Numerical simulation of a collapsing bubble subject to gravity

Abstract

Abstract. The present paper focuses on the simulation of the expansion and aspherical collapse of a laser-generated bubble subjected to an acceleration field and comparison of the results with instances from high-speed videos. The interaction of the liquid and gas is handled with the Volume Of Fluid (VOF) method. Compressibility effects have been included for each phase to predict the propagation of pressure waves. Initial conditions were estimated through the Rayleigh Plesset equation, based on the maximum bubble size and collapse time. The simulation predictions indicate that during the expansion the bubble shape is very close to spherical. On the other hand, during the collapse the bubble point closest to the bottom of the container develops a slightly higher collapse velocity than the rest of the bubble surface. Over time, this causes momentum focusing and leads to a positive feedback mechanism that amplifies the collapse locally. At the latest collapse stages, a jet is formed at the axis of symmetry, with opposite direction to the acceleration vector, reaching velocities of even 300m/s. The simulation results agree with the observed bubble evolution and pattern from the experiments, obtained using high speed imaging, showing the collapse mechanism in great detail and clarity.

Laser‐Induced Forward Transfer: Fundamentals and Applications

“…The mechanism responsible for the jetting dynamics is essentially the same as that of the evolution of a bubble generated close to the free surface of a liquid, a typical problem in fluid mechanics which has been analyzed both experimentally and through numerical calculation . In the case of LIFT there are a few differences, though, all of them arising from the presence of the rigid donor substrate adjacent to one side of the laser‐generated bubble.…”

Numerical investigation of the role of heat transfer in bubble dynamics

“…In the ideal gas ones, the heat transfer between the bubble and the liquid is not predefined (adiabatic or isothermal), but becomes part of the solution. In Figure 2a, the case of bubble collapse ( ) is considered and the conditions examined are identical to those examined in [16] ( 10 5 Pa, 6900 Pa); for the ideal gas case, both the liquid and the gas have an initial temperature of 300 K. In Figure 2b, the case of bubble growth is considered ( 10 5 Pa, 30 10 5 Pa); with an initial bubble temperature of 2500 K, higher than the initial liquid temperature. A first glimpse shows that the effect of heat transfer is quite important for the bubble expansion case compared to the bubble collapse one, while the ideal gas curve is not between the limiting conditions of isothermal and adiabatic behaviour as expected.…”

“…For the latter cases, the bubble density obeys a polytropic gas equation of state ( ), where the constant parameter κ is set according to a reference state for gas pressure and density. The thermal VOF model has been extensively used in a number of studies from the authors' group in deforming droplet simulations such as in [10][11][12] and in [13][14][15], but also in cases with polytropic bubble dynamics as in [16,17]. The model equations have been presented in detail in the aforementioned works and thus they are not repeated here.…”

“…During the whole phenomenon, heat and work are in phase between them, while the ratio of their maximum absolute was computed equal to ̇ ̇ 0.2; the latter manifests the significance of heat transfer to the evolution of the phenomenon. The analysis that follows in the rest of the paper concerns only cases of bubble collapse, while the reference operating conditions in [16] are used, as in Figure 2a. In order to relate the temporal evolution of ̇ provided by the CFD simulations (considered to be the actual one) with that of ̇ (Eq.…”

Rebounds of deformed cavitation bubbles

“…1 arXiv:1810.12287v1 [physics.flu-dyn] 29 Oct 2018 derstanding the underlying physics has motivated numerous studies to look at simplified case studies, especially involving the first collapse of single cavitation bubbles in various conditions. A great deal is indeed known about these bubbles and how they are able to emit microjets moving at hundreds of meters per second [11,12], shock waves with peak pressures reaching thousands of atmospheres [13][14][15], and luminescence, i.e., light emission due to the extreme heating of the bubble interior reaching thousands of degrees in temperature [16,17].Our understanding of these processes comes from the combination of experimental studies, often using laser- [13,[18][19][20], spark-[21-23], or ultrasound-induced [24, 25] cavitation bubbles; numerical studies typically using boundary integral methods [18,[26][27][28][29][30] and domain methods [31][32][33][34][35]; and analytical studies, most of them considering bubbles collapsing spherically [36][37][38][39][40][41][42] but some also tackling non-spherical bubble shapes, for example, by using the concept of Kelvin impulse [43,44].Non-sphericity adds a lot of complexity to the modeling of the bubble collapse. We also do not precisely know the composition, the quantity, the source, or the behavior of the gaseous contents of a typical cavitation bubble in its most extreme collapse conditions, making accurate modeling even more challenging.…”