Influence of Bubble Deformation on the Signal Characteristics Generated Using an Optical Fiber Gas–Liquid Two-Phase Flow Sensor

The use of optical fiber probe in two-phase flow measurements is very frequently encountered, especially in the applications of chemical engineering and petroleum industries. In this work, the influence of bubble piercing signals caused by bubble deformation is studied experimentally using a laboratory-prepared wedge-shaped fiber probe in a lab-scale gas–liquid flow generator. A three-dimensional simulation model is established to study the influence of bubble deformation on the piercing signals. A theoretical analysis of the characteristics of the pre-signal influenced by the bubble deformations is undertaken for a wide range of different modeled bubble shapes. Combining the experimental and simulation results, a promising analytical method to estimate the bubble shapes by analyzing the characteristics of pre-signals is proposed. The results of this investigation demonstrate that it is possible to estimate the bubble shapes before the fiber probe contacts the bubble surface. The method developed in this investigation is therefore highly promising for reducing errors caused by deformation during the probe piercing process.

Correction to: Complex bubble deformation and break-up dynamics studies using interface capturing approach

The article “Complex bubble deformation and break-up dynamics studies using interface capturing approach” written by Yuqiao Fan, Jun Fang, and Igor Bolotnov, was originally published electronically on the publisher’s internet portal (currently SpringerLink) on 18 July 2020 without open access. After publication in Volume 3, Issue 3, page 139–151, the author(s) decided to opt for Open Choice and to make the article an open access publication. Therefore, the copyright of the article has been changed to © The Author(s) 2021 and the article is forthwith distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, duplication, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Deformation characteristics of a single bubble in immiscible fluids

In order to investigate characteristics of bubble deformation in immiscible fluids, the bubble shape change during the interface and the relationship between aspect ratio(E) and dimensionless number of forces is obtained. A three-dimensional model is established and the free-floating behavior of a single bubble in immiscible fluids is numerically simulated by phase-field method. The simulation results are in good agreement with experimental results. The research shows that, in the lower liquid, the relationship between E and We, Ta, Re is distributed between two intersecting lines. In the upper liquid, the relationship between E and We, Ta, Re is distributed between two parallel lines. Comparing the bubble deformation and the influence of the forces. Compared with gravity, the inertial force plays a leading role in the bubble shape in the lower liquid and upper liquid. Compared with the viscous force, the surface tension dominates the bubble shape in the lower liquid.

Lattice Boltzmann Model Simulation of Bubble Deformation and Breakup Induced by Micro-Scale Couette Flow

Understanding the morphology of transformation of a single bubble immersed in a liquid undergoing a shear flow is essential in predicting bubble deformation and breakup phenomena commonly found in applications involving complex liquid-gas multiphase flow. In this study, the deformation and breakup of a single bubble released in a fully developed laminar Couette flow in a micro-scale domain are evaluated under different spanwise positions, as well as under different initial diameters. The simulation is carried out using a multiphase Shan-Chen Lattice Boltzmann Model (SC-LBM). The transition between deformation and breakup experienced by the bubble is described under different Capillary (Ca) numbers, viscosity ratios and relative initial spanwise positions with respect to the channel centreline. A critical Ca number, Cac = 0.31, was found at the onset of breakup, with bubble centroid location varying as a function of the remaining parameters. The results obtained with the SC-LBM are in excellent agreement with those published in the literature.

Visualization of Coalescence of Multiple Small Bubbles with Closed B-Spline Curve

The smoothness of surface shape is one of the key issues to simulate coalescence of underwater bubbles. In this paper, B-spline closed curve is used to realize the visual simulation of multibubble coalescence. The main idea of the proposed algorithm is to construct a continuous bubble deformation which is guided by the normal direction of each control point and weighted by the distance from the point to the geometry center of the contour. The advantages of this algorithm include the smoothness of the bubble contour in the processing of deformation and the randomness of dynamic process and coalescence process. Experiment results show that the simulation algorithm works well and can be used in 3D computer games and animations.

Numerical Simulation of Breathing Mode Oscillation on Bubble Detachment

When a bubble detaches from a nozzle immersed in water, a sound is emitted owing to the detachment. The bubble deformation and sound emission generated after detachment has been investigated in many studies, in which the breathing mode with a natural frequency was discussed based on the dynamics of the interface between the air and water. In this study, the deformation of a bubble was observed, and the sound emitted upon detachment was measured experimentally. To analyze the bubble deformation process, a computational fluid dynamics (CFD) simulation was conducted using the volume of fluid (VOF) method to predict the sound emission. In the analysis, the deformation behavior, the oscillation frequencies, sound pressure, and radius variation were discussed by comparing the numerical and experimental data. Furthermore, the natural frequency and low frequency vibrations were discussed based on the interference between the detached bubbles and the air column vibrations.

Numerical simulation of bubble deformation in various velocity profiles across a conduit

<p>Tube pumice is characterized by aligned highly elongated bubbles and is a common product of explosive silicic eruptions. The relative abundance of tube pumice and non-tube pumice in the stratigraphy has been interpreted as resulting from temporal and spatial variations in a conduit flow. Therefore, understanding the formation mechanism of tube pumice is valuable, but still debated. Most previous studies interpret tube pumice forming from simple shear deformation, assuming a parabolic velocity profile across a conduit. However, simple shear cannot explain the observation that tube pumice is rare in plinian falls but frequent in ignimbrites (interpreted to have wider vents).</p><p>In this study, we combine a bubble deformation model with a quasi-two-dimensional steady conduit flow model. A bubble is deformed by the velocity gradient while moving within the conduit flow. The conduit flow model is calculated for the 1.8 ka Taupo plinian eruption, which produced a high proportion of tube pumice in the ignimbrite phase. In this abstract, we explain results from two rheological models showing distinct velocity profiles. In the Newtonian isothermal fluid, the velocity profile across the conduit becomes parabolic. In a fluid that allows viscous heating, the temperature near the conduit wall rises up sharply, leading to a strong reduction in viscosity, and the velocity profile changes from a parabolic shape to a plug-like shape. The parabolic velocity profile produces highly elongated bubbles mainly by simple shear, while the plug-like velocity profile is dominated by pure shear and accumulates less strain to elongate bubbles. The bubble shape at the fragmentation surface depends significantly on the velocity profile and its change along the conduit.</p><p>We also conduct a quantitative and statistical bubble shape analysis of pumice erupted at Taupo volcano. It shows that the plinian pumices have a single peak in the bubble shape distribution, while the ignimbrite pumices have a broad distribution and contain highly elongated bubbles. The comparison of the distribution of pumice textures with the simulation results suggests that the velocity profile of the plinian phase is close to a plug-like shape. We also calculate bubble deformation for the Taupo ignimbrite eruption, using the viscous-heating model. We model a　wider conduit for the ignimbrite phase which leads to lower shear rate around the conduit walls and a higher proportion of the conduit experiencing parabolic flow compared to the plinian phase. This increased proportion of parabolic velocity profile in the conduit can explain a large number of tube pumice in the Taupo ignimbrite.</p>