Dynamics Of Bubble Collapse Research Articles

Impact of induced shock waves on cavitation bubble collapse dynamics and load characteristics

Impact of induced shock waves on cavitation bubble collapse dynamics and load characteristics

Dynamics of bubble collapse near an armored free surface

Armored surfaces refer to a liquid–air interface covered by a layer of floating particles. This paper examines the collapse dynamics of a bubble generated by an electric spark near such an armored surface. The collapse of the bubble near the armored surface is similar to that near a free surface, with the formation of spraying liquid film, upward liquid jet in the forms of water dome, water spike, and water skirt with the change of the vertical distance (l) from the bubble center to the liquid surface. However, on the armored surface, we also observe particle splash and solid–liquid mixture splash. We confirm that the particle splash occurs due to the transfer of shock wave energy during bubble expansion and collapse. The splashing velocity (vp) and the distance (d0) from the bubble center to the particle follow the scaling law of vp ∼ l/d02. Additionally, we discuss the motion of the upward liquid jet and downward vortex ring. We find that the armored surface only affects the initial velocity of the jet without affecting its acceleration. This can be attributed to the additional energy dissipation caused by the splash formed on the armored surface. In contrast, the trajectory of the vortex ring remains unaffected by the armored surface. This study provides valuable insights into the dynamics of bubble collapse near an armored surface and highlights the role of floating particles in altering the behavior of liquid jets.

Research on cavitation bubble behaviors between a dual-particle pair

The interactions between particle clusters and cavitation bubbles play an important role in several industrial applications, e.g., the abrasive erosion of hydraulic machinery, the efficiency improvement of ultrasonic cleaning, and the mineral flotation. This paper explores the influence of a dual-particle pair of unequal sizes on the bubble collapse dynamics based on a Kelvin impulse model and high-speed photography. The impact of the radius ratio of the dual-particle pair (ranging from 1.0 to 3.0), defined as the ratio of the large-particle radius to the small-particle radius, on the bubble interface deformation, collapse jet, and the translational movement of the bubble is analyzed. The main findings are as follows: (1) the Kelvin impulse based on the Weiss theorem can effectively predict the asymmetric bubble behaviors in terms of the moving distance and the direction of the bubble centroid during the bubble collapse; (2) the particle radius ratio is a key parameter affecting the intensity and direction of the Kelvin impulse, as well as the bubble centroid moving distance; and (3) the zero-Kelvin-impulse point is always biased toward the smaller particle in the dual-particle pair.

Modeling of shock wave produced by collapse of cavitation bubble using a fully conservative multiphase model

In this study, we extensively validated the applicability of the fully conservative compressible multiphase flow model to simulate the collapse of cavitation bubbles. The mathematical model is fully conservative, which is crucial for accurately modeling the strong shock phenomena induced via bubble collapse. The numerical method accounts for compressibility and mass transfer with phase-change transitions. A high-resolution shock-capturing finite-volume method and an accurate Riemann solver were employed to capture the strong shocks produced by bubble collapse. A grid-resolution study and validation were performed to ensure the convergence and consistency of the numerical method. This study focused on analyzing the shock waves generated during the collapse as well as the dynamics of bubble collapse and rebound. Quantitative comparisons between the simulation results and experimental data as well as the reference results revealed a high level of agreement. The investigation focused on the impact of various factors, including the bubble radius, phase change, and liquid pressure, on the collapse and rebound of the cavitation bubble, as well as the resulting shock waves. These analyses yielded valuable insight into the complex behavior of cavitation bubbles that collapse in a free field.

Numerical investigation of shock-induced bubble collapse dynamics and fluid–solid interactions during shock-wave lithotripsy

In this paper we investigate the bubble collapse dynamics under shock-induced loading near soft and rigid bio-materials, during shock wave lithotripsy. A novel numerical framework was developed, that employs a Diffuse Interface Method (DIM) accounting for the interaction across fluid–solid-gas interfaces. For the resolution of the extended variety of length scales, due to the dynamic and fine interfacial structures, an Adaptive Mesh Refinement (AMR) framework for unstructured grids was incorporated. This multi-material multi-scale approach aims to reduce the numerical diffusion and preserve sharp interfaces. The presented numerical framework is validated for cases of bubble dynamics, under high and low ambient pressure ratios, shock-induced collapses, and wave transmission problems across a fluid–solid interface, against theoretical and numerical results. Three different configurations of shock-induced collapse applications near a kidney stone and soft tissue have been simulated for different stand-off distances and bubble attachment configurations. The obtained results reveal the detailed collapse dynamics, jet formation, solid deformation, rebound, primary and secondary shock wave emissions, and secondary collapse that govern the near-solid collapse and penetration mechanisms. Significant correlations of the problem configuration to the overall collapse mechanisms were found, stemming from the contact angle/attachment of the bubble and from the properties of solid material. In general, bubbles with their center closer to the kidney stone surface produce more violent collapses. For the soft tissue, the bubble movement prior to the collapse is of great importance as new structures can emerge which can trap the liquid jet into induced crevices. Finally, the tissue penetration is examined for these cases and a novel tension-driven tissue injury mechanism is elucidated, emanating from the complex interaction of the bubble/tissue interaction during the secondary collapse phase of an entrapped bubble in an induced crevice with the liquid jet.

Influence of physical parameters on the collapse of a spherical bubble

This paper examines the influence of physical parameters on the collapse dynamics of a spherical bubble filled with diatomic gas (κ=7/5). The problem is formulated by the Rayleigh–Plesset dynamical equation, whose numerical solutions are carried out by Maple. Our studies show that each physical parameter affects the bubble collapse dynamics in different degree, which reveals that bubble collapse dynamics must considers all the parameters including liquid viscosity, surface tension, etc, else the outcome cannot be trusted.

Experimental study of the influence of mesoscale surface structuring on single bubble dynamics

In this study, we proposed a passive control method to control the dynamics of a laser-induced single cavitation bubble using mesoscale surface structuring. For this aim, we experimentally investigated the effects of different mesostructured V-shaped riblets on the dynamics of a laser-induced single cavitation bubble at four different relative wall distances. First, we captured the dynamics of a single cavitation bubble near a flat solid surface using a high-speed camera. Second, we analyzed the dynamics of a single cavitation bubble near the mesostructured riblets at different relative wall distances and compared with the bubble collapse dynamics near the flat solid surface. The results showed that the bubble dynamics near the riblets were different from the bubble dynamics near the flat solid surface. In addition, the microjet towards the riblet surface and the inclined or vertical jet after the first collapse were manipulated through the effects of riblets. This means the riblet structures can suppress or mitigate the microjet impact which can be formed during the first collapse near the riblet surface.

Cavitation bubble interaction with compliant structures on a microscale: A contribution to the understanding of bacterial cell lysis by cavitation treatment

Numerous studies have already shown that the process of cavitation can be successfully used for water treatment and eradication of bacteria. However, most of the relevant studies are being conducted on a macro scale, so the understanding of the processes at a fundamental level remains poor. In attempt to further elucidate the process of cavitation-assisted water treatment on a scale of a single bubble, the present paper numerically addresses interaction between a collapsing microbubble and a nearby compliant structure, that mechanically and structurally resembles a bacterial cell. A fluid–structure interaction methodology is employed, where compressible multiphase flow is considered and the bacterial cell wall is modeled as a multi-layered shell structure. Simulations are performed for two selected model structures, each resembling the main structural features of Gram-negative and Gram-positive bacterial cell envelopes. The contribution of two independent dimensionless geometric parameters is investigated, namely the bubble-cell distance δ and their size ratio ς. Three characteristic modes of bubble collapse dynamics and four modes of spatiotemporal occurrence of peak local stresses in the bacterial cell membrane are identified throughout the parameter space considered. The former range from the development of a weak and thin jet away from the cell to spherical bubble collapses. The results show that local stresses arising from bubble-induced loads can exceed poration thresholds of cell membranes and that bacterial cell damage could be explained solely by mechanical effects in absence of thermal and chemical ones. Based on this, the damage potential of a single microbubble for bacteria eradication is estimated, showing a higher resistance of the Gram-positive model organism to the nearby bubble collapse. Microstreaming is identified as the primary mechanical mechanism of bacterial cell damage, which in certain cases may be enhanced by the occurrence of shock waves during bubble collapse. The results are also discussed in the scope of bacteria eradication by cavitation treatment on a macro scale, where processes of hydrodynamic and ultrasonic cavitation are being employed.

Cavitation Plays a Vital Role in Stone Dusting During Short Pulse Holmium:YAG Laser Lithotripsy.

Objective: To investigate the mechanism of stone dusting in Holmium (Ho): YAG laser lithotripsy (LL). Materials and Methods: Cylindrical BegoStone samples (6 × 6 mm, H × D) were treated in water using a clinical Ho:YAG laser lithotripter in dusting mode (0.2-0.4 J with 70-78 μs in pulse duration, 20 Hz) at various fiber tip to stone standoff distances (SD = 0, 0.5, and 1 mm). Stone damage craters were quantified by optical coherence tomography and bubble dynamics were captured by high-speed video imaging. To differentiate the contribution of cavitation vs thermal ablation to stone damage, three additional experiments were performed. First, presoaked wet stones were treated in air to assess stone damage without cavitation. Second, the laser fiber was advanced at various offset distances (OSD = 0.25, 1, 2, 3, and 10 mm) from the tip of a flexible ureteroscope to alter the dynamics of bubble collapse. Third, stones were treated with parallel fiber to minimize photothermal damage while isolating the contribution of cavitation to stone damage. Results: Treatment in water resulted in 2.5- to 90-fold increase in stone damage compared with those produced in air where thermal ablation dominates. With the fiber tip placed at OSD = 0.25 mm, the collapse of the bubble was distracted away from the stone surface by the ureteroscope tip, leading to significantly reduced stone damage compared with treatment without the scope or with scope at large OSD of 3-10 mm. The average crater volume produced by parallel fiber orientation at 0.2 J after 100 pulses, where cavitation is the dominant mechanism of stone damage, was comparable with those produced by using perpendicular fiber orientation within SD = 0.25-1 mm. Conclusion: Cavitation plays a dominant role over photothermal ablation in stone dusting during short pulse Ho:YAG LL when 10 or more pulses are delivered to the same location.

Mechanism of material deformation during cavitation bubble collapse

This research is devoted to understanding the physical mechanism of cavitation erosion in liquid flows at the fundamental scale of cavitation bubble collapse. Cavitation bubbles form in a liquid when the pressure of the liquid decreases locally below the saturated vapor pressure pvsat. The bubbles grow due to low ambient pressure and collapse when the surrounding liquid pressure increases again above pvsat. Bubble collapse near solid walls can result in high velocity liquid jet and shock wave emission that cause high pressure loads on the wall. These pressure loads are responsible for the erosive damages on solid surfaces, as observed in applications like liquid fuel injection, hydrodynamic power generation and marine propulsion. On the other hand, the pressure loads from collapsing bubbles are exploited for applications like shock wave lithotripsy, drug delivery and cleaning surfaces. In this work, we follow a numerical approach, which begins with the development of a compressible solver capable of resolving the cavitation bubbles in the finite-volume code YALES211http://yales2.coria-cfd.fr. employing a simplified homogeneous mixture model. The solid material response to cavitation loads is resolved with the finite element code Cast3M22http://www-cast3m.cea.fr.. A one–way coupling approach for fluid–structure interaction (FSI) simulation between the fluid and solid domains is pursued. In this simple approach, the pressure field computed by the fluid solver at the fluid–solid interface is communicated to the solid solver which computes the deformation induced in the material. In the end, the dynamical events responsible for surface deformation are highlighted from 2D vapor bubble collapse dynamics and associated pressure loads on the solid wall are estimated. The response of different materials to bubbles collapsing at different distances from the solid wall is discussed.

Effect of stand-off distance on “counterjet” and high impact pressure by a numerical study of laser-induced cavitation bubble near a wall

In experiments of the collapse and rebound of a laser-produced cavitation bubble near a wall, a so-called “counterjet”, i.e., a jet in the direction away from the bubble and the wall, was typically observed during the rebound phase for a certain range of stand-off distances. It was previously suggested that a mechanism for the formation of the counterjet might be cavitation inception that follows the self-penetration of the jet torus shock wave. Numerical simulations in the current work show that this counterjet may in fact be part of the bubble spiral trailing behind the main part as the bubble is distorted by the ring vortex and becomes toroidal in shape after the initial collapse. Since the spiral is trailing behind the main bubble, it appears to be a jet in the direction away from the bubble and the wall, giving the impression of the formation of a counterjet. However, the simulations show that the velocities in the spiral are also towards the wall. The effects of phase transition on various aspects of bubble collapse dynamics are also examined. It is found that the experimental bubble-wall distance evolution can only be better captured through the inclusion of phase transition modeling. Without phase transition, the bubble-wall distance history in the simulations diverges from the experimental one upon the first collapse. After these validations, the effects of stand-off distance on the impact pressure are studied systematically with results compared with experiments. It is found that the largest impact pressures can be as high as 1–2 GPa as a result of the strong focus of a nearly spherical shock onto the symmetry axis and along the wall that occurs when the stand-off distances are low with Ho/Ro<0.1. The impact pressure of ∼0.1 GPa at Ho/Ro<0.7 on the other hand is found to be the result of the focus of the ring-vortex-focusing shock onto the symmetry axis. Both the magnitude of the impact pressure and the respective stand-off distance range are consistent with previous experimental results.

Dynamic Characteristics of Bubble Collapse Near the Liquid-Liquid Interface

Bubble collapse near the liquid-liquid interface was experimentally studied in this paper, and the dynamic evolution of a laser-induced bubble (generation, expansion, and collapse) and the liquid-liquid interface (dent and rebound) were captured by a high-speed shadowgraph system. The effect of the dimensionless distance between the bubble and the interface on the direction of the liquid jet, the direction of bubble migration, and the dynamics of bubble collapse were discussed. The results show that: (1) The jet generated during bubble collapse always directs toward the denser fluid; (2) bubble collapses penetrate the interface when the bubble is close to the interface; (3) three different shapes of the liquid-liquid interface—that is, a mushroom-shaped liquid column, a spike droplet, and a spherical liquid droplet—were observed.

Cavitation bubble interaction with a rigid spherical particle on a microscale

Cavitation bubble collapse close to a submerged sphere on a microscale is investigated numerically using a finite volume method in order to determine the likelihood of previously suspected mechanical effects to cause bacterial cell damage, such as impact of a high speed water jet, propagation of bubble emitted shock waves, shear loads, and thermal loads. A grid convergence study and validation of the employed axisymmetric numerical model against the Gilmore’s equation is performed for a case of a single microbubble collapse due to a sudden ambient pressure increase. Numerical simulations of bubble-sphere interaction corresponding to different values of nondimensional bubble-sphere standoff distance δ and their size ratio ε are carried out. The obtained results show vastly different bubble collapse dynamics across the considered parameter space, from the development of a fast thin annular jet towards the sphere to an almost spherical bubble collapse. Although some similarities in bubble shape progression to previous studies on larger bubbles exist, it can be noticed that bubble jetting is much less likely to occur on the considered scale due to the cushioning effects of surface tension on the intensity of the collapse. Overall, the results show that the mechanical loads on a spherical particle tend to increase with a sphere-bubble size ratio ε, and decrease with their distance δ. Additionally, the results are discussed with respect to bacteria eradication by hydrodynamic cavitation. Potentially harmful mechanical effects of bubble-sphere interaction on a micro scale are identified, namely the collapse-induced shear loads with peaks of a few megapascals and propagation of bubble emitted shock waves, which could cause spatially highly variable compressive loads with peaks of a few hundred megapascals and gradients of 100 MPa/μm.

Numerical Simulation of Vapor–Bubble Collapse—Heat Transfer and Nonlinear Dynamics Issues

Abstract In this work, we compute the dynamics of a spherical vapor-bubble in an infinite pool of subcooled water during bubble collapse using our semi-analytical method. The main contribution of this work is to bring out the dynamics of nonmonotonic bubble collapse describing heat transfer characteristics and nonlinear dynamics. The dynamics shows the variation of radius with time for collapsing vapor bubble at different subcooling ΔTsub of 1.40 K to 35 K. The present approach accurately determines the bubble radius decreasing with time and has been compared with our experimental results, the experiment from literature, the other theories, and correlations. As it is noted that the literature lacks steady-state analysis of oscillating bubble collapse, we also report the steady-state analysis and the bifurcation analysis of bubble collapse at a pressure of 1.0 atm to check the stability of bubble collapse. The effect of ΔTsub and initial bubble radius R0 on dynamics of bubble collapse has been analyzed. The collapse of big bubbles involves with the bubble oscillations because of a large contribution of liquid inertia and the collapse of very small bubbles essentially occurs in heat transfer regime.

In-situ observation of collective bubble collapse dynamics in a quasi-two-dimensional foam

The stability of foams is an important subject not only for fundamental science, but for applications in daily life. The most destructive phenomenon underpinning foam collapse is a collective bubble collapse, yet the mechanism behind this is unclear. In this study, we clarify the dynamics of the collective bubble collapse in a quasi-two-dimensional foam by in-situ observation with a high speed camera. We find two modes for collective bubble collapse: one is the propagation of liquid film breakage via impact with the stream of another broken liquid film. The other is breakage of a distant liquid film due to penetration by a liquid droplet, emitted by impact with the flow of a broken liquid film. As the liquid fraction increases, the velocity of liquid droplets decreases. Instead of penetration, the liquid droplet bounces like a billiard ball or it is absorbed into other films.

Interaction of a spark-generated bubble with a two-layered composite beam

This paper deals with interaction between a spark-generated bubble and a two-layered composite beam (constrained at its two ends) which consists of an aluminum sheet coated by an elastic layer. Both numerical and experimental approaches are employed to investigate the dynamics of bubble collapse near the two-layered composite beam. A good agreement between the numerical simulation and experimental observation is achieved, which reveals that the bubble collapse time is greatly influenced by the nearby two-layered composite beam. The numerical model is then extended to examine the dynamic response of the two-layered composite beam induced by the bubble growth and collapse; and also to explore the correlation between the energy density of the two-layered composite beam and its coating layer stiffness. The results from this study may provide some insights on the protection of submerged marine structures exposed to bubble collapse arising from an underwater explosion.

Influence of the size dependence of surface tension on the dynamics of a bubble in a liquid

The Gibbs dividing surface method is used to derive the differential equation defining the dependence of the surface tension of a bubble in a nonpolar single-component liquid on its radius. Exact and asymptotic solutions of this equation have been obtained. It follows from the calculations that the bubble surface tension increases with decreasing radius. The Rayleigh-Plesset equation describing the bubble collapse dynamics is solved numerically by taking into account the size dependence of surface tension. The size dependence of surface tension is shown to affect significantly the final bubble collapse stage and, on the whole, accelerates this process.

Free-Lagrange simulations of the expansion and jetting collapse of air bubbles in water

A free-Lagrange numerical method is implemented to simulate the axisymmetric jetting collapse of air bubbles in water. This is performed for both lithotripter shock-induced collapses of initially stable bubbles, and for free-running cases where the bubble initially contains an overpressure. The code is validated using two test problems (shock-induced bubble collapse using a step shock, and shock–water column interaction) and the results are compared to numerical and experimental results. For the free-running cases, simulations are conducted for a bubble of initial radius 0.3 mm located near a rigid boundary and near an aluminium layer (planar and notched surfaces). The simulations suggest that the boundary and its distance from the bubble influence the flow dynamics, inducing bubble elongation and jetting. They also indicate stress concentration in the aluminium and the likelihood of aluminium deformation associated with bubble collapse events. For the shock-induced collapse, a lithotripter shock, consisting of 56 MPa compressive and −10 MPa tensile waves, interacts with a bubble of initial radius 0.04 mm located in a free field (case 1) and near a rigid boundary (case 2). The interaction of the shock with the bubble causes it to involute and a liquid jet is formed that achieves a velocity exceeding 1.2 km s−1 for case 1 and 2.6 km s−1 for case 2. The impact of the jet on the downstream wall of the bubble generates a blast wave with peak overpressure exceeding 1 GPa and 1.75 GPa for cases 1 and 2, respectively. The results show that the simulation technique retains sharply resolved gas/liquid interfaces regardless of the degree of geometric deformation, and reveal details of the dynamics of bubble collapse. The effects of compressibility are included for both liquid and gas phases, whereas stress distributions can be predicted within elastic–plastic solid surfaces (both planar and notched) in proximity to cavitation events. There is a movie with the online version of the paper.

Ultrasound induced cavitation and sonochemical yields

The introduction of a strong acoustic field to an aqueous solution results in the generation of cavitation microbubbles. The growth and collapse of these microbubbles focuses and transfers energy from the macroscale (acoustic wave) to the microscale (vapor inside the bubbles) producing extremely high localized pressures and temperatures. This unique energy focusing process generates highly reactive free radicals that have been observed to significantly enhance chemical processing. This paper presents a model that combines the dynamics of bubble collapse with the chemical kinetics of a single cavitation event. The effects on sonochemical yields and bubble dynamics of gas composition and heat transfer are assessed and compared with previous theoretical and experimental studies. Results from this model are used to explain unusual experimentally observed sonochemical phenomena.

Bubble hydrodynamics and the confined electron model for sonoluminescence

The origin of sonoluminescence, the conversion of acoustic energy into ultraviolet/visible radiation in liquids, has remained elusive. It is proposed that the emission arises from electrons confined to voids in the hot, dense fluid formed during the final stages of bubble collapse. Such electrons are produced by high-temperature ionization of the bubble constituents. A hard sphere-based model was developed for the fluid structure, thermodynamics, and confined electron emission. The model is consistent with the observed spectral distributions, power output, and time scale associated with emission from single cavitating rare gas bubbles. Effective temperatures during emission in the 200- to 700-nm spectral window are predicted to range from 20 000 to 60 000 K. The consistency of the confined electron model for single bubble sonoluminescence with the observed dynamics of bubble collapse is also explored. The key aspect of this approach is the treatment of the collapsed bubble as a true fluid. The hydrodynamics of bubble collapse are modeled with a modified Rayleigh–Plesset equation using improved formulations for the equation of state and specific heat ratio. Results are presented for the rare gases and related to experimental observations.