helical vortex rope in a Francis hydropower turbine by treating it as an unstable vortex breakdown mode in a simplified laminar flow. The vortex rope emerges through a supercritical Hopf bifurcation from an axisymmetric base flow in the draft tube. Without wall friction, a central recirculation zone develops, revealing subcritical solutions and hysteresis under partial-load conditions. The work describes the cyclic formation and collapse of the recirculation bubble as the helical vortex evolves. As flow approaches nominal load, the steady solution branch undergoes a transcritical bifurcation at finite Reynolds number.

This study introduces a novel approach for generating isolated vortex gusts in both computational and experimental settings. Utilizing a symmetric airfoil undergoing simultaneous heaving and pitching, this method delivers coherent vortices while minimizing persistent wake disruption downstream. The result is a customizable approach allowing precise, systematic control over vortex strength, orientation, and position.

Compared with a static liquid film, gas jet impingement on a flowing liquid metal film produces a shallower cavity and a strongly asymmetric profile through upstream liquid accumulation. Counter-current coupling upstream and co-current coupling downstream cause the wave-amplitude response to jet momentum to weaken upstream but strengthen downstream as the liquid Reynolds number increases. Under pulsating jets, an attenuation coefficient correlates wave amplitude with jet momentum and characterizes a pronounced spatial asymmetry in momentum transfer. These findings clarify how gas jets influence the liquid metal film flow and provide a reference for the design of liquid metal divertors.

Surface tension is frequently measured with the pendant drop method, while the ambient humidity is usually an afterthought. With carefully calibrated experiments and detailed numerical simulations, we show that evaporative cooling lowers the drop temperature by up to 9.5 K which in turn raises the measured surface tension by more than 1 mN/m. Evaporation-driven and Marangoni-induced flows additionally deform the drop, but only marginally. A passive humidity control removes these artifacts entirely and reveals the shallow minimum in the surface tension of aqueous 1,2-hexanediol mixtures.

What if we could learn not just which mode structures dominate a flow, but how they actually drive fluid-particle transport? This paper bridges Eulerian modal analysis and Lagrangian coherent structures by introducing modal-trajectory uncertainty, a sensitivity-based framework that reveals where specific modes influence particle trajectories and finite-time Lyapunov exponent (FTLE) structures. Across cylinder wakes, an oscillating-foil wake, and turbulent channel flow, the approach reveals interactions spanning vortex shedding, shear-layer instabilities, and large-scale turbulent motions.