Bubble Profile Research Articles

Simulation of the Effect of Particle-bubble Size Ratio on the Collapsing Dynamics of a Cavitation Bubble Near a Particle

Abstract The synergistic effect of cavitation bubbles and sediment particles on material damage is a significant problem in fluid machinery. The dynamic behavior of a cavitation bubble near a spherical particle were simulated in this study using the Volume of Fluid (VOF) method. The effects of the particle-bubble size ratio δ on the bubble profiles, the collapse time, the micro-jets and the pressure at the particle surface have been investigated under the conditions of three values of stand-off distance γ. The results show that (1) the bubble collapse time rises as the particle-bubble size ratio δ increases; (2) the peak values of the maximum jet velocity and the maximum pressure exerting on the particle appear at γ = 1.0 and δ = 1.2, which are 165.3 m/s and 10.46 MPa, respectively; (3) the influence on the particle caused by the micro-jets cannot be ignored when the stand-off distance is less than 1.5.

Non-linearities in cosmological bubble wall dynamics

A precise modelling of the dynamics of bubbles nucleated during first-order phase transitions in the early Universe is pivotal for a quantitative determination of various cosmic relics, including the stochastic background of gravitational waves. The equation of motion of the bubble front is affected by the out-of-equilibrium distributions of particle species in the plasma which, in turn, are described by the corresponding Boltzmann equations. In this work we provide a solution to these equations by thoroughly incorporating the non-linearities arising from the population factors. Moreover, our methodology relies on a spectral decomposition that leverages the rotational properties of the collision integral within the Boltzmann equations. This novel approach allows for an efficient and robust computation of both the bubble speed and profile. We also refine our analysis by including the contributions from the electroweak gauge bosons. We find that their impact is dominated by the infrared modes and proves to be non-negligible, contrary to the naive expectations.

Profiles of Static Liquid-Gas Interfaces in Axisymmetric Containers with Different Accelerations.

Second-order perturbation solutions of profiles of bubbles suspended in liquid and liquid-gas interfaces when liquid all sinks in the bottom with different accelerations are derived. Six procedures are developed based on these solutions, and they are divided into two types. One type takes the coordinates of end points of profiles as input, and the other type takes liquid volume or gas volume as input. Numerical simulations are performed with the Volume of Fluid method, and numerical results are in good agreement with the predictions of these procedures. The greater the acceleration, the flatter the bubble until all liquid sinks to the bottom. Effects of acceleration on bubble shape must be considered; otherwise, it will cause a volume prediction error of up to 10%. When all liquid sinks to the bottom, predictions of liquid volume with the same liquid meniscus height as inputs differ considerably for different accelerations. The most significant change in liquid volume occurs when the bond number Bo ≪ 1. Effects of acceleration and liquid contact angle on the liquid-gas interfaces must be considered when evaluating liquid residue. These findings should be quite helpful for liquid residue measurement and fine management in spacecraft.

Bubble nucleation in the two-flavor quark-meson model* *Supported in part by the National Natural Science Foundation of China (NSFC) (11675048)

We investigate the dynamics of a first-order quark-hadron transition via homogeneous thermal nucleation in the two-flavor quark-meson model. The contribution of the fermionic vacuum loop in the effective thermodynamics potential and phase diagram, together with the location of the critical endpoint (CEP), is obtained in the temperature and chemical potential plane. For weak and strong first-order phase transitions, by taking the temperature as a variable, the critical bubble profiles, evolutions of the surface tension, and saddle-point action in the presence of a nucleation bubble are numerically calculated in detail when fixing the chemical potentials at and . Our results show that the system could be trapped in the metastable state for a long time as long as the temperature is between the metastable region characterized by the up and low spinodal lines. Moreover, the surface tension at criticality will rise to approximately when the chemical potential is very high. Such a small surface tension value would favor a mixed phase in the cores of compact stars and may have an important implication in astrophysics.

Gravitational waves, bubble profile, and baryon asymmetry in the complex 2HDM

Gravitational waves, bubble profile, and baryon asymmetry in the complex 2HDM

Particle-Bubble Interactions: an Investigation of the Three-Phase Contact Line by Atomic Force Microscopy.

The dynamics of the three-phase contact line during particle-bubble interactions determine the stability of particle-bubble aggregates in flotation. The interaction of particles and sessile gas bubbles can be studied by colloidal probe atomic force microscopy (CP-AFM). This paper demonstrates a method to obtain the contact angle, the position of the three-phase contact line on the particle, and the bubble profile by utilizing the full information contained in AFM force-distance curves, i.e., force and CP-position information as well as the work done to move the three-phase contact line on the CP-particle. The proposed method does not require any assumption of a constant contact angle or a constant opening angle. This is achieved by the combined solution of the particle force balance and an expression for the work required to move the three-phase contact line over the colloid probe. The applicability to AFM force-distance measurements was demonstrated for the interaction of a hydrophobic SiO2 or a hydrophobic Al2O3 colloidal probe particle with sessile gas bubbles having radii between 45 and 80 μm.

Large Eddy Simulation of Bubble Column Bubbly Flow Considering Subgrid‐Scale Turbulent Diffusion Effects and Bubble Oscillation

AbstractThrough Euler/Euler large eddy simulation (LES) modeling, it is demonstrated that turbulent dispersion of bubbles can effectively indicate the impact of turbulent eddies on the bubble dynamics, i.e., the bubble oscillation behavior. This finding builds on previous work using the Euler/Lagrange LES modeling approach and leads to a significant improvement in predicting bubble lateral dispersion. Spatially filtered terms were proposed for the subgrid‐scale (SGS) turbulent dispersion and added mass stress force models, with a modification made to the SGS eddy viscosity to reflect bubble turbulent dispersion and oscillations. The proposed model substantially improves the prediction of bubble volume fraction distribution, bubble and liquid phase velocity profiles, the turbulent kinetic energy spectrum, and mass transfer.

Collision integrals for cosmological phase transitions

The dynamics of the true-vacuum bubbles nucleated during a first-order phase transition is affected by the distribution functions of the particle species in the plasma, driven out-of-equilibrium by the travelling domain wall. An accurate modelling of this phenomenon is relevant for a quantitative description of phase transitions in the early universe and for the determination of the corresponding cosmic relics, such as, among the others, the stochastic background of gravitational waves. We address this problem by developing a new spectral method devised for a fast and reliable computation of the collision integral in the Boltzmann equations. In a scalar singlet extension of the Standard Model chosen as a benchmark scenario, we test our algorithm, determining the bubble speed and profile, and we assess the impact of the out-of-equilibrium dynamics.

Comparison of Vortex Cut and Vortex Ring Models for Toroidal Bubble Dynamics in Underwater Explosions

The jet impact from a collapsing bubble is an important mechanism of structural damage in underwater explosions and cavitation erosion. The Boundary Integral Method (BIM) is widely used to simulate nonspherical bubble dynamic behaviors due to its high accuracy and efficiency. However, conventional BIM cannot simulate toroidal bubble dynamics, as the flow field transforms from single-connected into double-connected. To overcome this problem, vortex cut and vortex ring models can be used to handle the discontinuous potential on the toroidal bubble surface. In this work, we compare these two models applied to toroidal bubble dynamics in a free field and near a rigid wall in terms of bubble profile, bubble gas pressure, and dynamic pressure induced by the bubble, etc. Our results show that the two models produce comparable outcomes with a sufficient number of nodes in each. In the axisymmetric case, the vortex cut model is more efficient than the vortex ring model. Moreover, we found that both models improve in self-consistency as the number of bubble surface elements (N) increases, with N=300 representing an optimal value. Our findings provide insights into the numerical study of toroidal bubble dynamics, which can enhance the selection and application of numerical models in research and engineering applications.

Morphological Analysis of a Collapsing Cavitation Bubble near a Solid Wall with Complex Geometry

The interaction mechanism between the cavitation bubble and a solid wall is a basic problem in bubble collapse prevention and application. In particular, when bubble collapse occurs near solid walls with arbitrarily complex geometries, it is difficult to efficiently establish a model and quantitatively explore the interaction mechanism between bubbles and solid walls. Based on the advantages of the lattice Boltzmann method, a model for cavitation bubble collapse close to a solid wall was established using the pseudopotential multi-relaxation-time lattice Boltzmann model. Solid walls with arbitrarily complex geometries were introduced in the computational domain, and the fractal dimension was used to quantify the complexity of the solid wall. Furthermore, owing to the lack of periodicity, symmetry, spatial uniformity and obvious correlation in this process, the Minkowski functionals-based morphological analysis method was introduced to quantitatively describe the temporal evolution of collapsing bubble profiles and acquire effective information from the process. The interaction mechanism between the bubble and solid wall was investigated using evolutions of physical fields. In addition, the influences of the solid walls’ surface conditions and the position parameter on collapsing bubbles were discussed. These achievements provide an efficient tool for quantifying the morphological changes of the collapsing bubble.

Baryogenesis and gravitational waves in the Zee–Babu model

To explain the matter-antimatter asymmetry in the Zee–Babu (ZB) model, the sphaleron process in the baryogenesis scenario is calculated. It always satisfies the de-coupling condition and the strength of phase transition (S) is always greater than 1 in the presence of triggers other than that in the Standard Model, which are singly (h^{pm }) and doubly (k^{pm pm }) charged scalar bosons. Sphaleron energies are in the range of 5-10 TeV, in calculation with bubble profiles containing free parameters and assuming nuclear bubbles of h^{pm } and k^{pm pm } are very small. We tested the scaling law of sphaleron again with an average error of 10%. When the temperature is close to the critical one (T_c), the density of nuclear bubble is produced very large and decreases as the temperature decreases. The key parameter is alpha which results in the gravitational wave density parameter (Omega h^2) in the range of 10^{-14} to 10^{-12} when beta /H^*=22.5, this is not enough to detect gravitational waves from electroweak phase transition (EWPT) according to the present LISA data but may be detected in the future. As the larger strength of phase transition is, the more alpha increases (this increase is almost linear with S), the larger the gravitational wave density parameter is. Also in the context of considering the generation of gravitational waves, in the ZB model we calculated alpha sim text {a few} times 10^{-2}ll 1, so rigorously conclude that the EWPT is not strong even though S>1. We also suggest that, for a model with a lot of extra scalar particles and particles which play a role in mass generation, the stronger the EWPT process and the larger Omega h^2 can be.

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.

Holographic bubbles with Jecco: expanding, collapsing and critical

Cosmological phase transitions can proceed via the nucleation of bubbles that subsequently expand and collide. The resulting gravitational wave spectrum depends crucially on the properties of these bubbles. We extend our previous holographic work on planar bubbles to cylindrical bubbles in a strongly-coupled, non-Abelian, four-dimensional gauge theory. This extension brings about two new physical properties. First, the existence of a critical bubble, which we determine. Second, the bubble profile at late times exhibits a richer self-similar structure, which we verify. These results require a new 3+1 evolution code called Jecco that solves the Einstein equations in the characteristic formulation in asymptotically AdS spaces. Jecco is written in the Julia programming language and is freely available. We present an outline of the code and the tests performed to assess its robustness and performance.

Fate of the false vacuum in string-inspired nonlocal field theory

In this article, we study Coleman bounce in weakly nonlocal theories which are motivated from string field theory. The kinetic term is extended via an infinite series of high-order derivatives, which comes into play at an energy scale M, without introducing any new states or ghosts in the mass spectrum. We calculate the bubble nucleation in thin-wall approximation, treating the system in semi-classical manner. We find that the effect of nonlocal scale M in the theory is to suppress the vacuum tunneling rate from false to true vacuum compared to the standard local bouncing scenario. Likewise, we show that as we move further away from the bubble wall, the effects of nonlocality gets reduced and this suppression is significant only around the wall of the nucleated bubble. From our investigations, we conclude that the main effect is due to the fact that the nonlocality smears the solution of the local bubble profile. However, the energy of the bubble wall remains unaffected by the microscopic nonlocal behavior of the theory in the thin-wall approximation. We also discuss the cases for Lee-Wick theories and applications of our result to cosmology.

A Multistate Adsorption Model for the Characterization of C13DMPO Adsorption Layers at the Aqueous Solution/Air Interface.

Experimental data for tridecyl dimethyl phosphine oxide (C13DMPO) adsorption layers at the water/air interface, including equilibrium surface tension and surface dilational viscoelasticity, are measured by bubble and drop profile analysis tensiometry at different solution concentrations and surface area oscillation frequencies. The results are used to assess the applicability of a multistate model with more than two possible adsorption states. For the experiments with single drops, the depletion of surfactant molecules due to adsorption at the drop surface is taken into account. For the assessment, the same set of model parameters is used for the description of all obtained experimental dependencies. The agreement between the proposed model and the experimental data shows that for the nonionic surfactant C13DMPO, the description of the adsorption layer behavior by three adsorption states is superior to that with only two adsorption states.

A Multistate Adsorption Model for the Adsorption of C14EO4 and C14EO8 at the Solution/Air Interface

The dynamic and equilibrium properties of adsorption layers of poly (oxyethylene) alkyl ether (CnEOm) can be well described by the reorientation model. In its classical version, it assumes two adsorption states; however, there are obviously surfactants that can adsorb in more than two possible conformations. The experimental data for C14EO4 and C14EO8 (dynamic and equilibrium surface tensions and surface dilational visco-elasticity as measured by bubble profile analysis tensiometry) are used to verify if a reorientation model with more than two possible adsorption states can better describe the complete set data of CnEOm adsorption layers at the water/air interface. The proposed refined theoretical model allows s different states of the adsorbing molecules at the interface. The comparison between the model and experiment demonstrates that, for C14EO4, the assumption of s = 5 adsorption states provides a much better agreement than for s = 2, while for C14EO8, a number of s = 10 adsorption states allows an optimum data description.

The ‘COVID’ crash of the 2020 U.S. Stock market

We employed the log-periodic power law singularity (LPPLS) methodology to systematically investigate the 2020 stock market crash in the U.S. equities sectors with different levels of total market capitalizations through four major U.S. stock market indexes, including the Wilshire 5000 Total Market index, the S&P 500 index, the S&P MidCap 400 index, and the Russell 2000 index, representing the stocks overall, the large capitalization stocks, the middle capitalization stocks and the small capitalization stocks, respectively. During the 2020 U.S. stock market crash, all four indexes lost more than a third of their values within five weeks, while both the middle capitalization stocks and the small capitalization stocks have suffered much greater losses than the large capitalization stocks and stocks overall. Our results indicate that the price trajectories of these four stock market indexes prior to the 2020 stock market crash have clearly featured the obvious LPPLS bubble pattern and were indeed in a positive bubble regime. Contrary to the popular belief that the 2020 US stock market crash was mainly due to the COVID-19 pandemic, we have shown that COVID merely served as sparks and the 2020 U.S. stock market crash had stemmed from the increasingly systemic instability of the stock market itself. We also performed the complementary post-mortem analysis of the 2020 U.S. stock market crash. Our analyses indicate that the probability density distributions of the critical time for these four indexes are positively skewed; the 2020 U.S. stock market crash originated from a bubble that had begun to form as early as September 2018; and the bubble profiles for stocks with different levels of total market capitalizations have distinct temporal patterns. This study not only sheds new light on the makings of the 2020 U.S. stock market crash but also creates a novel pipeline for future real-time crash detection and mechanism dissection of any financial market and/or economic index.

Effect of the Inlet Boundary Conditions on the Flow over Complex Terrain Using Large Eddy Simulation

For large eddy simulation, it is critical to choose the suitable turbulent inlet boundary condition as it significantly affects the calculated flow field. In this paper, the effect of different inlet boundary conditions, including random method (RAND), Lund method, and divergence-free synthetic eddies method (DFSEM), on the flow in a channel with a hump are investigated through large-eddy simulation. The simulation results are further compared with experimental data. It has been found that turbulence is nearly fully developed in the case based on the Lund method, not fully developed in the case based on DFSEM, and not developed in the case based on the RAND method. In the flow region before the hump, mean velocity profiles in the case applying the Lund method gradually fit the law of the wall as the main flow moves towards the hump, but the simulation results based on the RAND and DFSEM methods cannot fit the wall function. In the flow region after the hump, cases applying Lund and DFSEM methods could relative precisely predict the size of turbulent bubble and turbulent statistics profiles. Meanwhile, the case based on the RAND method cannot capture the positions of flow separation and re-attachment point and overestimates the turbulent bubble size. From this research, it could be found that different turbulent inflow generation methods have a manifested impact on the flow separation and re-attachment after the hump. If the coherent turbulence is maintained in the approach flow, even though turbulent intensity is not large enough, the simulation can still predict the flow separation and turbulent bubble size relative precisely.

Thermodynamics, Kinetics and Dilational Visco-Elasticity of Adsorbed CnEOm Layers at the Aqueous Solution/Air Interface

The adsorption behaviour of linear poly(oxyethylene) alkyl ether (CnEOm) is best described by a reorientation model. Based on a complete set of experimental data, including the adsorption kinetics, the equilibrium surface tension isotherm and the surface dilational visco-elasticity, the thermodynamic and kinetic adsorption parameters for some CnEOm at the water/air interface were determined. For the study, six CnEOm surfactants were selected (n = 10, 12 and 14 and m = 4, 5 and 8) and were studied by bubble profile analysis and maximum bubble pressure tensiometry. A refined theoretical model based on a reorientation-adsorption model combined with a diffusion-controlled adsorption kinetics and exchange of matter allowed us to calculate the surface layer composition by adsorbing molecules in different orientations. It turns out that at larger surface coverage, the adsorption rate decreases, i.e., the apparent diffusion coefficients are smaller. This deceleration can be explained by the transition of molecules adsorbed in a state of larger molar surface area into a state with smaller molar surface area.

Bubble dynamics in a strong first-order quark-hadron transition * *Supported in part by National Natural Science Foundation of China (NSFC) (11675048)

We investigate the dynamics of a strong first-order quark-hadron transition driven by cubic interactions via homogeneous bubble nucleation in the Friedberg-Lee model. The one-loop effective thermodynamic potential of the model and the critical bubble profiles have been calculated at different temperatures and chemical potentials. By taking the temperature and the chemical potential as variables, the evolutions of the surface tension, the typical radius of the critical bubble, and the shift in the coarse-grained free energy in the presence of a nucleation bubble are obtained, and the limit on the reliability of the thin-wall approximation is also addressed accordingly. Our results are compared to those obtained for a weak first-order quark-hadron phase transition; in particular, the spinodal decomposition is relevant.