Formation Of Liquid Jet Research Articles

Cavitation and jetting from shock wave refocusing near convex liquid surfaces

We study the physical mechanisms behind the ejection of a liquid jet from a curved free surface, specifically a free-falling water drop. The jet is produced after a spherical shock wave emitted from a micro-explosion created by a focused laser pulse is refocused on the opposite side of its source. The analysis of high-speed videos of the liquid jet formation revealed that it originates from a larger, prolate cavitation bubble created by the strong tension produced after the reflection of the original wave on the air–liquid interface. The shock wave propagation and jet formation are modeled separately with finite volume simulations in OpenFOAM. Initially we study the pressure evolution inside the drop by comparing the numerical simulations with the distribution of bubbles nucleated after the passage of the negative pressure wave. The jet formation dynamics is explained by comparing the experiments with numerical results. The jet velocity is higher if the laser focus is closer to the drop surface.

On the interaction of two cavitation bubbles produced at different times: A jet from the primary bubble

The liquid jet formation upon the collapse of two interacting cavitation bubbles is a physics-rich complex problem, which has possible implications such as the membrane sonoporation. In this paper, we employed both experiment and numerical simulations to study the jet behavior in a bubble, which is affected by another one introduced at various time delays. We provided the regime diagram, which shows the transition of the jet direction as a function of time delay and distance between bubbles. The maximum velocity of the jet in the primary bubble was investigated. The highest velocity was achieved when the primary bubble split into two parts upon collapse. It was found that a high curvature on the rim of the collapsing primary bubble causes the lateral pinch-off, leading to the formation of a fast and thin vertical jet approaching the secondary bubble. The results would help design an effective sonoporation system. The physics depicted in this manuscript might also contribute to the deeper understanding of the jet in a bubble interacting with not only another bubble but also other boundaries.

Numerical investigation of acoustic cavitation and viscoelastic tissue deformation

Acoustic cavitation and tissue deformation are studied by modifying a level-set method for compressible two-phase flows to consider viscoelastic tissue deformation. The numerical simulations performed using different shear moduli and bubble-tissue distances demonstrate various interactions between bubble and viscoelastic tissue, including inverted cone-shape bubbles, bubble migration, liquid jet formation, compressive and expansive tissue deformation, and tissue perforation. The bubble is observed to grow larger with increasing tissue bulk modulus and density. The maximum tissue deformation generally increases with decreasing initial bubble-tissue distance and with increasing tissue bulk modulus and density. The tissue shear modulus conditions that maximize tissue deformation are in the range of 1–10 MPa, unless the tissue density is very large.

Formation of volatile liquid jets in a rarefied medium

The external signs and conditions for the occurrence of sudden changes in the direction of ethanol micro-jets during vertical, from top to bottom, outflow from small-diameter capillaries into a rarefied medium (vacuum) are considered. A brief description of the equipment used, the organization of liquid preparation for the experiment, and the control of parameters are given. With the help of photo and video equipment, sudden transitions from dark areas of the jet to light ones and vice versa, stratification of the liquid jet into two, three or more fan streams, i.e. bifurcation. It is shown that with a decrease in the diameter of the capillary opening, the jet outflow is more stable, and the flow can retain its shape for a relatively long period of time. The process established by other researchers of the flow of liquid drops up the capillary has been confirmed. The reliability of the obtained results was verified by comparison with the known data by organizing the outflow from the same capillaries into the atmosphere.

Numerical investigation of two-microbubble collapse and cell deformation in an ultrasonic field

Two-microbubble collapse near a spherical cell in an ultrasonic field is numerically analyzed by extending a level-set method for compressible multiphase flows with bubble and cell multiple interfaces. Computations performed with different bubble-bubble distances and size ratios demonstrate various bubble-bubble interactions, such as bubble coalescence, bubble repulsion and attraction, jet penetration into the bubble, and jet collision. The interactions between collapsing bubbles are found to produce strong liquid jet formation and result in significant cell deformation compared to single-bubble collapse. The optimal bubble-bubble distance and size ratio for cell deformation are presented via contour maps based on extensive computations. The influences of the ultrasonic amplitude and frequency on cell deformation are further investigated.

Thermal nonequilibrium and mechanical forces induced breakup and droplet formation of superheated liquid jets under depressurized release

Superheated liquid jets disintegrate into numerous droplets when released into the ambient with lower saturated pressure, driven by thermal nonequilibrium induced flashing and the accompanying mechanical forces. Such a phenomenon facilitates fuel atomization in energy utilization while posing a serious threat during accidental releases. In this work, the breakup and droplet formation of superheated liquid jets under depressurized releases were investigated with an experimental 20 L tank. A high-speed camera was utilized to characterize breakup behaviors. The interaction between thermodynamic and mechanical effects during depressurization was discussed based on linear stability analysis and bubble dynamics. Furthermore, the quantitative relationship between the two driving effects under different conditions was established using dimensionless and multiple regression analyses. Results show that the thermodynamic effect increases with the decreased mechanical effect during depressurization because of the increased energy of bubble burst, regardless of the external or internal flashing regime. Non-flashing, partially flashing, and fully flashing breakup modes are identified. The dimensionless and multiple regression analyses show that in addition to thermodynamic (Ja, ρv/ρl, Rp, and ηp) and mechanical (Wev and Oh) effects, the inhibition induced by the cooling effect (Pr and Ec) should not be overlooked. The quantitative expression among them agrees well with experimental data with R2 = 0.976.

Jetting and migration of a laser-induced cavitation bubble in a rectangular channel

The jetting behaviour and migratory characteristics of a laser-induced cavitation bubble in a rectangular channel are investigated both experimentally and numerically, for various combinations of the geometric and physical parameters of the system. High-speed photography is used to visualize the temporal development of the bubble shape, the formation of liquid jets during bubble collapse, and the bubble displacement in contact with the sidewalls of the channel during two oscillation cycles of the bubble. The bubble profiles, pressure contours and velocity vectors ambient to the bubble are obtained through numerical simulation results by using an Eulerian finite element method with a compressible liquid impact model. The jetting behaviour of the bubble varies between single jet formation and the formation of three liquid jets directed towards each wall of the channel. The numerical calculations indicate that the liquid jets directed towards the sidewalls of the channel reach maximum velocities of 100 m s−1while the peak velocity of the liquid jet directed towards the channel endwall is about 55 m s−1. A small bubble generated close to a sidewall of the channel develops only a single inclined jet during collapse. Such jets can reach velocities of up to 110 m s−1. A bubble displacement in contact with the sidewalls of the channels of 350 μm was observed during the first two oscillation cycles for a bubble with a maximum diameter slightly smaller than the height of the channel. The results of our investigations are compared to previous results obtained in similar configurations.

Bubble dynamics near a locally curved region of a plane rigid wall

The dynamics of a bubble near a local axisymmetric convexity or concavity, cosine-like in the axial section, on a plane rigid wall is studied under conditions of formation of a cumulative liquid jet directed to the wall. The study is performed by the boundary element method. Our main attention is focused on the bubble collapse characteristics at the moment tc when the jet impacts on the bubble surface part near the wall, namely, on the jet tip velocity and radius, the internal bubble pressure, the distance between the bubble and the uneven region of the wall, and so on. These characteristics are of interest since they, to a large extent, determine the destructive potential of cavitation. The dependences of these characteristics on the radius of the non-plane region of the wall, the depth of the concave region, the height of the convex region, and the local character of the wall unevenness have been investigated. To estimate the effect of the local character of the wall unevenness, the cases of completely concave and convex walls in the form of blunt conical surfaces are used for comparison. It has been found, in particular, that with changing radius of the convex region of the wall, the bubble shape at the moment tc varies significantly: the shape diversity includes the profiles with a gas microcavity in front of the impacting jet tip, an emerging second oppositely directed jet, and a relatively large area of the jet tip impact at its beginning.

Laser bioprinting without donor plate

A promising laser bioprinting technology based on the effect of laser-induced direct transfer is rapidly developing and is already actively used in biotechnology and medicine today. Typically, such technologies use donor plates with an absorbent coating, from which gel microdroplets with living cells and microorganisms are transferred to an acceptor substrate under the action of a laser pulse. This article proposes a new bioprinting technology that makes it possible to transfer microdroplet not only without an absorbing coating, but also without the donor plate itself. The essence of this method is that the transfer to the surface of the acceptor is carried out by a series of nanosecond pulse with a wavelength of 3 μm directly from the surface of a liquid with microorganisms. The mechanism of a liquid jet and microdroplets formation upon absorption of a laser pulse in a thin surface liquid layer is discussed in detail. It has been shown that microorganisms transferred using the new bioprinting technology are viable and can be successfully cultivated on a dense nutrient medium.

Evolution of jets during drop impact on a deep liquid pool

The impact of a liquid drop on a liquid pool has been widely investigated. The transition regimes between coalescence and splashing of drops include jet formation with single or multiple secondary drops. One of the main features in this regime is the formation of a central liquid jet followed by breakup of the jet in the form of drops. Earlier studies have shown that the diameter of the secondary drop lies between 0.58 and 0.94 times the diameter of the impacting drop. We perform investigations based on a coupled level-set and volume-of-fluid method to elucidate the earlier observations. The investigations reveal the creation of a variety of secondary drops depending on the impact conditions. The present study also reveals that secondary drops larger than the initial drop can be obtained at higher impact velocities. We identify the importance of cavity shapes on the formation of jets and the pertaining parameters that are responsible for drop ejection.

Bubble collapse and jet formation inside a liquid film

The cavitation of a hemispherical bubble nucleated inside a liquid film of microscale thickness and the subsequent formation of liquid jets are investigated numerically, using the compressible volume of fluid method, in particular, in the context of laser-induced forward transfer (LIFT). Because of the presence of both a solid wall and a free surface, the dynamics of the bubble differ notably from those near a solid wall alone or a free surface alone. When the liquid film is sufficiently thin, the shape of the expanded bubble becomes narrow along the axial direction, forging a stretched cone with a spike. The interface of the bubble near the spike opposite to the solid wall contracts much earlier than the other parts, leading to the separation of the spike. As a result of this separation, the collapse of the bubble is stronger, and the outward jet and inward jet along the axial direction are sharper and faster. However, as the film thickness increases, the tip separation of the bubble becomes weaker, and both outward and inward liquid jets become thicker and slower. In addition, an increase in liquid viscosity changes the bubble shape from an axially stretched cone shape to a round shape because of enhanced viscous force along the radial direction inside the thin film, which eventually results in disappearance of the inward jet. The fundamental insights elucidated in this work can serve as a quantitative design guideline for the LIFT.

Accurate hybrid AUSMD type flux algorithm with generalized discontinuity sharpening reconstruction for two-fluid modeling

This paper presents a single-pressure-field two-fluid model with finite-volume discretization to solve the equations of motion of compressible multiphase flows. To capture the discontinuities caused by shock waves and fluid interfaces, we propose a generalized discontinuity sharpening technique that combines the conventional monotonic upstream scheme for conservation law (MUSCL) and tangent of hyperbola interface capturing (THINC) schemes. In addition, a slope ratio-weighted parameter, ζ, is used to control the proportion of values reconstructed by MUSCL and THINC, and we show that the present method can retain sharp interfaces when the value of the parameter β in the THINC scheme is set ranging from 1.6 to 3.0. Fluxes across various interfaces are evaluated using a hybrid AUSMD-type flux algorithm, where the mass flux and pressure induced on the cell faces are calculated using an approximate Riemann solver. The accuracy and robustness of the proposed method are validated by solving a series of one- and two-dimensional single-phase flows. Furthermore, complex wave patterns arising from two-dimensional shock bubble/water-column interactions are examined, which indicate that compared with the existing schemes applied to two-fluid modeling, the proposed scheme significantly sharpens the interfaces and captures more details of the flow features. Finally, simulations of a three-dimensional example of the liquid jet crossflow are conducted. The proposed scheme shows more details of the fluid interface, including the interfacial instabilities on the windward side of the liquid jet and droplet formation due to the breakup phenomenon in the downstream of the crossflow, than the existing schemes.

Effect of liquid elasticity on the behaviour of high-speed focused jets

We investigate the effect of highly contrasting non-Newtonian liquid properties on the formation of liquid jets with a focused shape. By using two nozzle-free ejection techniques, mechanically impact- and laser-induced, fast jets of a highly elastic (sodium polyacrylate) and weakly elastic (xanthan-gum) diluted polymer solutions are generated. A unique high-speed effect is encountered at the jet ejection onset of the highly elastic solution. Its jet-tip speed is on average 1.4 times faster in comparison to a Newtonian (glycerin/water) and the weakly elastic liquids. We explain this effect occurring as a result of the high viscoelasticity of the sodium polyacrylate solution. Additionally, a ‘bungee jumper’ jet behaviour (Morrison and Harlen in Rheol Acta 49(6):619–632, 2010) is observed in a regime of high speed (10<V_j<40 m/s) and high viscosity (mu >20 mPa s) not previously examined. We additionally characterise the viscoelastic non-breakup jet limit using the Bazilevskii et al. (Fluid Dyn 40(3):376–392, 2005) ejection criterion. Herein, the extensional rheological parameters are measured implementing a novel DoS-CaBER technique (Dinic et al. in Lab Chip 17(3):460–473, 2017). Our findings may influence results of inkjet printing technologies and recent nozzle-free ejection systems for ejecting liquids with non-Newtonian properties.Graphical abstract

Liquid jet-based broadband terahertz radiation source

The features of a liquid jet-based broadband terahertz (THz) generator that includes an optical part and system for a liquid jet formation are described. This system is based on the trapezium-shaped slit-type nozzle, the output of which is limited by two parallel blades. The applications of this generator for studying the optical-to-THz conversion efficiency for various liquids and THz energy temperature dependence are demonstrated. A trend for a decrease in the optical-to-THz conversion efficiency when using high-temperature water is revealed. This trend is interpreted through the increase in the THz wave absorption of the water jet. This system allows to achieve the optical-to-THz conversion efficiency up to 0.1% in the case of α-pinene double-pulse excitation.

Research of mechanisms of interaction of melt and coolant by means of small-sized experiments with solid and liquid metal samples

Several basic fragmentation hypotheses described in the literature for the case of fine-scale spontaneous vapor explosion, when single hot drops are falling in the coolant, are analyzed. It is shown that all of them, depending on the experimental conditions, describe the real physical phenomena. It is highlighted, that the process of fragmentation during the spontaneous vapor explosion is directly connected to the regime of the film boiling collapse of the underheated liquid, which is still underexplored. The experiments on the liquid drops fragmentation are complemented by those with surface boiling at the solid metal samples of semi-spherical form. The connection between the vapor explosion of water and the increase of the surface wettability is confirmed. The video material, indicating the possibility of formation of liquid jets that strike the hot surface during the collapse of the vapor shell, is obtained. The time interval (duration of the contact) between the first contact of the coolant with the hot surface and the explosion boiling of the liquid is experimentally determined. The dependence of the contact duration on the temperature of the overheated wall is determined and its comparison with the theoretical estimations is provided.

The ping-pong ball water cannon

The course Phy Ex was created by Yves Couder in the Paris VII university to teach experimental physics through projects. In this article, we present this teaching method through a particular project that took place in the autumn semester 2019: the ping-pong ball water cannon. In this experiment, a glass containing water and a floating table tennis ball is dropped from some height to the ground. Following the impact, the ball is ejected vertically upwards at speeds that can be several times the impact speed. We report the student team's initial dimensional and order-of-magnitude analysis, and describe the successive experimental setups that showed (1) that free flight is essential for the phenomenon to occur, (2) that the order of magnitude of the ball ejection momentum is correctly predicted by a momentum balance based on integrating the pressure impulse during impact and (3) that making the ball surface more wettable, or stirring the liquid, drastically increases the momentum transfer. The proposed explanation, confirmed by direct high-speed video observations, is that the immersion depth of the ball increases during free fall due to capillary forces or vortex depression-in the absence of buoyancy-and that the enormous excess pressure on the bottom of the ball during impact drives the ball up towards its buoyancy equilibrium. The transfered momentum is sufficient to expel the ball at high velocity, very similar to the formation of liquid jets in collapsing cavities in liquids.

Mechanism of high velocity jet formation after a gas bubble collapse near the micro fiber immersed in a liquid

Numerical simulations of the vapor bubble collapse near the micro fiber immersed in a subcooled liquid allow us to propose the mechanism of formation of high velocity liquid jet previously observed in experiments. It is shown that spherical symmetry breaking of the velocity field near the fiber creates axisymmetric radially converged water flow resulting in appearance of the cumulative jet. Numerical simulations demonstrate that physical mechanism of jet formation is mainly determined by bubble surface dynamic and is irrespective to the processes driving bubble shrinking. Dependency of the jet velocity on time as well as effect of fiber thickness and initial vapor bubble radius on jet intensity are studied. It is found that optimal fiber thickness at which the jet is the most powerful exists. This optimal value is not universal but depends on initial vapor bubble radius.

Dynamic analysis of the primary breakup of an annular energetic liquid jet injecting into a confined space

The Large Eddy Simulation (LES) with the Volume of Fluid (VOF) method was carried out to investigate the primary breakup dynamic mechanism of an annular energetic liquid jet injecting into a confined space. The gas vortex structure and the liquid jet formation were visualized by tracking the evolution of the phase velocity and the interface location, and hence the coalescence process of the goblet-shaped liquid jet from the annular liquid jet was reproduced. Simulation results indicate that the first coalescence is caused by the Rayleigh-Taylor instability, which is generated by the interaction between the liquid jet head and the gas in the confined space. Two kinds of large-scale vortex structure expedite the secondary coalescence and the final goblet-shaped liquid jet form. Cavities are observed on the dense liquid jet column as a result of the coalescence on the upstream. Consequently, the droplet breakup occurs more frequently on the downstream liquid jet under the gas phase disturbance. The viscous shear is created by the aerodynamic interaction, and the regular fish-scale structure is presented under the Kelvin-Helmholtz instability, which promotes the bulge surface to break into droplets. The research reveals the dynamic mechanism of the annular energetic liquid jet structural destabilization observed in the previous experiments. The combination of the structural instability and the surface instability facilitate the primary breakup of the annular energetic liquid jet, which is beneficial to improve the atomization and the combustion performance.

Liquid jet formation during a suspended liquid suction process

In the tubular co-flowing gas-liquid jet, liquid is sucked through a nozzle suspended above the flat gas-liquid interface. The liquid hump can be induced by the sudden pressure change just beneath the nozzle entrance. At a sufficiently fast initial gas superficial velocity, the interface undergoes a transition and liquid starts to be sucked. The suction flow is in the form of an axisymmetric liquid jet surrounded by an upwards coaxial gas flow. In the present study, we discuss the evolution and characteristics of the suspended liquid suction flow. The jet dynamics include the interface deformation and development (the hump stage), the tubular co-flowing jet (the spout state) and the destabilization of the liquid jet (the jet state). Tube inner diameter, suspension height, and initial gas superficial velocity are three important parameters that influence the suction flow. Due to the inward gas flow, a relatively large amount of pressure gradients is imparted to a small mass of liquid near a free surface, which leads to interface deformation. The lateral boundary of the liquid hump circumferentially shrinks and the top liquid gradually rises following the shrinkage. There is a comparatively stable axisymmetric liquid jet surrounded by an upwards coaxial gas flow inside the tube. Surprisingly, no evidence is shown the dependence of jet spout with initial gas axisymmetric superficial velocity below the nozzle through plenty of experiment figures and statistical analysis. On the other hand, the velocity difference between the fast light gas flow and the slow dense liquid is critical to the destabilization of the liquid jet.

Dynamics of a spheroidal gas bubble near a rigid surface

Non-spherical dynamics of a bubble during its axisymmetric collapse near a planar rigid wall is considered. The liquid surrounding the bubble is ideal incompressible, its flow is potential. The pressure in the bubble is uniform, and varying with respect to adiabatic law. At the beginning of collapse, the bubble is spheroidal, the liquid is motionless. A numerical technique is applied, which is based on a stepwise method in time for calculating the bubble surface movement and on the boundary element method. The initial stage of the bubble collapse till the moment of contact between some parts of the bubble surface (i.e., till losing its one-connectedness) is considered. The effect of the ratio of the semi-axes of the spheroidal bubble and the initial thickness of the liquid layer between the bubble and the wall on the bubble shape, the pressure and velocity fields in liquid are investigated. The region of the problem parameters (the distance from the wall, the bubble non-sphericity) is outlined, in which the bubble collapses with formation of a cumulative liquid jet impacting on the bubble surface part nearest to the wall. The liquid pressures resulting from the impact are estimated.