Gas Bubble Evolution Research Articles

Undrained shear mechanical behaviors of dense gassy sand

Shallow gas can cause many disasters, and it is reported in many marine engineering constructions. For this, it is imperative to understand the impact of gas on the mechanical behaviors of soil. This study investigated the influence of undrained triaxial compression tests on dense gassy sand commonly encountered in coastal areas. Triaxial tests were performed on specimens with saturations of 100%, 99.8%, 95.9%, and 92.7% under confining pressures of 50 kPa and 200 kPa by a self-developed multi-purpose integrated triaxial apparatus (MITA) for gassy soil. The results are presented in terms of monotonic stress‒strain behavior, volumetric behavior, shear strength, and excess pore water pressure (EPWP). The occurrence of gas bubbles has different effects on loose and dense sands, augmenting the undrained shear strength of loose sand while concurrently diminishing that of dense sand. The deviatoric stress of dense sand increases during shear shrinkage, which is similar to the characteristics of loose sand under the influence of gas bubbles. However, following sand dilation, the effect of gas bubbles on deviatoric stress manifests in an antithetical manner. With elevated gas content, the shear strength of dense sand decreases, accompanied by a deceleration in the development of EPWP and a notable increase in volumetric changes. To this end, a microscopic explanation concerning the deformation and evolution of gas bubbles within sand during the shear process was presented to reveal the macroscopic laws governing the undrained shear attributes of dense gassy sand.

Parameterization of vacancy production rate in phase-field models of fission gas bubble evolution in nuclear fuel

Phase-field modeling has increasingly been used to study microstructural evolution in fission gas bubbles in nuclear fuel to improve understanding of fission gas release. To improve computational efficiency, often only vacancies and gas atoms are included as defect species. In this case, the net effects of vacancy and interstitial production, recombination, and biased sink absorption are included as a net vacancy source, or net vacancy source combined with an effective sink. However, there has been a lack of clarity on what parameter values should be used for these approaches to best match the more complete physical picture that includes interstitials and vacancies. Here, we compare a phase-field model of void growth to analytical models for the source-only and source plus sink approach to gain insight into how the phase-field models can be parameterized effectively. The source-only approach provides greater flexibility to match growth rates determined from the full vacancy-interstitial picture. A strategy was developed for determining the value of the net vacancy source term by comparing to an analytical model that includes vacancy and interstitial production, recombination, and biased sink absorption. This strategy can be used to parameterize phase-field models of fission gas bubble growth.

In-situ observation of hydrogen nanobubbles formation on graphene surface by AFM-SECM

Gas bubble evolution is an important phenomenon in many electrochemical processes and it is highly sensitive to the surface properties. Here we visualize the gas bubble dynamics on the surface of different graphene substrates during hydrogen evolution reaction (HER) using atomic force microscopy combined with scanning electrochemical microscopy. The low overpotential and low surface hydrophobicity of few-layer graphene formed on C-phase SiC causes the uniform distribution of hydrogen nanobubbles, which easily depart from the surface during the reaction. Conversely, the high overpotential and more hydrophobic surface of HOPG induces hydrogen bubbles to linger on the surface for an extended duration, leading to its accumulation and the subsequent formation of microbubbles. This in-situ nanoscale electrochemical mapping of hydrogen bubble dynamics provides new insight into electrocatalytic HER that occurs on non-metal electrodes.

3D Printed Microlattices of Transition Metal/Metal Oxides for Highly Stable and Efficient Water Splitting

AbstractDeveloping affordable electrocatalysts is crucial for driving the sustainable energy transition to green hydrogen. Here, a generalizable method known as polymer infusion additive manufacturing is reported for transforming 3D‐printed photopolymers into core–shell micro lattice electrodes for electrocatalytic water splitting with transition metal/metal oxides/carbon heterointerfaces. The optimized free‐standing architectures integrate Cu/CuOx on carbon (Cu/CuOx/C) microlattices, yielding high electrocatalytic activity (overpotential of 145 mV at 10 mA cm−2 and a Tafel slope of 134 mV dec−1) and excellent durability for the hydrogen evolution reaction (HER) (>100 h), surpassing state‐of‐the‐art Cu foams. Additionally, for the oxygen evolution reaction (OER), Co/CoOx on carbon (Co/CoOx/C) microlattices display exceptional activity with the lowest overpotential (1.40 V to gain 10 mA cm−2) among all reported PGM‐free electrodes. The study explores the gas phase mass‐transport properties of these 3D microlattices via microscopic imaging of bubble evolution, finding that the outstanding electrocatalytic performance and long‐term stability of microlattice electrodes leverages their mesoscale (100–300 µm) pores, providing accessibility of electrolytes, maximizing utilization of active sites, and ensuring rapid evolution of gas bubbles. Thus, a simple but pioneering method is introduced for manufacturing 3D mesostructured electrocatalysts with deep control of liquid and gas phase mass‐transport, enhancing the efficacy of alkaline water electrolysis.

Impact of grain boundary and surface diffusion on predicted fission gas bubble behavior and release in UO2 fuel

In this work, we quantify the impact of grain boundary (GB) and surface diffusion on fission gas bubble evolution and fission gas release in UO2 nuclear fuel using simulations with a hybrid phase field/cluster dynamics model. We begin with a comprehensive literature review of uranium vacancy and xenon atom diffusivity in UO2 through the bulk, along GBs, and along surfaces. In our model we represent fast GB and surface diffusion using a heterogeneous diffusivity that is a function of the order parameters that represent bubbles and grains. We find that the GB diffusivity directly impacts the rate of gas release via GB transport, and that the GB diffusivity is likely below 104 times the lower value from Olander and van Uffelen (2001). We also find that the surface diffusivity impacts bubble coalescence and mobility, and that the bubble surface diffusivity is likely below 10−4 times the value from Zhou and Olander (1984).

Revealing the Impact of Cell Conditioning on PEMWE Catalyst Layer Morphology

Polymer electrolyte membrane (PEM) water electrolysis is a promising green hydrogen generation technology to mitigate the effects of anthropogenic climate change. To achieve stable cell voltages, a conditioning procedure is typically required, where current or voltage cycling is applied until stable performance is achieved. Previous studies have demonstrated that a decrease in voltage occurs within the first few hours of operation [1], but this conditioning period has not been extensively studied for PEM electrolyzers, despite a variety of standard conditioning protocols available for PEM fuel cells in the literature. Previous works additionally suggest that changes in performance may be induced due to structural changes in the anode catalyst layer (CL) caused by large gas bubble evolution during the first few hours of operation [2]. However, to establish and optimize a conditioning procedure for PEMWEs, the specific structural changes caused by conditioning on the anode CL must be elucidated and correlated with the electrochemical performance parameters.In this work, we applied scanning transmission X-ray microscopy (STXM) to PEMWE catalyst layers to reveal pore and ionomer distributions in pristine and conditioned commercial CL samples. Prior to imaging, CL samples were embedded in epoxy and cut to 50 nm thick slices using an ultramicrotome. Using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, Carbon 1s and Fluorine 1s absorption edges were probed to reveal pore and ionomer distributions, respectively. After image acquisition, the image stacks were processed to obtain the ionomer and epoxy spectra to enable spectral fitting and thresholding. Through this analysis, we quantified various morphological properties of catalyst layers (including CL thickness, porosity, pore size distribution, agglomerate distribution, and ionomer content) and compared these properties to those of pristine CLs to explain changes in cell performance. The insights gained from this work will aid in the development of efficient conditioning protocols and identify optimal post-conditioned anode CL morphology to inform the design of next-generation catalyst materials. A. Weiß et al., J Electrochem Soc, 166, F487–F497 (2019).O. Panchenko et al., Mater Today Energy, 16, 100394 (2020).

Effect of grain size on gas bubble evolution in nuclear fuel: Phase-field investigations

Numerous irradiation-induced gas bubbles are created in the nuclear fuel during irradiation, leading to the change of microstructure and the degradation of mechanical and thermal properties. The grain size of fuel is one of the important factors affecting bubble evolution. In current study, we first predict the thermodynamic behaviors of point defects as well as the interplay between vacancy and gas atom in both UO2 and U3Si2 according to ab initio approach. Then, we establish the irradiation-induced bubble phase-field model to investigate the formation and evolution of intra- and inter-granular gas bubbles. The effects of fission rate and temperature on the evolutions of bubble morphologies in UO2 and U3Si2 have been revealed. Especially, a comparison of porosities under different grain sizes is examined and analyzed. To understand the thermal conductivity as functions of grain size and porosity, the heat transfer capability of U3Si2 is evaluated.

NiCo layered double hydroxides/NiFe layered double hydroxides composite (NiCo-LDH/NiFe-LDH) towards efficient oxygen evolution in different water matrices

Engineering robust non-noble metal electrocatalysts towards efficient impure water (e.g., seawater, wastewater) oxidation is a prospective approach to achieve carbon neutrality via accelerating green hydrogen energy development. Herein, a NiCo layered double hydroxides (LDH)/NiFe LDH composite (NiCo-LDH/NiFe-LDH) was developed for oxygen evolution reaction (OER) via a hydrothermal process-electrodeposition method. The optimal NiCo-LDH/NiFe-LDH-30 composite only needed an overpotential (η) of 240 mV to drive 100 mA/cm2 in alkalized freshwater, with a low Tafel slope of 16.6 mV/dec and good stability for over 90 h. Further analyses suggested that the strong interface interaction between NiCo-LDH and NiFe-LDH accelerated the oxygen gas bubble evolution and boosted interfacial charge transfer, and the formed built-in electric field and higher oxidation state species (metal oxyhydroxides) contributed to the high intrinsic catalytic activity. The NiCo-LDH/NiFe-LDH-30 composite also held excellent OER activities in different impure water environments, including alkaline 0.5 M NaCl solution (η100 = 333 mV), alkaline lake water (η100 = 345 mV), and alkaline wastewater treatment plant (WWTP) effluent (η100 = 320 mV). More importantly, the potential effects of Cl− and CO32− in impure water were revealed during the OER process. This work elaborates on the role of built-in electric field and the strong coupling interaction in composite catalysts, which pave the way for the design of cost-effective catalysts with excellent adaptability in different water environments.

Ruthenium‐Induced Activation of Molybdenum‐Cobalt Phosphide for High‐Efficiency Water Splitting

AbstractAdvancing green hydrogen production technologies relies heavily on the development of highly efficient and durable bifunctional catalysts for overall water splitting. Herein, this study reports the ruthenium‐modified hollow cubic molybdenum‐cobalt phosphide (Ru‐MoCoP) as exceptional performance electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Theoretical calculations and experimental results indicate that the incorporation of Ru not only serves as an efficient active site, but also adjusts the electronic structure and improves the reactivity of the original sites, as well as generates more phosphorus vacancies, which improves the electrical conductivity and exposes more active sites. Benefiting from the advantages triggered by the incorporation of Ru mentioned above, the Ru‐MoCoP delivers low overpotentials of 55 and 240 mV at 10 mA cm−2 for HER and OER, respectively. Furthermore, the electrolyzer assembled with Ru‐MoCoP achieves a current density of 50 mA cm−2 at 1.6 V and can be operated stably for 150 h. Notably, the assembled two‐electrode system can be powered by a single commercial AA battery, accompanied with evident gas bubble evolution. This research proposes a promising strategy for the development of highly efficient bifunctional phosphide catalysts, aiming to achieve efficient energy conversion in a wide range of industrial applications.

Solutal Marangoni effect determines bubble dynamics during electrocatalytic hydrogen evolution.

Understanding and manipulating gas bubble evolution during electrochemical water splitting is a crucial strategy for optimizing the electrode/electrolyte/gas bubble interface. Here gas bubble dynamics are investigated during the hydrogen evolution reaction on a well-defined platinum microelectrode by varying the electrolyte composition. We find that the microbubble coalescence efficiency follows the Hofmeister series of anions in the electrolyte. This dependency yields very different types of H2 gas bubble evolution in different electrolytes, ranging from periodic detachment of a single H2 gas bubble in sulfuric acid to aperiodic detachment of small H2 gas bubbles in perchloric acid. Our results indicate that the solutal Marangoni convection, induced by the anion concentration gradient developing during the reaction, plays a critical role at practical current density conditions. The resulting Marangoni force on the H2 gas bubble and the bubble departure diameter therefore depend on how surface tension varies with concentration for different electrolytes. This insight provides new avenues for controlling bubble dynamics during electrochemical gas bubble formation.

Gas Bubble Evolution during ECM Process can be suppressed by Pulse Parameters: High Speed Videographic Observations during Early Stages of Bubble Evolution

The precision in electrochemical machining (ECM) is adversely affected by the generation of gas bubbles due to the inherent electrochemical reactions occurring at the cathode (tool) and anode (workpiece) surface. These gas bubbles are known to cause variations in electrolyte conductivity and lead to uneven dissolution and limit the achievable flatness and surface finish. The demands for precision ECM make it important to investigate the bubble evolution phenomenon. In the prior state of the art, this has been done by means of transparent electrodes and high-speed video observations. The current work involves high-speed video experiments with a specific intention to observe gas bubbles during the early stages of evolution and attempts to address two main research questions: (i) Is it possible to suppress gas bubble evolution in ECM using pulse parameters? (ii) Is it possible to do ECM without gas bubbles? The results reveal that shorter pulse-on times and longer pulse-off times reduce the growth of the concentration boundary layer, thereby suppressing bubble generation. Furthermore, by combining the aforementioned electrical pulse settings with an appropriate flow rate, there is no significant detection of gas bubbles in the experiments conducted here, as can be concluded from the fact that the interelectrode gap (IEG) remains transparent. The industrial applicability-oriented analysis focused on evaluating the final IEG and did not reveal any significant difference due to shorter flow lengths. It is further suggested that by employing high flow rates in combination with shorter pulse-on times, the pulse-off time can be further shortened to raise duty cycles so as to facilitate economic machining without the influence of gas bubbles.

The entrainment and evolution of gas bubbles in bread dough—A review

AbstractBackground and ObjectiveFor control of bread quality to achieve high loaf volume and uniform crumb structure, gas bubble dynamics in dough needs to be better understood throughout different breadmaking processes. The objective of this review was to establish a solid theoretical basis on how flour type, water and salt content, and mixing conditions affected the incorporation, evolution, and stabilization of gas bubbles in a dough.FindingsBubble dynamics including entrainment, disentrainment, break‐up, disproportionation, growth, and coalescence were outlined and their effects on the gas phase of the dough were assessed. The application, advantages, and disadvantages of microscopy, magnetic resonance imaging (MRI) and X‐ray microtomography techniques for qualitatively or quantitatively characterizing the void fraction and bubble size distribution (BSD) in the dough at various stages of the breadmaking process have been discussed.ConclusionsSince the BSD evolution in bread dough is associated with the quality of the resultant products, to devise strategies for improving the product quality, dough formulation, and mixing conditions need to be considered.Significance and NoveltyDue to the obvious challenges of monitoring the fast evolution of BSD in yeasted dough, future research needs to focus on the effects of yeast activity on dough's BSD.

The reconciliation and validation of a combined interatomic potential for the description of Xe in γU-Mo

A U-Mo alloy has been selected as the fuel design for the conversion of high-performance research reactors in the United States. Efforts are ongoing to describe the fuel evolution as a function of time, for a variety of different reactor conditions. The accurate prediction of fuel evolution under irradiation requires the implementation of correct thermodynamic properties into mesoscale and continuum-level fuel performance modeling codes. Molecular dynamics has proven to be a valuable tool to parameterize or inform these higher-length scale models. However, there are currently inaccuracies in the only available U-Mo-Xe potential, which limits the predictive capabilities of molecular dynamics to inform critical phenomena in these fuel systems such as fission gas swelling. This work provides an updated U-Mo-Xe ternary interatomic potential which combines existing potentials in a reconciled format. The validation of the interatomic potential is performed by analyzing the phase stability and vacancy formation energies. Subsequently, Xe solution energies and an equation of state to describe Xe bubbles in U-Mo are calculated, providing 1) evidence of the significant differences between the prior ternary potential and the currently presented potential, and 2) updated data/tools for implementation into mesoscale simulation methodologies to study fission gas bubble evolution.

Global sensitivity analysis of a coupled multiphysics model to predict surface evolution in fusion plasma–surface interactions

We construct a global sensitivity analysis framework for a coupled multiphysics model used to predict the changes in material properties and surface morphology of helium plasma-facing components in future fusion reactors. The model combines the particle dynamics simulator F-TRIDYN, that predicts the helium implantation profile, with the cluster dynamics simulator Xolotl, that predicts the growth and evolution of subsurface helium gas bubbles. In order to keep the sensitivity analysis tractable, we first construct a sparse, high-dimensional polynomial chaos expansion surrogate model for each output quantity of interest, which allows the efficient extraction of sensitivity information. The sensitivity analysis is performed for two problem settings: one for ITER-like conditions, and one that resembles conditions inside the PISCES-A linear plasma device. We present a systematic comparison of important parameters, for both F-TRIDYN and Xolotl in isolation as well as for the coupled model, and discuss the physical interpretation of these results.

Single-size and cluster dynamics modeling of intra-granular fission gas bubbles in UO[formula omitted

We perform simulations of intra-granular fission gas bubble evolution in UO2 using both a relatively simple, computationally inexpensive single-size model and a detailed cluster dynamics model. Simulations encompass 36 experimental cases from 4 different databases, covering various temperature and burnup levels. We systematically compare results from the two models to each other and to post-irradiation experimental data of bubble average size and number density. Overall, the model-to-model comparisons reveal an excellent agreement across the set of simulations. This outcome indicates that, in spite of the underlying assumptions, the single-size model provides a good approximation of the complex physical behavior that is more rigorously described by the cluster dynamics model. Qualitatively, both models reproduce the trends of the experimental data with temperature and burnup correctly. Quantitatively, calculated results are either in good agreement with the data or within errors that appear consistent with the inherent uncertainties. Moreover, for the single-size model, we demonstrate and assess a multiscale approach whereby values for the fission gas atom diffusion coefficient from separate atomistic calculations are used. Systematic comparisons to experimental data point out a credible accuracy of the multiscale model.

Elements of beaked whale anatomy and diving physiology and some hypothetical causes of sonar-related stranding

A number of mass strandings of beaked whales have in recent decades been temporally and spatially coincident with military activities involving the use of midrange sonar. The social behaviour of beaked whales is poorly known, it can be inferred from strandings and some evidence of at-sea sightings. It is believed that some beaked whale species have social organisation at some scale; however most strandings are of individuals, suggesting that they spend at least some part of their life alone. Thus, the occurrence of unusual mass strandings of beaked whales is of particular importance. In contrast to some earlier reports, the most deleterious effect that sonar may have on beaked whales may not be trauma to the auditory system as a direct result of ensonification. Evidence now suggests that the most serious effect is the evolution of gas bubbles in tissues, driven by behaviourally altered dive profiles (e.g. extended surface intervals) or directly from ensonification. It has been predicted that the tissues of beaked whales are supersaturated with nitrogen gas on ascent due to the characteristics of their deep-diving behaviour. The lesions observed in beaked whales that mass stranded in the Canary Islands in 2002 are consistent with, but not diagnostic of, decompression sickness. These lesions included gas and fat emboli and diffuse multiorgan haemorrhage. This review describes what is known about beaked whale anatomy and physiology and discusses mechanisms that may have led to beaked whale mass strandings that were induced by anthropogenic sonar. Beaked whale morphology is illustrated using Cuvier’s beaked whale as the subject of the review. As so little is known about the anatomy and physiology of beaked whales, the morphologies of a relatively well-studied delphinid, the bottlenose dolphin and a well-studied terrestrial mammal, the domestic dog are heavily drawn on.

Operando monitoring of gas bubble evolution in water electrolysis by single high-frequency impedance

A single frequency impedance method is introduced, based on an optimum high frequency of minimum phase and faradaic processes, to monitor gas bubble evolution during water electrolysis in operando.

(Invited) Elucidating the Hydrodynamic Behavior of Multi-Species Gas Bubbles in an Electrochemical Solvent Regenerator for Direct Air Capture

Direct Air Capture (DAC) is very significant to bolstering the global drive towards net negative emissions. DAC technologies/plants have emerged in recent years, with the regeneration of the capture solvent used in the process being the major bottleneck of most aqueous technologies. [1] Leveraging electrochemical principles has offered a potential opportunity to simplify the entire solvent regeneration process and potentially reduce its overall capture cost, compared to traditional approaches. The electrochemical approach also offers the benefit of direct integrating clean energy, and also eliminating the high thermal energy requirements of typical methods.[2] Despite these potentials, the complex three-phase (solid-liquid-gas) interaction on the electrode surface pose a significant impediment to this electrochemical approach for DAC. The evolution of gas bubbles in electrochemical cells are well-known to contribute to energy losses in such reactors, from previous studies. [3],[4],[5] Gas bubbles have been shown to influence ohmic overpotentials in electrochemical reactors and studies have shown that the energy demand for water electrolysis can be reduced by 10-25 percent if the formation of gas bubbles is suppressed. [6],[7] However, the evolution of gas bubbles in electrochemical systems remains a complicated issue requiring further investigation. This study advances previous work by investigating the simultaneous evolution of CO2 gas bubbles along with O2/H2 gas bubbles in an electrochemical reactor for DAC. Gas bubbles are infamous for their ability to cover the active area of electrodes, limiting the transport of reactive species to the electrode surface, thus, increasing cell resistance. In this work, we explore changes in the polarization and hydrodynamics behavior of gas bubbles in the electrolyzer used for DAC solvent regeneration owing to the evolution of CO2 bubbles from pH swing, and the implications of the additional CO2 bubble formation to electrode surface coverage. By using a high-speed camera, we observe that bubbles coverage appears to be larger at the edges of the electrodes, and that the orientation of the electrodes influence bubble coalescence and detachment rate. We also employ different cell designs to mitigate the impact of bubble surface coverage towards reducing cell resistance. References Sabatino, A. Grimm, F. Gallucci, M. Van Sint Annaland, G. J. Kramer, M. Gazzani, Joule, 5(8), 2047-2076 (2021).Gao, A. Omosebi, R. Perrone, K. Liu, Journal of The Electrochemical Society (2022).H. Li, Y. J. Chen, Scientific Reports, 11(1), 1-12 (2021).F. Swiegers, R. N. L.Terrett, G. Tsekouras, T. Tsuzuki, R. J. Pace, R. Stranger, Sustainable Energy & Fuels, 5(11), 3004–3004 (2021).Zhao, H. Ren, L. Luo, Langmuir, 35(16), 5392-5408 (2019).Mazloomi, N. B. Sulaiman, H. Moayedi, International Journal of Electrochemical Science, 7(4), 3314-3326 (2012).C. Wang, C. Y. Chen, Electrochimica Acta, 54(15), 3877-3883 (2009).

Electrocoagulation and electrooxidation technologies for pesticide removal from water or wastewater: A review.

Pesticides are known to be threats to the environment and human health. Excessive use of pesticides in agricultural practice can contaminate water bodies, leading to cancer, asthma, neurological disorders, reproductive defects, and hormonal disruption. Electrochemical methods such as electrocoagulation and electrooxidation can be used for pesticide removal due to their numerous advantages such as high efficiency, less sludge production, and low operational cost. During electrocoagulation, dissolution of anode metals results in metal hydroxide complexes, which precipitate with the contaminant present in the reactor. Simultaneously, electro-flotation occurs at the cathode and results in the evolution of hydrogen gas bubbles, leading to flotation of floc to the top surface of the reactor. This review focuses on the removal mechanisms, kinetics, modeling, effects of influencing factors, and sludge characterization of pesticide removal using electrocoagulation and electrooxidation. Major influencing factors include cell configuration, electrode material, current density, pH, supporting electrolyte concentration. In general, aluminum and iron are the most common electrodes used for pesticide removal using electrocoagulation, while boron-doped diamond was used to a far greater extent as the electrode in electrooxidation studies. Greater than 99% removal efficiency was observed in both processes. Overall, this review summarizes the use of electrochemical methods for pesticide removal and offers valuable information to researchers in this area of study.

Hydrodynamic characteristics and wake evolution of a submarine pipe with the presence of gas leakage at a low Reynolds number of 160

Hydrodynamic characteristics and wake structures of a submarine gas transmission pipe with the presence of gas leakage are of significance from a scientific and practical viewpoint. In this paper, we present a numerical investigation of flow past a leaking pipe at a low Reynolds number of 160 using the Eulerian–Eulerian multi-fluid volume of fluid model. The focus is on the effects of gas buoyancy and the location of the leak hole on the wake flow structures, bubble–vortex interference, and hydrodynamic forces. The variation of drag and lift coefficients is highly associated with the evolution of gas bubbles and the interaction between the bubble-induced vortices and the shear layers. When the gas buoyancy is ignored, the alterations of the main vortex structure and hydrodynamic forces are not sensitive to the location of the leak hole. The bubble-induced vortices are encompassed by the two shear layers and quickly dissolved in the main vortices. Finally, the released gas bubbles are locked in the center of main vortices and convected downstream with them. In contrast, when the buoyancy is considered, the gas bubbles line up in the upper shear layer, strongly interfering with the formation of the upper main vortex. Each gas bubble introduces a pair of small vortices that experience complicated merging or splitting during the migration. Consequently, the upper main vortex is suppressed at θ = 90° and vanished at θ = 180° and θ = 270° (θ is measured clockwise from the forward stagnation point), leading to the negative time-averaged lift force and the same-frequency oscillation of drag and lift coefficients. Due to the upward migration of gas bubbles from both front and rear surfaces at θ = 270°, the evolution of bubble-induced vortices is more complicated and the oscillation of hydrodynamic forces is significantly enhanced in comparison with other cases.