Surface tension effects on the behavior of two cavities near a rigid wall.
TL;DR: For a convex cavity, surface tension has the effects on cavity behavior similar to those of the difference between the ambient pressure and the saturated vapor pressure inside the cavities.
Abstract: Surface tension effects on the behavior of two initially spherical cavities growing and collapsing axisymmetrically above and near a rigid wall are investigated numerically by boundary integral method. The numerical simulations are performed for different dimensionless maximal cavity sizes, different dimensionless distances between the two cavities and those between the wall and the two cavities, and different values of Weber number. It is found that surface tension effects will resist the deformation of a cavity and make it closer to spherical during its growth phase, and make it collapse faster. For the case where the lower cavity is much smaller than the upper one, when the Weber number is less than or equal to 20, during the collapse phase, surface tension will have substantial effects on the behavior of the lower cavity such as change the form or the direction of its liquid jet if the Bjerknes forces to the lower cavity induced by the wall and the upper one are nearly equal. In all of the other cases, when the Weber number is greater than or equal to 10, surface tension will not have qualitative effects on the behavior of the cavity but change the length, width or sizes of its liquid jet. It is also found that for a convex cavity, surface tension has the effects on cavity behavior similar to those of the difference between the ambient pressure and the saturated vapor pressure inside the cavities. The above phenomena induced by surface tension effects are explained by this mechanism.
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TL;DR: In this article, the interaction between two oscillating differently sized bubbles (generated in tap water) is studied using high speed photography, and the behavior of the bubbles is fully characterized by their dimensionless separation distance, their phase difference, and their size ratio.
Abstract: Most real life bubble dynamics applications involve multiple bubbles, for example, in cavitation erosion prevention, ultrasonic baths, underwater warfare, and medical applications involving microbubble contrast agents. Most scientific dealings with bubble-bubble interaction focus on two similarly sized bubbles. In this study, the interaction between two oscillating differently sized bubbles (generated in tap water) is studied using high speed photography. Four types of bubble behavior were observed, namely, jetting toward each other, jetting away from each other, bubble coalescence, and a behavior termed the "catapult" effect. In-phase bubbles jet toward each other, while out-of-phase bubbles jet away from each other. There exists a critical phase difference that separates the two regimes. The behavior of the bubbles is fully characterized by their dimensionless separation distance, their phase difference, and their size ratio. It is also found that for bubbles with large size difference, the smaller bubble behaves similarly to a single bubble oscillating near a free surface.
57 citations
01 Dec 2011
TL;DR: In this study, the interaction between two oscillating differently sized bubbles (generated in tap water) is studied using high speed photography, and it is found that for bubbles with large size difference, the smaller bubble behaves similarly to a single bubble oscillating near a free surface.
Abstract: Most real life bubble dynamics applications involve multiple bubbles, for example, in cavitation erosion prevention, ultrasonic baths, underwater warfare, and medical applications involving microbubble contrast agents. Most scientific dealings with bubble-bubble interaction focus on two similarly sized bubbles. In this study, the interaction between two oscillating differently sized bubbles (generated in tap water) is studied using high speed photography. Four types of bubble behavior were observed, namely, jetting toward each other, jetting away from each other, bubble coalescence, and a behavior termed the "catapult" effect. In-phase bubbles jet toward each other, while out-of-phase bubbles jet away from each other. There exists a critical phase difference that separates the two regimes. The behavior of the bubbles is fully characterized by their dimensionless separation distance, their phase difference, and their size ratio. It is also found that for bubbles with large size difference, the smaller bubble behaves similarly to a single bubble oscillating near a free surface.
52 citations
TL;DR: In this paper, a spark-generated bubble (through a short circuit with two electrodes) was generated near a stationary smaller bubble in order to keep the millimeter-sized bubble stationary, it was trapped in a droplet of silicone oil attached to one of the electrodes.
Abstract: An oscillating bubble near another (stationary) bubble can give rise to interesting interactions Such a nonequilibrium (oscillating) bubble can create a jet in a smaller nearby (initially stationary) bubble as demonstrated in this study both experimentally and numerically In the experimental study, a spark-generated bubble (through a short circuit with two electrodes) was generated near a stationary smaller bubble In order to keep the millimeter-sized bubble stationary, it was trapped in a droplet of silicone oil attached to one of the electrodes The jet in the initially stationary bubble can reach velocities up to 250 m/s, but the velocity becomes lower for bubbles that are larger or situated further away The current article also describes some experiments with the appearance of a crown-like secondary jet on the free surface (regarded as a large stationary bubble) relatively long after the bubble has collapsed Some other interesting interactions of a spark-generated bubble with more than one stationary bubble are presented
36 citations
TL;DR: In this paper, two oscillating vapor bubbles with similar size are generated simultaneously near a rigid wall in axisymmetric configuration using the underwater electric discharge method, and the physical process is captured by a high-speed camera.
Abstract: Two-bubble interaction is the most fundamental problem in multi-bubbles dynamics, which is crucial in many practical applications involving air-gun arrays and underwater explosions. In this paper, we experimentally and numerically investigate coalescence, collapse, and rebound of non-buoyant bubble pairs below a rigid wall. Two oscillating vapor bubbles with similar size are generated simultaneously near a rigid wall in axisymmetric configuration using the underwater electric discharge method, and the physical process is captured by a high-speed camera. Numerical simulations are conducted based on potential flow theory coupled with the boundary integral method. Our numerical results show excellent agreement with the experimental data until the splashing of the jet impact sets in. With different ranges of γbw (the dimensionless distance between the rigid wall and the nearest bubble center), the interaction between the coalesced bubble and the rigid wall is divided into three types, i.e., “weak,” “intermedi...
26 citations
TL;DR: The jet and shock wave phenomenon in the interaction of two cavitation bubbles are tested and the two bubbles are more likely to form a face-to-face collapse, and the smaller the distance between the two, the easier it is to fuse.
Abstract: As a common hydrodynamic phenomenon, multi-cavitation dynamics is widely found in many industries such as hydraulic engineering, shipping industry and chemical industry. The jet and shock wave phenomenon in the interaction of two cavitation bubbles are the basis of multi-cavitation bubbles interaction research. By respectively inducing two cavitation bubbles through laser and underwater low-voltage discharge, this paper tested the jet and shock wave resulting from the collapse of the two cavitation bubbles, and the following conclusions are obtained: (1) If the two cavitation bubbles are synchronously generated but in different size, as the distance between the two cavitation bubbles increases or the maximum radius of the smaller cavitation bubble increases, the effect of the small cavitation bubble on the larger one gradually changes from the surface wave phenomenon to jet that breaks through the larger bubble. When the two bubble center lines are parallel to the wall surface, this jet suppresses the formation of the jet to the wall surface when the large cavitation bubble collapses; if the two cavitation bubbles are generated at the same time with same size, as the initial distance of the two cavitation bubbles gradually decreases, the two bubbles are more likely to form a face-to-face collapse, and the smaller the distance between the two, the easier it is to fuse. (2) The impact of the initial moment of the cavitation bubble on the structure of the collapse shock wave is as follows: for two bubbles of different sizes formed synchronously, the shock wave propagates to the periphery in the form of a number of consecutive waves appearing in the larger bubble, while for the unsynchronized ones, shock waves appeared in both cavitation collapses, and a number of consecutive waves appear in the late-formed cavitation bubble. And multiple consecutive shock waves may overlap in some areas of the space. These conclusions have obvious implications for preventing cavitation damage and utilization of cavitation.
22 citations