Collapse Of Cavitation Bubbles Research Articles

Experimental study on cavitation characteristics and pressure load of actively ventilated double-vehicle configuration during water exit

The cavitation phenomenon is widely observed in the cross-medium movement of vehicles, seriously affecting their structural safety and motion stability. Attempts to control these effects include active ventilation, although existing research on active ventilation techniques has focused on single-vehicle configurations. In real situations, multiple vehicles may exit the water at the same time. However, the cavitation development process of the double vehicles during the water exit is completely different from that of the single vehicle, and the flow field around it is also quite different. Therefore, it is necessary to research the water-exit process of actively ventilated double-vehicle configurations. In this article, a double-vehicle water-exit device that injects high-pressure gas is designed, and the factors influencing changes in the cavitation bubbles are studied, such as the launch speed and environmental pressure. The water exit of a single vehicle under the same conditions is considered as the control case. According to our results, active ventilation effectively relieves the cavitation suppression phenomenon between the two vehicles, and reduces the pressure peak at which the cavitation bubbles collapse. Factors such as the launch speed, environmental pressure, and ventilation rate have a significant influence on the development of cavitation bubbles, especially their size. The influence of these factors on the pressure is mainly realized by changing the thickness of the cavity and the initial pressure.

Hydroelasticity effects induced by a single cavitation bubble collapse

To investigate hydroelasticity effects on a single cavitation bubble dynamic, a focused laser was used to generate the bubble in water near a flexible aluminium foil fixed to a specimen holder with a circular aperture to allow the foil to vibrate. The bubble was generated below the foil's center. A laser-based optical sensor measured the displacement at the center of the foil. Simultaneously, a high-speed camera monitored the bubble's dynamics to correlate it with the foil's displacement. By directly measuring the foil's displacements, we provided building block missing in previous investigations. We found that a key difference between bubble dynamics near a rigid and an elastic structure was that, at relative wall distances larger or equal to unity, the bubble did not collapse on the elastic foil. The bubble's dynamics caused dominant foil displacements during its first growth (after plasma seeding) and during its subsequent collapse. Foil displacements during the bubble's first collapse were about twice as large as those during its growth phase. For lower relative wall distances, the induced foil displacements were significant until the bubble's third collapse. At larger relative wall distances, the bubble did not collapse on the elastic foil and, thus, it did not induce erosion. However, it caused foil vibrations and, therefore, may contribute to the foil's structural fatigue damage. Our study postulates that the cavitation may not be erosive, however it can induce impulsive loads causing vibrations and thereby fatigue damage of nearby structures.

Wall vortex induced by the collapse of a near-wall cavitation bubble: Influence of the water surface

Wall vortex induced by the collapse of a near-wall cavitation bubble: Influence of the water surface

Simulation of bubble oscillations in cavitation-induced acoustic fields

Understanding bubble oscillations is critical in science, engineering and medicine. An important aspect of bubble dynamics is the transition from spherical to non-spherical oscillations when the bubble is subjected to external stimuli like time-dependent pressure fields. The mechanisms underpinning this process are not well understood for the complex pressure fields encountered in most applications. Here, we perform high-fidelity numerical simulations of the oscillations of a non-condensable gas bubble induced by the acoustic field generated by the collapse of a nearby cavitation bubble. We compare our simulation results with controlled laboratory experiments and demonstrate that our computational approach predicts spatial and temporal bubble oscillation patterns. This work opens new opportunities to understand the oscillation of bubbles induced by complex acoustic fields.

A study on the hydroacoustic characterisation of a cavitating propeller by dynamic adaptive mesh refinement technique

Underwater radiated noise (URN) of a marine propeller has received significant interest in recent decades due to its implications on marine fauna. Therefore, an accurate prediction of URN at an early stage of the propeller design is becoming imperative. This study presents a numerical investigation into the noise prediction of a marine propeller, including cavitation and a comparison with experimental test results obtained from the URN database from the King's College D (KCD) standard propeller series. Amongst the propellers tested in the series, the member KCD-193 was chosen to scrutinise in this study due to the significant variance of the cavitation types experienced by this propeller member and consequent characteristic variations observed in its URN spectral response. Numerical URN predictions of different flow conditions, represented by the advance coefficient and cavitation number, were conducted to investigate their effects on the noise spectrum. These predictions were compared with the experimental results to enable interpretation of the impact of various aspects of the simulation on URN prediction accuracy. In this investigation, one of the most prominent noise sources, tip-vortex cavitation (TVC), was identified as a critical aspect that needs to be captured by the numerical simulations for accurate URN predictions using CFD simulations. The influence of TVC on the spectrum was observed to be significant. The inception and stable presence of TVC dominated the frequency response of the broadband hump. In order to address this, a systematic adaptive mesh refinement strategy was implemented based on the vortex criterion to solve the flow characteristics in the propeller slipstream accurately. To further complement this task, a correlation between the cavitation bubble growth and collapse phenomenon by the sensitivity of the broadband hump on the spectrum was established based on the experimental results. The central frequency of the broadband hump was observed to vary with the advance coefficient and cavitation number. The reduction in the cavitation number resulted in a shift of this hump towards lower frequencies. The URN level of the hump decreased slightly in the high frequency by the reduction in the advance coefficient and the developing cavitation, demonstrating the cushioning effect on the spectrum. An accurate assessment of the noise spectrum, as far as numerical predictions are concerned, particularly on the broadband hump frequency bandwidth, was directly associated with the resolution of the TVC.

Velocity characteristics of microjets generated by double bubbles near a rigid wall under ultrasound

The cavitation bubble collapse and associated microjets are widely used in ultrasound and chemical engineering. However, much remains to be known about the interplay of double bubbles and their microjets. The dynamic models for the single-bubble and double-bubble near the rigid wall under ultrasound were constructed and numerically solved to reveal the bubble collapse behavior. Results indicates that compared to a free wall, rigid walls have a strong inhibitory effect on the collapse of a single bubble, but have a certain promoting effect on the collapse of double bubbles. The double bubbles have a higher velocity and smaller range of initial bubble radii than a single bubble to produce microjets. When the bubble is close to the stiff wall, the microjet of a single bubble is always stronger than that of double bubbles. But when bubbles move away from rigid walls, the microjet velocity of double bubbles may be greater than that of a single bubble. Compared with the single bubble, the double bubbles can generate microjets with a narrower range of the ultrasound pressure amplitude and a smaller ultrasound frequency. The study will give new insights into the velocity of microjets in ultrasonic related processing applications.

Ultrasonic dehydration of materials without liquid-vapor transition

This study validates the mechanism of ultrasonic dehydration without transition of water into vapor. The process can be realized by cavitation dispersion of liquid initiated by collapse of cavitation bubbles of cylindrical shape formed in capillaries. The developed mathematical model considers the complete life cycle of cavitation bubbles, encompassing three stages: slow growth, rapid expansion with deformation, and collapse. The optimum range of sound pressure level from 150 dB (critical level) to 170 (limit level) at which cavitation dispersion of liquid from capillaries takes place has been determined. The optimum sample size corresponding to the ultrasonic wavelength in gas, at which the dehydrated productivity is maximized, has been determined. The mechanism of ultrasonic dispersion of liquid during drying was confirmed by experiments. Practical implementation of ultrasonic drying of food products (carrots) confirmed effectiveness of implementation of dehydration mechanism and provided a reduction of drying time by 1.9 times with a reduction of power consumption by 1.7 times.

Morphological analysis for thermodynamics of cavitation collapse near fractal solid wall

A fractal geometric boundary with natural wall features is introduced into a hybrid lattice-Boltzmann-method (LBM) multiphase model. The physical model of cavitation bubble collapse near the irregular geometric wall is established to study the thermodynamic characteristics of the bubble collapse. Due to the lack of periodicity, symmetry, spatial uniformity and obvious correlation in the LBM simulation of the bubble collapse near the fractal wall, the morphological analysis based on Minkowski functional is introduced into the thermodynamic investigation of cavitation bubble so as to analyze and obtain the effective information. The results show that the Minkowski functional method can employed to study the temperature information in complex physical fields hierarchically and quantitatively. The high/low temperature region of the cavitation flow is explored, and thermal effect between irregular and fractal geometric wall and cavitation bubble can be revealed. It illustrates that LBM and morphological analysis complement each other, and morphological analysis can also be used as an optional and potential tool in research field of complex multiphase flows.

The collapse of a sonoluminescent cavitation bubble imaged with X-ray free-electron laser pulses

Single bubble sonoluminescence (SBSL) is the phenomenon of synchronous light emission due to the violent collapse of a single spherical bubble in a liquid, driven by an ultrasonic field. During the bubble collapse, matter inside the bubble reaches extreme conditions of several gigapascals and temperatures on the order of 10000 K, leading to picosecond flashes of visible light. To this day, details regarding the energy focusing mechanism rely on simulations due to the fast dynamics of the bubble collapse and spatial scales below the optical resolution limit. In this work we present phase-contrast holographic imaging with single x-ray free-electron laser (XFEL) pulses of a SBSL cavitation bubble in water. X-rays probe the electron density structure and by that provide a uniquely new view on the bubble interior and its collapse dynamics. The involved fast time-scales are accessed by sub-100 fs XFEL pulses and a custom synchronization scheme for the bubble oscillator. We find that during the whole oscillation cycle the bubble’s density profile can be well described by a simple step-like structure, with the radius R following the dynamics of the Gilmore model. The quantitatively measured internal density and width of the boundary layer exhibit a large variance. Smallest reconstructed bubble sizes reach down to R≃0.8μm , and are consistent with spherical symmetry. While we here achieved a spatial resolution of a few 100 nm, the visibility of the bubble and its internal structure is limited by the total x-ray phase shift which can be scaled with experimental parameters.

Investigations on the jets and shock waves of a cavitation bubble collapsing between a wall and a particle

The simultaneous presence of particles and cavitation bubbles has a deleterious effect on the performance and safety of hydraulic machinery through the generation of jets and shock waves. In the present paper, the mechanisms responsible for the generation and the evolution of jets and shock waves from a collapsing cavitation bubble situated between a spherical particle and a wall are simulated using a compressible two-phase flow solver. Specifically, the effects of bubble position on jet and shock wave behavior are qualitatively analyzed. The simulations and experiments reveal three typical cases of jet behavior: a jet toward the wall, double jets, and a jet toward the particle. Needle jets and shock waves are commonly generated by collisions of the bubble interface. In some cases, needle jets are associated with a high impact velocity. It is found that the smaller the distance between the particle and the wall, the higher the pressure generated by the jets and the shock waves on the wall.

Cavitation bubble collapse near a rigid wall with an oil layer

This paper reports on the study of a laser-generated cavitation bubble in water collapsing near a rigid wall that is covered with a layer of silicone oil. The oil viscosity is between 5 and 5000 cSt. It is known that a collapsing cavitation bubble near a rigid boundary develops a jet. In this study, we show that the viscous oil layer competes with the flow generated by the bubble, and affects the short- and long-term bubble dynamics. For very low viscosity silicone oil (5, 10 and 20 cSt) the vortices formed when the water jet hits the wall result in a gas–water mixture in the oil layer. With increasing viscosity, i.e. 50 and 100 cSt, the formation of water droplets with gas bubbles inside the oil layer is observed. The bubble dynamics and flow in the oil layer are nicely reproduced with VoF simulations up to the second bubble collapse. In higher viscosity silicone oils (350, 500 and 1000 cSt), the water jet typically retracts completely during the re-expansion of the bubble. When a very high viscosity oil (5000 cSt) is used, a ‘mushroom’-shaped bubble is formed in water which splits in two as it collapses. To separate the regimes, we introduce a non-dimensional stress ratio relating the inertia and viscosity. This inverse Reynolds number Π becomes approximately 1 in the jet retraction regime. When Π≥ 1.0, the jet impact and vortices are effectively hindered on the rigid wall.

Three-dimensional modelling of cavitation bubble collapse using non-orthogonal multiple-relaxation-time lattice Boltzmann method

In this study, we employ a three-dimensional (3D) non-orthogonal multiple relaxation time (MRT) pseudo-potential lattice Boltzmann (LB) model to simulate the dynamics of cavitation bubble evolution. We benchmark the model against the Laplace law and the Rayleigh–Plesset (R–P) equation, confirming its efficacy in accurately capturing cavitation phenomena. We then apply the model to examine the collapse dynamics of a singular bubble located near a plane wall boundary and right-angled wall corner. Additionally, the dynamic interactions among five cross-shaped bubbles revealed the dimensionless jet volume Vj*, which is the ratio of the jet volume to the maximum bubble volume, exhibits a power relationship with the bubble distance δ. The simulation results demonstrate the accuracy of the model in discerning the effect of the wall boundary and the protective mechanisms inherent to multi-bubble interactions. These results further validate the aptness of the model for cavitation bubble dynamics simulations. Moreover, the tested case studies provide a foundational basis for future research into more complex cavitation behaviours. In summary, the developed 3D non-orthogonal MRT pseudo-potential LB model is capable of reproducing fluid flows, capturing pressure waves, and measuring wall pressures. Our work provides a deep insight into cavitation bubble dynamics and a solid basis for both applied and fundamental research.

Fluid–solid coupling analysis of submerged water jet cavitation micro-forming

Submerged cavitating waterjet micro-forming is a novel jetting technology. Existing detection devices cannot accurately detect bubble distribution in still water domains and target workpiece processing areas. To investigate bubble generation and distribution in still water domains and their influence on target micro-forming, a submerged cavitating waterjet micro-forming fluid–solid coupling numerical model was established in this paper. The distribution of submerged cavitating waterjet cavitation effects and the hammering of micro waterjets on metal plates under the action of cavitation bubbles, as well as the coupled forces, were analyzed. The results show that bubble distribution in still water domains is closely related to turbulence, vortices, and pressure distributions. The collapse of cavitation bubbles generates enormous pressure, and the pressure generated by the collapse of cavitation bubbles causes the micro waterjet hammers to produce annular deformation zones on the metal plates. The bubble distribution laws and theoretical basis of cavitation micro-forming technology in submerged waterjets are provided in this study, which has very important engineering application significance.

Experimental and computer study of the mechanism and identification of conditions for energy-efficient removal of moisture from materials under ultrasonic exposure.

The article is devoted to investigation of energy-efficient moisture removal from capillary-porous materials. Moisture is removed by dispersion at collapse of cylindrical cavitation bubbles, formed by ultrasonic vibrations in the capillaries of the material. Mathematical model, which allowed to investigate the mechanism of moisture dispersion, has been developed. Necessity of realization of cavitation bubble full life cycle in capillary (slow growth, rapid expansion with deformation, collapse) was found. An optimal range of sound pressure levels from 150 dB ("critical level" at which dispersion of water from capillary starts) up to 170 dB (dispersion productivity growth stops due to cavitation bubbles reaching maximum size equal to diameter of capillary) was determined. It is shown that the size of the dewatered sample for maximum drying efficiency should correspond to the ultrasonic wavelength in air. Ultrasonic dispersion of liquid during drying was confirmed experimentally. It is found that for significant reduction of drying time (up to 50% and more) it is necessary to affect in the range of 165-170 dB. And the materials to be dried must be placed as particles or layers having dimensions or thicknesses corresponding to the length of the ultrasonic wave in air. The implementation of ultrasonic drying, on the example of food products (beets) provided a reduction in drying time of 1.9 times, while reducing energy costs by 1.7 times in comparison with convective drying.

Shake, shear, and grind! - the evolution of mechanoredox polymerization methodology.

In the last half decade, mechanoredox catalysis has enabled an entirely new genre of polymerization methodology. In this paradigm, mechanical force, such as ultrasonic cavitation bubble collapse or ball mill grinding, polarizes piezoelectric nanoparticles; the resultant piezopotential drives the redox processes necessary for free- and controlled-radical polymerizations. Since being introduced, evolution of these methods facilitates exploration of mechanistic underpinnings behind key electron-transfer events. Mechanical force has not only been identified as a "greener" alternative to more traditional reaction stimuli (e.g., heat, light) for the synthesis of commodity polymers, but also a potential technology to enable the production of novel thermoplastic and thermoset materials that are either challenging, or even impossible, to access using conventional solution-state approaches. In this Feature Article, significant contributions to such methods are highlighted within. Advances and ongoing challenges in both ultrasound and ball milling driven reactions for radical polymerization and crosslinking are identified and discussed.

Numerical Simulation of Cavitation Bubble Collapse inside an Inclined V-Shape Corner by Thermal Lattice Boltzmann Method

Cavitation happening inside an inclined V-shaped corner is a common and important phenomenon in practical engineering. In the present study, the lattice Boltzmann models coupling velocity and temperature fields are adopted to investigate this complex collapse process. Based on a series of simulations, the fields of density, pressure, velocity and temperature are obtained simultaneously. Overall, the simulation results agree with the experiments, and they prove that the coupled lattice Boltzmann models are effective to study cavitation bubble collapse. It was found that the maximum temperature of bubble collapse increases approximately linearly with the rise of the distance between the single bubble center and the corner. Meanwhile, the velocity of the micro-jet increases and the pressure peak at the corner decreases correspondingly. Moreover, the effect of angle of the V-shaped wall on the collapse process of bubbles is similar to the effect of distance between the single bubble center and the corner. Moreover, with the increase in bubble radius, the maximum temperature of bubble collapse increases proportionally, the starting and ending of the micro-jet are delayed and the pressure peak at the corner becomes larger and also is delayed. In the double bubble collapse, the effect of distance between two bubble centers on the collapse process of bubbles is discussed in detail. Based on the present study, appropriate measures can be proposed to prevent or utilize cavitation in practical engineering.

Dynamic behaviors of cavitation bubbles near biomimetic surfaces: A numerical study

This work is devoted to numerical studies of dynamic behaviors of underwater cavitation bubbles and the associated fluid flow phenomena such as high-speed liquid jet and pressure loads characteristics near biomimetic shark skin surfaces. Potential damages to the surface caused by cavitation bubbles are numerically quantified by the pressure peak, pressure duration and pressure impulse at the surface center. This work utilizes a compressible VOF multiphase model in conjunction with user defined functions (UDFs). The model has been validated against published experimental data in terms of bubble morphological evolution and the time-dependent liquid film thickness. The results reveal that the shark skin-inspired surfaces have important influence on bubble dynamics, water jets and shock wave pressures under various stand-off parameters. Violent deformation and splashing of the bubbles with weak liquid jet impact and pressure impulse can be observed on the surface covered with triangular shaped structures, accompanied by a certain degree of attenuation on the impacting strength and range of the shock waves. Additionally, the migrating and coalescing behaviors of bubble pairs are reduced with the increase of the initial interbubble distance. The large bubble–wall distance can considerably alter the direction of the microjet flow away from the shark skin-inspired surface. These findings shed the light for designing and controlling of multiple cavitation bubbles collapse near biomimetic surfaces of high-speed marine applications.

Acceleration mechanism of abrasive particle in ultrasonic polishing under synergistic physical vibration and cavitation: Numerical study

Ultrasonic technology is widely applied in the engineering ceramic polishing processes without the limitation of material properties and ideally integrated into computer numerical control system. Ultrasonic-induced cavitation and mechanical vibration effect could accelerate the motion of solid abrasives. The individual behaviors of microjet/shockwave of ultrasonic cavitation in gases and liquids, and micro-abrasives with simple harmonic vibrations in solids and liquids has been extensively studied. To conduct a systematic and integrated study of abrasives behavior in the polishing contact region involving abrasive, surround-workpiece wall, ultrasonic physical vibration, and ultrasonic cavitation impact, a novel model integrating the free abrasive motion velocity and fixed abrasive indentation depth under multi-scale contact was proposed according to Hertzian contact theory, Greenwood-Williamson model, indentation deformation theory, the basic equations of cavitation bubble dynamics, cavitation impact control equations, and Newton's law of motion equation. The effects of ultrasonic amplitude, ultrasonic frequency, preloading force and particle size on the proposed model were investigated by theoretical analysis and numerical simulations. Ultrasonic physical vibration mainly influences the dynamic gap and further influence the number of different abrasives. Furthermore, the indentation depth of fixed abrasive depends mainly on the abrasive geometry. As the contact gap and abrasive size decrease, the indentation depth gradually decreases. Under the synergistic effect of cavitation-induced shock wave and microjet, the velocity of free abrasive in this paper is generally 0–150 m/s, and the kinetic energy of free abrasive increases roughly linearly with increasing frequency and approximately as a quadratic function with increasing particle size. Increasing the preloading force leads to a reduction in the abrasive kinetic energy. Besides, the kinetic energy induced by the shock wave has a cliff-like increment at an amplitude of 0.7–0.8 μm. It is revealed that the abrasive kinetic energy is suppressed by the cavitation bubble expansion and collapse at smaller ultrasonic pressure amplitude and surround-wall distance. This research provides a theoretical reference for the modeling of potential defects and material removal on the workpiece surface caused by abrasive motion during polishing, and reduces the trial cost for parameter optimization in actual polishing processing.

Ex uno plures: how to construct high-speed movies of collapsing cavitation bubbles from a single image

The time-resolved visualization of the dynamics of a cavitation bubble usually requires the use of expensive high-speed cameras, which often provide a limited spatial resolution. In the present study, we propose an alternative to these high-speed imaging techniques. The method is based on the recently introduced virtual frame technique, which relates the motion of a monotonic propagating front to the resulting image blur captured on a long-exposure shadowgraph. We use a consumer-level camera to photograph the entire collapse phase of cavitation bubbles. We then demonstrate that both the dynamics of a spherically collapsing bubble and those of a bubble collapsing near a rigid boundary can be accurately reconstructed from this single photograph at a virtual frame rate of up to 2 Mfps on a 24.2 Mpx sensor.

Experimental study on influence of particle shape on shockwave from collapse of cavitation bubble

The bubble dynamics under the influence of particles is an unavoidable issue in many cavitation applications, with a fundamental aspect being the shockwave affected by particles during bubble collapse. In our experiments, the method of spark-induced bubbles was used, while a high-speed camera and a piezoresistive pressure sensor were utilized to investigate how particle shape affects the evolution of shockwaves. Through the high-speed photography, we found that the presence of the particle altered the consistency of the liquid medium around the bubble, which result in the emitting of water hammer shockwave and implosion shockwave respectively during the collapse of the bubble. This stratification effect was closely related to the bubble-particle relative distance φ and particle shape δ. Specifically, when the bubble-particle relative distance φ < 1.34 e-0.10δ, particles disrupted the medium consistency around the bubbles and led to a nonspherical collapse and the consequent stratification of the shockwave. By measuring the stratified shockwave intensity affected by different particle shapes, we found that the stratified shockwave intensity experienced varying degrees of attenuation. Furthermore, as the particle shape δ increased, the attenuation of the particle on shockwave intensity gradually reduced. These new findings hold significant theoretical implications for elucidating cavitation erosion mechanisms in liquid–solid two-phase flows and applications and prevention strategies in liquid–solid two-phase cavitation fields.