Bubble Position Research Articles

On the focusing effect and interfacial evolution of incident shock waves impinging on double-layer nested heavy gas bubbles

A detailed numerical study about the planar incident shock wave impinging on heavy bubbles with different components and nested structures was conducted. Results show that the shock wave convergence occurs when the incident shock wave impinging on the pure SF6 bubble or CO2-SF6 nested bubbles, which triggers the shock wave focusing and obtains a high transient pressure. Changing the nested position and radius of the SF6 bubble in CO2-SF6 nested bubbles will change the interactional time and relative position of waves to affect the shock wave focusing time and peak pressure. Specifically, the shock wave focusing effect is enhanced, and the peak pressure is increased when the inner bubble is drifted downstream, high density, and larger sized. Thus, the later the shock wave focusing occurs, the higher the transient maximum pressure. The shock wave focusing process of double-layer nested bubbles is presented as follows: the new small shock wave (SS) formed by the intersection between the incident transmitted shock wave and the transmitted shock wave and another new shock wave formed by the collision of diffracted transmitted shock waves move in opposite directions to squeeze the undisturbed region and finally produce a high instantaneous pressure, where SS plays a major role in shock wave focusing. Further, the greater the intensity and velocity of focusing shock waves, the stronger the focusing effect and the higher the transient pressure.

Influence of distribution parameters on acoustic radiation from bubble clusters

Cavitation noise is the major noise in underwater, and the study of acoustic radiation from bubble clusters is the primary means to reveal the mechanism of cavitation noise. In this study, direct numerical simulation (DNS) of bubble clusters with volume fractions of 20–40 % with different bubble sizes and bubble position distributions are performed, and the far-field sound pressure is calculated using the Ffowcs Williams–Hawkings (FW-H) method. Then, we compare the collapse and acoustic radiation of bubble clusters with equivalent bubble. The results show that the collapse times of bubble clusters at the same volume fraction are identical and close to equivalent bubble, despite the different bubble sizes and positions in the bubble cluster. Further, in terms of acoustic radiation, the layered arrangement of bubble positions results in bubble clusters exhibiting layer-by-layer collapse and emitting multiple sound pressure pulses. In contrast, a random arrangement of bubble positions lacks this feature, resulting in the collapse of the bubble cluster without a layered phenomenon and radiating only a single primary sound pulse, which is consistent with the equivalent bubble. Additionally, the distribution of bubble sizes in the bubble cluster has almost no effect on the acoustic radiation of the bubble cluster. Notably, when the volumetric fraction exceeds 25 %, the sound pressure levels of bubble clusters with different distributions in the frequency domain are nearly identical, with differences from the equivalent bubble within 5 dB.

Research of Bubble Breakup and Influencing Factors in Flotation Machine

As the core factor of flotation, bubbles have an important effect on flotation. The rotor speed, initial gas parameters and impeller structure of the flotation machine will affect the formation and movement of bubbles. It is very important to study the influence mechanism of operating parameters of flotation machine on the bubble breakup process for flotation machine design and structure optimization. This paper takes KYF-0.2m<sup>3</sup> flotation machine as the research object, establishes a single bubble analysis model, adopts the VOF (Volume of Fluid) method to analyze the influence of different initial positions of bubbles on the bubble breakup behavior, and studies the influence of impeller speed and initial position of bubbles on the bubble breakup. Result show that the breakup of bubbles mainly occurs near the stator region. With the increase of rotational speed of the impeller, the centrifugal force and the disturbance of the convection field will become greater, the time of the bubble breakup become shorter, more bubbles breakup and generate more smaller ones. With the bubble position is closer to the rotating axis of the impeller, the impact of reflow becomes stronger and the bubble breakup effect will be better, and if the bubble initial position closer to the impeller cover, the influence of impeller on the bubbles become greater and the distribution of bubbles will be more uniform.

Boundary Layer Analysis of a Transonic High-Pressure Turbine Vane Using Ultra-Fast-Response Temperature-Sensitive Paint

Abstract The focus of this article is the impact of surface roughness on the boundary layer caused by a 7YSZ thermal barrier coating (TBC). Experimental investigations are conducted on a NGV installed inside the wind tunnel for Straight Cascades Göttingen (EGG). The shape of the vane has been altered in a way that eliminates the influence of TBC's thickness. Therefore, it is expected that only the surface roughness is influencing the location of the separation and boundary layer transition. The transition next to the roughness can also be affected by positive and negative pressure gradients, separation, and interacting shocks. The impact of TBC on the turbulent wedges' appearance, separation bubble's position and length, and transition location is examined in this study. This research, combined with prior investigations, provides a comprehensive understanding of a turbine vane's aerothermodynamics. To investigate unsteady flow phenomena on a TBC-coated NGV, ultra-fast-response temperature-sensitive paint (iTSP) is utilized. This dataset will serve as a reference point for developing new turbine vane designs that include TBC and extensive cooling. Furthermore, the findings will be employed as a benchmark for improving numerical models.

Bubble departure and sliding in high-pressure flow boiling of water

Bubble growth, departure and sliding in low-pressure flow boiling has received considerable attention in the past. However, most applications of boiling heat transfer rely on high-pressure flow boiling, for which very little is known, as experimental data are scarce and very difficult to obtain. In this work, we conduct an experiment using high-resolution optical techniques. By combining backlit shadowgraphy and phase-detection imaging, we track bubble shape and physical footprint with high spatial ( $6\,\mathrm {\mu }{\rm m}$ ) and temporal ( $33\,\mathrm {\mu }{\rm s}$ ) resolutions, as well as bubble size and position as bubbles nucleate and slide on top of the heated surface. We show that at pressures above 1 MPa bubbles retain a spherical shape throughout the growth and sliding process. We analytically derive non-dimensional numbers to correlate bubble velocity and liquid velocity throughout the turbulent boundary layer and predict the sliding of bubbles on the surface, solely from physical properties and the bubble growth rate. We also show that these non-dimensional solutions can be leveraged to formulate elementary criteria that predict the effect of pressure and flow rate on bubble departure diameter and growth time.

Dynamic response of He bubbles in Fe9Cr1.5W0.4Si F/M steel under in-situ stepwise nanocompression

Inert-gas bubbles in metals have attracted great attention due to their fundamental role in swelling and degradation of materials. Studies of bubble behavior can provide valuable insights for developing advanced materials. Although extensive research has been conducted on bubble behavior under irradiation or thermal conditions, there is still a lack of investigation under both stress and temperature conditions. In this work, in-situ uniaxial compression tests were performed on helium-bubbled Fe9Cr1.5W0.4Si F/M steel using transmission electron microscopy at 923 K to investigate the responses of bubbles with increasing strain. The results revealed a series of bubble responses, including frequent annihilation, occasional coalescence, and a "forced" coalescence achieved by connecting multiple bubbles under high strain. These responses relied on bubble migration and interaction, influenced by the factors such as the He-V ratio, relative bubble position, and sink effect. Furthermore, the migration mechanism of compressed bubbles at high temperatures is considered to be a combination of surface diffusion induced by thermal gradient and volume diffusion induced by stress gradient. These two mechanisms are expected to compete with each other in different temperature and stress. These findings offer crucial experimental insights into the behavior of bubbles in solids exposed to stress and thermal conditions.

Investigation on laser-induced bubble collapse among triple particles based on high-frame-rate photography and the Kelvin impulse model

In fluid machinery, the concurrent presence of cavitation bubbles and particle clusters leads to considerably damage to material surfaces. This study investigates the dynamics of a bubble situated among triple particles based on the Kelvin impulse model and high-frame-rate photography, focusing on the impact of the dimensionless distance of particles and the bubble size. Specifically, the jet, bubble motion, and bubble interface evolution characteristics are quantitatively evaluated. The following conclusions are obtained: (1) The collapse shapes of the bubble can be divided into three typical cases: equilateral triangle shape, isosceles triangle shape, and arcuate shape. (2) Among the triple particles, four zero-Kelvin-impulse locations are present, around which the jet direction is extremely sensitive to the bubble initial position. As the bubble initial position moves along the central line, the bubble motion direction dramatically changes during its collapse. (3) The relative position of bubble and particles is the key parameter that affects the bubble dynamics. As the bubble–particle distance decreases, the non-uniformity of bubble collapse morphology and the bubble motion distance will become more significant.

Machine Learning Assisted Experimental Characterization of Bubble Dynamics in Gas-Solid Fluidized Beds.

This study introduces a machine learning (ML)-assisted image segmentation method for automatic bubble identification in gas-solid quasi-2D fluidized beds, offering enhanced accuracy in bubble recognition. Binary images are segmented by the ML method, and an in-house Lagrangian tracking technique is developed to track bubble evolution. The ML-assisted segmentation method requires few training data, achieves an accuracy of 98.75%, and allows for filtering out common sources of uncertainty in hydrodynamics, such as varying illumination conditions and out-of-focus regions, thus providing an efficient tool to study bubbling in a standard, consistent, and repeatable manner. In this work, the ML-assisted methodology is tested in a particularly challenging case: structured oscillating fluidized beds, where the spatial and time evolution of the bubble position, velocity, and shape are characteristics of the nucleation-propagation-rupture cycle. The new method is validated across various operational conditions and particle sizes, demonstrating versatility and effectiveness. It shows the ability to capture challenging bubbling dynamics and subtle changes in velocity and size distributions observed in beds of varying particle size. New characteristic features of oscillating beds are identified, including the effect of frequency and particle size on the bubble morphology, aspect, and shape factors and their relationship with the stability of the flow, quantified through the rate of coalescence and splitting events. This type of combination of classic analysis with the application of the ML assisted techniques provides a powerful tool to improve standardization and address the reproducibility of hydrodynamic studies, with the potential to be extended from gas-solid fluidization to other multiphase flow systems.

Wall confinement effects on the dynamics of cavitation bubbles in thin tubes

Cavitation is a common phenomenon in nature and has numerous applications. In contrast to a cavitation bubble in a free domain, a cavitation bubble in a thin tube is restricted by the tube wall, which is expected to significantly affect bubble evolution, but its mechanism is still unclear. In this study, the dynamics of a cavitation bubble in a thin circular tube is studied by numerical simulation, focusing on the confinement effects of the tube. The results show that besides affecting the size and lifetime of the bubble, the confinement effects of the tube lead to the generation of counter jets and a ring jet during the contraction process of the bubble, and the curvature of the two counter jets determines the ring jet's peak velocity. When the bubble deviates from the midpoint of the tube in the axial direction, the two sides of the bubble along the axial direction show asymmetric behaviors, which results in the bubble migrating toward the midpoint. The tube diameter, tube length, liquid viscosity, and initial bubble position can significantly influence the degree of confinement effects, which can be characterized by the variations of several key indicators, such as bubble size, lifetime, degree of deformation, counter jet velocity, ring jet velocity, and axial migration of the bubble.

Bubble tracking method based on Kuhn-Munkres algorithm for boiling two-phase flow study

The study of bubble dynamics is important in various engineering applications as it can provide a fundamental understanding of the bubbly flow behavior. This paper presents a novel method for tracking bubble trajectories and classifying bubble behaviors, including formation, extinction, continuous movement, fragmentation, and coalescence. The method is based on the theory of perfect matching in bipartite graphs. By establishing the perfect matching between bubbles identified at adjacent time instants, judging the continuity of bubble motion, and simply calculating the number of bubbles in the neighbor of matching bubbles at adjacent time instants, the method can deal with the challenging situation where the bubble position and volume significantly change between two adjacent time instants. The method is validated in a simulated vertical pipe boiling flow, showing that the tracking accuracy is 100% and classification accuracies for continuous movement, fragmentation, and coalescence events are estimated to be larger than 90% in a wide range of time steps between two adjacent time instants.

The influence of an anticline structure on ambient noise spectral anomalies at an underground gas storage

SUMMARY The purpose of this study is to investigate the seismic ambient noise spectral anomalies that occur near gas reservoirs. These anomalies involve a significant spectral amplification of the vertical component for frequencies generally between 1.5 and 4 Hz and have been reported at various hydrocarbon sites worldwide. There are differing views on the mechanisms responsible for these anomalies. The guideline for this study is that many hydrocarbon reservoirs share a common geological feature: an anticline structure. It appears to cause site effects that influence the amplitude of the ambient noise wavefield. This research examines a dense real data set of ambient noise recorded at the Chémery underground gas storage site in France. The analysis identifies stable spectral anomalies between 1.2 and 2.4 Hz that are correlated to the position of the anticline structure, which also corresponds to the position of the gas bubble. We use a beamforming technique to study the composition and the origin of the ambient noise, and show that the variations of the spectral anomalies over time are correlated to changes in the source wavefield. Finally, we perform numerical simulations of Rayleigh wave propagation within a realistic 3-D velocity model of the Chémery site, while using source distributions directly extracted from real data analysis. The comparison of the simulated anomalies with real data yields a satisfactory qualitative fit. We conclude that the fundamental-mode Rayleigh wave site effect on the anticline is the main mechanism of the spectral anomaly.

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.

Investigation of the influence of different liquid temperatures on the dynamics of long-pulse laser-induced cavitation bubbles

Long-Pulse Laser-induced cavitation bubbles have been identified to hold significant applications in various fields, such as industry and medicine. In this study, the dynamics of cavitation bubbles, induced by a 2.94 μm wavelength Er:YAG laser with an energy of 20 ±1 mJ and transmitted via sapphire fiber optics into distilled water at different temperatures, were investigated. The adiabatic expansion theory was utilized to predict the maximum length (Lmax) and the maximum width (Wmax) of the cavitation bubbles at different liquid temperatures. Excellent alignment was observed between the theoretical predictions and the experimental data. Using this theory, the local overheated liquid temperature was deduced to be ∼180 °C during the formation of cavitation bubbles. It was found that as the liquid temperature increased, the collapse position of the cavitation bubbles, relative to the normalized distance (γ) from the fiber end face, decreased. This study reveals the importance of considering the potential risk of damage to fiber optics from the shockwaves and microjet streams generated by cavitation bubbles in high-temperature conditions.

Dynamic behaviors of a bubble near a rectangular wall with a bulge

In this paper, the cavitation bubble dynamics near a rectangular wall with a bulge are theoretically investigated. High-speed photography is employed to provide experimental verification of the theoretical results. Through a series of conformal transformations and the image method, the analytical description of how this complex wall configuration affects the bubble is shown to be equivalent to the superposition of eight virtual bubbles. The physical meaning of the eight virtual bubbles can be divided into four groups, corresponding to the influence of the left wall, the bottom wall, the angle formed by the two flat walls, and the bulge. The influence of the bulge on the liquid velocity distribution, as well as the intensity and direction of the Kelvin impulse exerted on the bubble, is explored for cases in which the bubble is located at symmetric and asymmetric positions. The main findings are given as follows: During the bubble collapse, a high-velocity area of the liquid exists to the side of the bubble farthest from the bulge, and three stagnation points with three low-velocity areas appear on the bulge surface. The bulge mainly influences the impulse intensity when the bubble is located near the symmetric position. The existence of the bulge causes the impulse angle to attain a minimum as the distance between the bubble and the bulge increases. For a larger bulge radius, the changes in the impulse angle become more complicated as the bubble position angle increases.

Jetting bubbles observed by x-ray holography at a free-electron laser: internal structure and the effect of non-axisymmetric boundary conditions

In this work, we study the jetting dynamics of individual cavitation bubbles using x-ray holographic imaging and high-speed optical shadowgraphy. The bubbles are induced by a focused infrared laser pulse in water near the surface of a flat, circular glass plate, and later probed with ultrashort x-ray pulses produced by an x-ray free-electron laser (XFEL). The holographic imaging can reveal essential information of the bubble interior that would otherwise not be accessible in the optical regime due to obscuration or diffraction. The influence of asymmetric boundary conditions on the jet’s characteristics is analysed for cases where the axial symmetry is perturbed and curved liquid filaments can form inside the cavity. The x-ray images demonstrate that when oblique jets impact the rigid boundary, they produce a non-axisymmetric splash which grows from a moving stagnation point. Additionally, the images reveal the formation of complex gas/liquid structures inside the jetting bubbles that are invisible to standard optical microscopy. The experimental results are analysed with the assistance of full three-dimensional numerical simulations of the Navier–Stokes equations in their compressible formulation, which allow a deeper understanding of the distinctive features observed in the x-ray holographic images. In particular, the effects of varying the dimensionless stand-off distances measured from the initial bubble location to the surface of the solid plate and also to its nearest edge are addressed using both experiments and simulations. A relation between the jet tilting angle and the dimensionless bubble position asymmetry is derived. The present study provides new insights into bubble jetting and demonstrates the potential of x-ray holography for future investigations in this field.

Theoretical and experimental investigation of a bubble collapsing near an asymmetric hydrofoil

In the present paper, the restricted cavitation bubble dynamics near an asymmetric Joukowsky hydrofoil are investigated theoretically and experimentally. This investigation employs the conformal transformation, the image method, and the Kelvin impulse model, together with high-speed photographic experiments. The characteristics of bubble collapse deformation and bubble wall movement are analyzed qualitatively and quantitatively, and the spatial distributions of the liquid velocity and Kelvin impulse are revealed by theoretical predictions. The main conclusions include (1) the bubble collapse deformations can be divided into three typical cases: penetrating deformation (mostly occurs when γ<2 with γ defined as the bubble-hydrofoil dimensionless distance), triangular depression (mostly occurs when 2<γ<4), and arc-shaped depression (mostly occurs when γ>4). (2) The impulse acting on the bubble is governed by a point source and a point sink, which is dominant, and the impulse is inversely correlated with the bubble-hydrofoil distance, which corresponds to the experimental results. (3) The Kelvin impulse exhibits different distributions at the tail, head, and middle regions of the hydrofoil, and the impulse angle remains basically unchanged in the concave region of the asymmetric hydrofoils (i.e., the range of 240°<θz<350° with θz defined as the bubble position angle).

Measurement of Bubble Size Distribution and Generation Position of Bubbles Generated during Smelting Reduction of Iron Oxide-containing Slag

Measurement of Bubble Size Distribution and Generation Position of Bubbles Generated during Smelting Reduction of Iron Oxide-containing Slag

Deep learning-enhanced characterization of bubble dynamics in proton exchange membrane water electrolyzers.

The ever-increasing utility of imaging technology in proton exchange membrane water electrolyzer research raises the demand for rapid and precise image analysis. In particular, for optical video recordings, the challenge primarily lies in the large number of frames that impede the delineation of bubble dynamics with standard methods. In order to address this problem, the present study supports the automation of data analysis to facilitate swift, comprehensive, and measurable insights from captured imagery. We present a deep learning-based framework to perform high-throughput analyses of bubble dynamics using optical images of proton exchange membrane water electrolyzers. Leveraging a relatively small annotated imaging dataset of just 35 images, various configurations of the U-Net architecture were trained to perform bubble segmentation tasks. The best model achieved a precision of 95%, a recall of 78%, and an F1-score of 86% on the validation set. Subsequent to segmentation, the methodology enabled the rapid extraction of parameters such as time-resolved bubble area, size distributions, bubble position probability density, and individual bubble shape analytics. The findings underscore the potential of deep learning to enhance the analysis of polymer electrolyte membrane water electrolyzer imaging, offering a path toward more efficient and informative evaluations in electrochemical research.

Physics-informed neural networks for heat transfer prediction in two-phase flows

This paper presents data-driven simulations of two-phase fluid processes with heat transfer. A Physics-Informed Neural Network (PINN) was applied to capture the behaviour of phase interfaces in two-phase flows and model the hydrodynamics and heat transfer of flow configurations representative of established numerical test cases. The developed PINN approach was trained on simulation data derived from physically based Computational Fluid Dynamics (CFD) simulations with interface capturing. The present study considers fundamental problems, including tracking the rise of a single gas bubble in a denser fluid and exploring the heat transfer in the wake of a bubble rising close to a heated wall. Tracking of a rising bubble phase interface of fluids with disparate properties was performed, revealing a maximum error of only 5.2% at the interface edge and a maximum error of 2.8% at the position of the centre of mass. Inferred (hidden variable) flows are studied in addition to a purely extrapolative inverse isothermal bubble case. When no velocity data was supplied, velocity field predictions remained accurate. Rise of an inferred isothermal bubble with unseen fluid properties was found to produce a maximum mean-squared error of 0.28 and centre of mass error of 1.25%. For the case of the rising bubble with a hot wall, the maximum error in the temperature domain using specified boundary conditions was 6.8%, while the bubble position analysis reveals a maximum positional error of 3.6%. These results demonstrate that PINN is agnostic to geometry and fluid properties when studying the combined effects of convection and buoyancy on two-phase flows for the first time. This work serves as a starting point for PINN in multiphase cases involving heat transfer over a range of geometries. Eventually, PINN will be used in such cases to provide solutions for forward, inverse, and extrapolative cases. Each of which represent a dramatic saving in computational cost compared to traditional CFD.

The impact of transferred air bubble position on clinical pregnancy rate in FET cycles.

We aim to investigate the correlation of the position of the transferred air bubble with the clinical pregnancy rate (PR) in frozen-thawedembryo transfer(FET) cycles. A prospective clinical study was carried out at Reproductive medicine center of West China Second University Hospital between June 2020 and May 2021. 1159 women underwent FET were included in this study. Transabdominal ultrasonographic guidance was used during the transfer procedure. The distance from the air bubble to endometrial cavity fundus（DAF）was measured in the freeze-frame ultrasound immediately after ET. In group DAF ≤3mm, 3-15mm and ≥15mm, the clinical PR in women transferred with cleavage embryos were 33.3% (7/21), 55.0% (153/280), and 31.3% (5/16), respectively, the difference was statistically significant (P＜0.05). Among women transferred with blastocysts, the clinical PR was 63.0% (34/54), 68.5% (485/708) and 55.0% (44/80), respectively, the difference was statistically significant (P＜0.05). In multivariate logistic regression model for clinical PR, the clinical PR was associated with age, embryo quality, number of embryo transferred, and endometrial thickness. DAF was an independent risk factor influencing clinical PR in blastocysts FET cycles rather than in cleavage embryos FET cycles.In conclusion, our results suggested that DAF was associated with the clinical PR and DAF between 3mm and 15mm is the optimal position in blastocysts FET cycles.