摘要 :
The underwater explosion bubbles have significant applications in the military, but the characteristics of bubble jet near a solid wall are still not very clear. Due to convenience and high efficiency, the boundary integral method...
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The underwater explosion bubbles have significant applications in the military, but the characteristics of bubble jet near a solid wall are still not very clear. Due to convenience and high efficiency, the boundary integral method is used to study the characteristics of bubble jet in this paper. The shape of bubble jet is simplified to a cylindrical shape when the jet impacts on the opposite surface, so the characteristics of bubble jet are characterized by three parameters, including the cylindrical width (diameter), the cylindrical height and the jet velocity. By adjusting the charge weight W, the detonated depth H and the stand-off distance parameter gamma (gamma = (H - h)/R-m, where h is the depth of solid wall, and R-m is the maximum bubble radius), the relations of the bubble jet width, height and velocity with them are explored, where three appropriate mathematical models are selected. Finally, based on the least square method, three estimate formulas for bubble jet width, height and velocity are obtained, which have good accuracy to predict the bubble jet width, height and velocity when W = 50-1000 kg, h = 50-500 m and gamma = 0.65-1.5. The purpose is to provide a reference for computing the damage of the bubble jet to structures in engineering.
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Optical imaging experiments were conducted to investigate regimes of bubbling when two vertical gas jets are injected into liquids. Three regimes were identified (i) bubbles break off from jets independently of one another, (ii) b...
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Optical imaging experiments were conducted to investigate regimes of bubbling when two vertical gas jets are injected into liquids. Three regimes were identified (i) bubbles break off from jets independently of one another, (ii) bubbles coalesce and break off from jets at the same time and (iii) bubbles break off from jets in an alternating pattern, nearly 180 degrees out-of-phase from one another. We identify that a mixed capillary number is key to determining the size of bubbles. Further, we find that the ratio of bubble diameter at breakoff to separation distance between jets is key to determining the regime of bubble breakoff. The alternating pattern is attributed to a growing jet pushing liquid between the two jets towards the second jet, such that the second jet pinches off, forming a bubble. This mechanism is used to formulate a simplified coupled harmonic oscillator model which captures alternating bubbling. (c) 2021 Elsevier Ltd. All rights reserved.
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A tube filled with a perfectly wetting liquid falls axially under its own weight. In its gravity-free reference frame, the liquid interface is deformed by surface tension into a hemispherical shape. On impact of the tube on a rigi...
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A tube filled with a perfectly wetting liquid falls axially under its own weight. In its gravity-free reference frame, the liquid interface is deformed by surface tension into a hemispherical shape. On impact of the tube on a rigid floor, the interface curvature reverses violently, forming a concentrated jet. If the contact angle at the tube wall is such that the interface is flat, the liquid rebounds as a whole with the tube, with no deformation. We analyse this phenomenon using an impulse pressure description, providing an exact description of the initial liquid velocity field at the impact, supported by high-speed image velocimetry measurements. This initial dynamics is insensitive to liquid surface tension and viscosity.
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A study was performed to characterize the different bubble formation regimes that occur during the process of gas jet injection into a liquid cross flow in a conduit. Air was injected perpendicularly into a turbulent, fully develo...
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A study was performed to characterize the different bubble formation regimes that occur during the process of gas jet injection into a liquid cross flow in a conduit. Air was injected perpendicularly into a turbulent, fully developed water flow circulating through a 12.7 mm square channel. Three different gas injectors, with diameters of 0.27 mm, 0.52 mm, and 1.59 mm were used. The bulk water velocity values ranged between 1.1 and 4.3 m/s. The effects that the gas injection velocity, liquid mean velocity, and injection gas injection diameter have on the process of bubble generation were investigated. A high-speed visualization technique was used to determine the regimes near the gas inlet region. Four distinct regimes were identified: Single Bubbling (SB), Pulse (P), Elongated Jetting (EJ), and Atomizing Jetting (AJ). It was observed that the shift between regimes occurs gradually, producing the need to identify transitional regions: SBP and PTJ. Sets of independent dimensionless variables were used to categorize the proposed regimes using bubble formation maps. It was determined that the injection diameter plays a primary role in jet formation: as the injection diameter increased, the observable number of regimes decreased, indicating a more stable and continuous process of bubble generation. Empirical correlations that delimit the boundaries between ordered and chaotic bubble generation are presented.
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Gas dispersion from an orifice located in the non-separated flow region of a cylindrical impeller blade was investigated, with four regimes ranging from discrete, orderly bubbling to stable jetting being identified. A prediction o...
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Gas dispersion from an orifice located in the non-separated flow region of a cylindrical impeller blade was investigated, with four regimes ranging from discrete, orderly bubbling to stable jetting being identified. A prediction of the upper limit for the discrete bubbling regime corresponded well with that of previous authors. An algorithm which balances the pressure loss as gas flows through the system with the driving pressure gradient derived from potential flow theory was developed to model the gas flow rate for a given liquid flow past the orifice. Model predictions are compared with experimental measurements. [References: 14]
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A vapor bubble collapsing near a solid boundary in a liquid produces a liquid jet that points toward the boundary. The direction of this jet has been studied for boundaries such as flat planes and parallel walls enclosing a channe...
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A vapor bubble collapsing near a solid boundary in a liquid produces a liquid jet that points toward the boundary. The direction of this jet has been studied for boundaries such as flat planes and parallel walls enclosing a channel. Extending these investigations to enclosed polygonal boundaries, we experimentally measure jet direction for collapsing bubbles inside a square and an equilateral triangular channel. Following the method of Tagawa and Peters [Phys. Rev. Fluids 3, 081601 (2018)] for predicting the jet direction in corners, we model the bubble as a sink in a potential flow and demonstrate by experiment that analytical solutions accurately predict jet direction within an equilateral triangle and square. We further use the method to develop predictions for several other polygons, specifically, a rectangle, an isosceles right triangle, and a 30?-60?-90? right triangle.
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This paper presents an experimental study on the pulsation characteristics of bubbles under a damaged boundary. Bubble phenomena in the fluid domain, such as bubble shape, pulsation period, water jet, and motion, are observed, and...
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This paper presents an experimental study on the pulsation characteristics of bubbles under a damaged boundary. Bubble phenomena in the fluid domain, such as bubble shape, pulsation period, water jet, and motion, are observed, and the influence of distance parameters on these phenomena is analyzed in detail with the help of high-speed photography technology. We also discuss the relationship between bubble pulsation, the water spike form, and characteristic parameters under different boundary conditions, such as different hole shapes. It is found that the broken boundary weakens the effect of the wall on bubble motion, while the shape and area of the hole exert noticeable effects on the water spike. In addition, the rising part of the free surface consisting of three parts, the water spike, water skirt I, and water skirt II, along with their evolutionary forms at the gas-liquid interface, are experimentally studied.
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Oscillating bubbles or non-equilibrium bubbles are known to induce the development of liquid jets in the presence of a nearby rigid boundary. The liquid jets can be useful in many applications such as surface cleaning and drug del...
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Oscillating bubbles or non-equilibrium bubbles are known to induce the development of liquid jets in the presence of a nearby rigid boundary. The liquid jets can be useful in many applications such as surface cleaning and drug delivery into biological cells. Single bubble oscillation near a rigid boundary has been studied in detail in the literature. In this paper, we extend the research in this area to a two-bubble system near a rigid boundary using high speed photography. Various measurements on the direction of the (bubble-collapse induced) water jets were performed. We identified the parameter sets where the influence of the adjacent bubble and the rigid boundary is important. The experimental results are summarized in a graph that enables easy prediction of the direction of the water jets induced by bubble collapse near another bubble and a rigid boundary.
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An experimental and computational investigation was conducted to study the interaction between bubbles generated by an underwater explosive (UNDEX) and a nearby steel plate structure. The experiments were performed for different s...
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An experimental and computational investigation was conducted to study the interaction between bubbles generated by an underwater explosive (UNDEX) and a nearby steel plate structure. The experiments were performed for different standoff distances to investigate the interaction between the gas bubble and the rigid structure. High-speed photography was utilized to capture the underwater explosive gas bubble's behavior, and a series of pressure transducers were used to record the emitted pressure histories. The numerical simulations were performed with the Dynamic System Mechanics Advanced Simulation software, which is a full y coupled Eulerian-Lagrangian fluid-structure interaction code. The numerical simulations were validated with the experiments in terms of the detonation pressure, structural surface pressures, and UNDEX gas bubble growth and collapse. Results show that the UNDEX standoff distance greatly influences the gas bubble's shape, migration speed, bubble jetting behavior, and loading into its adjacent structure. Moreover, the impulse generated by the shock wave on the plate surface proved to be small in comparison to the impulse generated by the collapse of the UNDEX gas bubble. The magnitude of impulse depends on standoff distance, collapse symmetry, and relative collapse location. Published by Elsevier Ltd.
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We demonstrate dynamics of a bubble collapsing near a floating ice cake and its damage capabilities by virtue of high-speed jet and emitted shockwave, by doing indoor experiments in a water tank in a cold room. An ice cake is made...
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We demonstrate dynamics of a bubble collapsing near a floating ice cake and its damage capabilities by virtue of high-speed jet and emitted shockwave, by doing indoor experiments in a water tank in a cold room. An ice cake is made of fresh water in a cryostat, processed and placed in a water tank in a cold room, while the bubble is generated by electric spark at a distance beneath the floating ice cake. Their interaction is observed and recorded by a high-speed camera. A new observation technique is developed to observe the dynamics of bubble and ice simultaneously. The dynamics of the bubble involving bubble jet and shock wave are captured and the damage effects of bubble loads on the ice, including cracks, breakup and movement, are analyzed. It is found that three damage patterns can be generated on the ice according to the damage degree and crack development: crevasse pattern, radial and circumferential cracks pattern and radial cracks pattern. On this basis, the effects of ice thickness and the distance between the bubble and ice are studied and the possible referential ranges of the damage effects of bubble loads with these two parameters are investigated. It can be seen from the experiments that the collapse of the bubble can cause violent damage to the ice. (C) 2019 Elsevier Ltd. All rights reserved.
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