We present a combined theoretical and numerical investigation of the inertial exit dynamics of a long horizontal circular cylinder vertically lifted out of a finite-size liquid bath at constant velocity. The various steps of the exit dynamics are studied in detail: from the formation of a bulge on the surface ahead of the cylinder to the coating of the cylinder by a liquid film while crossing the interface. We focus on inertial dynamics, a regime characteristic of large exit velocities, i.e. large Reynolds numbers ( $500 \lt \textit{Re} \lt 10\,000$ ) and negligible interfacial effects. The dynamics is investigated through two-dimensional computations of the Navier-Stokes equations using a finite element method with moving boundaries. We describe in detail the exit dynamics while emphasising the effect of various parameters on surface deformation and resistive force. We identify subtle effects and interplay, such as initial free-surface response after impulsive start-up, the important role of the lateral bounding of the reservoir, and the close relationship between wake size and surge amplitudes as revealed by comparing with free-slip cylinder simulations. All these aspects are shown to be crucial to accurately predict the coated film thickness and the exit force.

An antibubble is an object in which a liquid core is separated from a surrounding liquid by a thin spherical gas shell. Such structures can be generated when a droplet crosses a soap film with sufficient kinetic energy to become wrapped by the film, which then merges upon contact with a liquid bath. When droplets fall through multiple soap films, multilayer antibubbles can be generated. In this paper, the conditions required to successfully generate monolayer and multilayer packed droplets are studied in order to optimize the formation of monolayer and multilayer antibubbles. In particular, the geometrical factors and the composition of the liquid that makes up both the droplets and the soap films are discussed. The stability of antibubbles generated using this method is also investigated as a case study. The robust formation of monolayer and multilayer antibubbles is a key to open opportunities in drug delivery without the use of either oil or solid compounds. Moreover, this method allows for the production of monodisperse, millimetric, and multilayered antibubbles.

The motion of a water droplet on a single vertical sugar fiber is analyzed. The fiber is positioned vertically, with the droplet placed at its pending end. If the capillary force exceeds the weight of the droplet, the droplet remains suspended at the fiber's extremity. As water dissolves, the fiber eventually breaks. Subsequently, the droplet may fall down carrying a portion of the undissolved fiber or, more interestingly, the droplet may be propelled upwards, remaining attached to the fiber. The process can then restart. A phase diagram is constructed based on the droplet's volume and the fiber's diameter. A model has been built to assess the critical droplet volume for a given fiber diameter, above which the droplet falls. Below this volume, the droplet can move upwards along the fiber.

We investigate the vortical dynamics generated during the forced exit of a circular cylinder through a quiescent free surface. While previous work on exit flows has largely emphasized cavity collapse and force generation, the formation and evolution of the starting vortex beneath the body have received much less attention. Using highspeed particle image velocimetry at up to 2000 Hz, we isolate and track the primary vortex shed during exit. The body motion is driven by constant vertical acceleration from rest, such that the cylinder kinematics satisfy U2cyl = 2a dycyl, with dy cyl the displacement since release. This controlled protocol allows systematic variation of awhile keeping the maximum crossing velocity fixed. We characterize vortex trajectories, equivalent radius, peak vorticity, and circulation, and compare across accelerations. The results show that the circulation growth root collapses under the impulse-based scaling r/a (dy cyl)3, independent of the imposed acceleration. A consistent transition is observed as the vortex centroidapproaches the free surface, where its evolution is modified by surface interaction. The trajectories remain predominantly vertical with only weak lateral drift, robust across all accelerations. Taken together, these findings establish a systematic framework for water-exit vortex dynamics under constant acceleration and highlight scaling features that parallel the classical starting-vortex problem in entry flows.

Fluidised granular beds are used in a variety of industrial applications, such as heat exchangers, chemical reactors and energy storage systems. Fluidisation increases the interaction surface between the grains and the fluid, thus improving heat transfer. In this paper, an unresolved/semi-resolved FEM-DEM model is introduced to simulate immersed granular flows, incorporating heat transfer and vaporisation. As the fluid is modelled using a volume-averaged approach, constitutive laws are introduced to represent the momentum and heat transfer between the grains and the fluid. Based on the Colburn-Reynolds analogy, a Nusselt correlation is proposed to quantify the heat transfer of an assembly of grains within a fluid. The proposed law is validated by experimental measurements of heated granular beds taken from the literature. Heat transfer in a bubbling fluidised bed is studied as a numerical benchmark. The spontaneous digging of a droplet of water in a hot granular bed is investigated. When a droplet of water is placed on the surface of a hot granular bed, depending on the granular temperature, it can dig spontaneously into the bed. The main trends of the experiment, namely digging, local fluidisation and the formation of a chimney, are reproduced by the simplified two-dimensional numerical model. Heat transfer during the excavation process is investigated to highlight efficient transfer due to the local fluidisation. It is demonstrated that both injection fluidisation and local vaporisation fluidisation are correctly captured, as is heat transfer between the different phases.

A Leidenfrost drop made of inflammable liquid exhibits increased evaporation when inflamed. Contrary to the classical Leidenfrost framework, the evaporation from the top part cannot be neglected anymore. Herein, we report the evaporation dynamics of an inflamed drop for various wall temperatures. The combustion duration is found to be significantly longer in the Leidenfrost state than below the Leidenfrost transition. For large drops, we show that we can split the evaporation of inflamed Leidenfrost drops into two independent systems: the bottom and top parts. Assuming that the bottom contribution does not depend on the combustion, the top contribution can be extracted and analyzed, which is observed (i) to remain smaller than the bottom contribution and (ii) to be constant in the temperature range considered. This implies that the top evaporation rate is solely due to the intrinsic burning rate of the flammable liquid at saturation temperature.

We experimentally investigate the wake dynamics of a square cylinder rising through quiescent water over a range of Froude numbers (Fr). Time-resolved particle image velocimetry provides velocity and vorticity fields that enable pressure reconstruction and vortex characterization. Diagnostics based on swirl strength (λci), the Okubo–Weiss parameter (W), and a shear–vortex interaction measure (Λ) reveal that the wake is governed by a persistent pair of counter-rotating vortices rather than by periodic shedding. Circulation exhibits a two-regime dependence on Fr, with a sharp increase below Fr≈1 and saturation above this threshold, mirroring entrainment force scaling reported previously. While vortex area remains nearly constant, swirl strength and negative-W regions expand with Fr, indicating that entrainment enhancement arises from intensified rotation rather than an enlarged vortex footprint. These findings provide new physical insight into vortex-free-surface interactions and enrich the understanding of entrainment mechanisms in unsteady wakes, with implications for multiphase flows and the hydrodynamic design of naval and offshore structures.

Dripping fire, caused by flammable liquids falling onto solid surfaces, presents a significant challenge for fire hazard management due to its concealed and unpredictable nature. In this study, we investigate the evaporation and burning characteristics of dripping fire and ascertain that self -extinguishment can occur under specific drip masses and frequencies owing to heat transfer from the heated substrate to the droplet and thermocapillary motion of burning droplets. By controlling these drip parameters, we observe three distinct burning regimes: non -extinguishing, self -extinguishing, and non -igniting; furthermore, we confirm that their critical drip masses and frequencies follow a power function with an exponent of 3/2. We develop an evaporation model to predict the occurrence of the self -extinguishing regime, which aligns well with experimental results. Additionally, by designing substrates with diverse surface structures and thermal properties to manipulate evaporation dynamics and motion behavior of burning droplets, it is possible to significantly reduce the burning duration of dripping fires from over 120 s to under 20 s. Overall, this finding offers a novel approach to mitigating fire hazards related to flammable drips in various settings such as buildings and industrial environments.

Experimental investigations of the exit dynamics of a horizontal cylindrical object were performed in water and silicone oil (50 cSt). The fully immersed cylinder was initially at rest in a still fluid tank before being pushed (or pulled according to the measurement procedure) upwards at a constant velocity. Firstly, we demonstrate that these conditions are better satisfied for a large aspect ratio cylinder equipped with vertical side plates. Secondly, the influence of the initial depth on the liquid entrained and the wake generated by the cylinder is discussed. The deformation of the bath is found to be independent of the starting depth when the starting depth is larger than 6 times the cylinder diameter. In the present case, this criterion reflects also the finite acceleration of the cylinder to reach the determined constant exit velocity. Measurements in a range of exit speeds between 0.1 and 1 m/s indicate that the thickness of the liquid above the cylinder, when the cylinder starts crossing the interface, increases with the speed according to a logarithmic law of the Froude number. During the subsequent drainage, the evolution of the coated liquid thickness is found to first decrease exponentially with time just after the crossing of the interface. At later times, a change of regime occurs and the drainage follows the inverse of the square root of time irrespective of the crossing speed. Finally, the force necessary to maintain a constant exit speed during the motion of the cylinder inside and outside the bath is analyzed. This global measurement of the entrained liquid confirms the square root scaling of the thinning with time during the drainage process.

Antibubbles are ephemeral objects composed of a liquid core encapsulated by a thin gas shell immersed in a liquid bulk. The gas shell thickness evolves in time, driven by two contributions: gravitational drainage and gas-liquid mass transfer. The low density contrast between the antibubble and the bulk, as well as its weak deformability constitute advantages that are used to measure the mass transfer coefficient (MTC) in a socalled antibubble column, in a time-resolved fashion. Shells made with pure air give low data reproducibility. Consequently, perfluorohexane, a low-solubility gas, was mixed to air to enforce gas desorption from the bulk and obtain reliable data. MTC obtained with various surfactants and concentrations are found to deviate from the Fr & ouml;ssling correlation built for fully rigid interfaces: higher MTC are consistent with partially rigid interfaces due to a partial coverage of surfactants along a so-called spherical cap, while lower MTC are consistent with an additional resistance to the transfer of mass due to the presence of surfactants forming a monolayer at high concentration. Finally, the advantages in terms of control and compactness of an antibubble column as compared to a bubble column for liquid-gas mass transfer are demonstrated. Specifically, an antibubble is shown to transfer dozens of times more mass than a bubble that would initially carry the same amount of gas. Antibubbles are therefore shown to provide a new, time-resolved, way to measure MTC, as well as promising route to enhance liquid-gas transfers in multiphase reactors.

In this paper, we experimentally investigate the exit dynamics of a square cylinder, that is initially fully immersed in a water tank and that crosses the interface perpendicularly to its symmetry axis. The cylinder moves upwards at a constant velocity in the vertical direction till the cylinder exits out of the water into the air. The experiments were performed at different traveling speeds. The images of the cylinder crossing the interface were taken using a high-speed camera. The images were used to track the interface deformation when the cylinder approaches and crosses the interface. On top of these measurements, the force required to move the cylinder was simultaneously measured to estimate the drag force during the travel in the tank, the force of entrainment, and the force of crossing over the interface. Particle image velocimetry was performed to visualize the flow. Correlations between the different measurements are inspected.

This article experimentally investigates the exit dynamics of two different spheres i.e. a smooth sphere and a sphere with dimples at a constant speed. Employing high-speed experimental observations, the study investigates the key characteristic lengths and hydrodynamic forces between the sphere's surface and water. The experiments were performed at different traveling speeds (or Froude numbers). The results shed light on the drag force coefficient, entrainment force coefficient, and cross-over force coefficient. In this paper, we have shown that the surface dimples not only affect the drag force but also the entrainment force. However, the cross-over force coefficient remains the same.

In various types of many-particle systems, bidispersity is frequently used to avoid spontaneous ordering in particle configuration. In this study, the relation between bidispersity and disorder degree of particle configuration is investigated. By using magnetic dipole-dipole interaction, magnet particles are dispersed in a two-dimensional cell without physical contact between them. In this magnetic system, bidispersity is introduced by mixing large and small magnets. Then, the particle system is compressed to produce a uniform particle configuration. The compressed particle configuration is analyzed by using Voronoi tessellation for evaluating the disorder degree which strongly depends on bidispersity. Specifically, standard deviation and skewness of the Voronoi cell area distribution are measured. As a result, we find that the peak of standard deviation is observed when the numbers of large and small particles are almost identical. Although the skewness shows non-monotonic behavior, zero skewness state (symmetric distribution) can be achieved when the numbers of large and small particles are identical. In this ideally random (disordered) state, the ratio between pentagonal, hexagonal, and heptagonal Voronoi cells become roughly identical, while hexagons are dominant in monodisperse (ordered) condition. The relation between Voronoi cell analysis and the global bond orientational order parameter is also discussed.

Antibubbles are ephemeral objects composed of a liquid drop encapsulated by a thin gas shell immersed in a liquid medium. When the drop is made of a volatile liquid and the medium is superheated, the gas shell inflates at a rate governed by the evaporation flux from the drop. This thermal process represents an alternate strategy for delaying the antibubble collapse. We model the dynamics of such "thermal" antibubbles by incorporating to the film drainage equation the heat-transfer-limited evaporation of the drop, which nourishes the gas shell with vapor, as for Leidenfrost drops. We demonstrate that the inflation of the gas shell is drastically inhibited by the thermalization of the initially colder drop. Because of this thermalization effect, smaller drops evaporate much faster than larger ones.

The deformation of hemispherical sessile bubbles made of ferrofluid soap under vertical uniform magnetic fields was studied using Helmholtz coils. The deformation and the shape of the bubbles were monitored according to the amplitude of the magnetic field, the initial volume of the bubbles and the ferrofluid volume used to create them. The meniscus was found to bear most of the deformation, reshaping into a cylinder, with the remainder of the bubble forming a spherical cap, mainly adapting to the meniscus transformation. The growth of the meniscus height was rationalised using a simple model. More precisely, the meniscus shape depends on the competition between capillary, gravity and magnetic effects. These three ingredients can be rewritten to highlight two characteristic lengths of the system: the capillary and the magnetic lengths. Depending on the magnetic field intensity, the shape of the meniscus is described by one of the two lengths, thus revealing the existence of two distinct regimes.

An antibubble is an uncommon fluid object with a unique structure: a liquid globule is wrapped by a thin air film, with the whole being immersed in a liquid bath. In short, the antibubble is the opposite of a soap bubble. The antibubble has been regarded as a promising candidate for various industrial applications since two components can be separated only by an air layer before mixing. However, the use of the antibubble is limited by the short lifetime (approximate to 1 min) and the broad distribution of the lifetimes. We demonstrate a simple and efficient method to extend the lifetime of the antibubbles. The proposed system consists of a liquid surface covered by a layer of bubbles under which antibubbles are generated. The liquid is then vertically shaken. Above a given acceleration threshold that depends on the frequency, the lifetime of the antibubbles is significantly increased. Under vibrations, antibubbles were kept alive up to 13 h. As soon as the vibration is stopped, the antibubble collapses immediately. The antibubble popping can therefore be programmed A model based on the dynamical air drainage in the air shell of the antibubble is proposed to account for these observations.

The systematic use of plant protection products is now being called into question with the growing awareness of the risks they can represent for the environment and human health. The application of precision agriculture technologies helps to improve agricultural production but also to rationalize input costs and improve ecological footprints. Here we present a study on fungicide application efficiency and its impact on the grass quality of a golf course green using the free open-source image analysis software FIJI (Image J) to analyze ground RGB (high-resolution digital cameras) and multispectral aerial imagery in combination with experimental data of spray pressure and hydraulic slot nozzle size of a boom sprayer machine. The multivariate regression model best explained variance in the normalized green-red difference index (NGRDI) as a relevant indicator of healthy turfgrass fields from the aerial, ground, and machine data set.

In this article, we study the division of a non-laminar Savart sheet into individual jets by mean of local disturbances. We paint a precise portrait of a free non-laminar Savart sheet formed by the vertical impact of a jet on a horizontal disk, its evolution in the air and its break up. We then generate local disturbances, outside of the disk circumference, triggered by N radial triangular prisms placed directly in the non-laminar sheet. We show that, under given flow conditions and geometrical parameters for the triangular prisms, the sheet splits into individual jets. Depending on the incoming flow rate Q and on the geometry of the prism, the number of jets n can be either stable (and equal to N jets) or variable due to elastic coalescing of neighboring jets. Phase diagrams (Q, n) are obtained from experimental measurements for different geometrical parameters of triangular prisms. A semi-empirical model, which explains the generation of individual jets, is established. Finally, we characterize the droplets emitted from the non-laminar Savart sheet and from the jets in terms of diameters.

African agriculture is adversely impacted by arable soil compaction, the degree of which is affected by the speed at which the tractor is maneuvered on the fields, which affects the degree of soil compaction. However, there is no reliable, existing mathematical correlation between the extent of compaction on the one hand, and the tractor speed/s and soil moisture levels on the other. This paper bridges this gap in knowledge by resorting to the artificial neural networks (ANNs) method to predict the effects of tractor speed and soil moisture on the state of soil compaction. The models were 'trained' with penetration resistance (CPR) and bulk density test data obtained from field measurements. The resulting correlation coefficient (R = 0.9) showed good compliance of the prediction made with the ANN models with on-field data. It follows, thereby, that the model developed by the authors in this study can be effectively used for predicting the effects of speed, soil density, and moisture content on compaction of alluvial, poorly developed soil with much greater precision, thereby providing guidance to farmers around the world.