Lagrangian tracking of the cavitation bubble

Physical review letters, 2015

Cavitation bubbles induce impulsive forces on surrounding substrates, particles, or surfaces. Even though cavitation is a traditional topic in fluid mechanics, current understanding and studies do not capture the effect of cavitation on suspended objects in fluids. In the present work, the dynamics of a spherical particle due to a cavitation bubble is experimentally characterized and compared with an analytical model. Three phases are observed: the growth of the bubble where the particle is pushed away, its collapse where the particle approaches the bubble, and a longer time scale postcollapse where the particle continues to move toward the collapsed bubble. The particle motion in the longer time scale presumably results from the asymmetric cavitation evolution at an earlier time. Our theory considering the asymmetric bubble dynamics shows that the particle velocity strongly depends on the distance from the bubble as an inverse-fourth-power law, which is in good agreement with our e...

Journal of Fluid Mechanics, 1991

Aiche Journal, 1997

Harnessing the energy associated with cavitation for a number of physical and chemical changes has been pursued enthusiastically by sonochemists using ultrasound equipment of various sizes, shapes and forms. The effect of cavitation as observed in ultrasonic equipment has been attributed to the transient form of cavitation. Hydrodynamically generated cavities are believed to behave in a stable cavitation mode and, hence, are not very useful for the desired sonochemical effects.

2003

In the present paper, we focus on a specific type of bubble cavitation over a lifting hydrofoil generated in a periodic way, which turns into attached spot cavitation for high generation frequency. The aim of our work is a better understanding of the inception mechanism of such cavitation as well as its interaction with the liquid flow. Tests are conducted in EPFL cavitation tunnel on a 2-D Naca0009 hydrofoil equipped with miniature pressure sensors. Flow visualisation and pressure transient are recorded in synchronous way for several test conditions. For a given hydrodynamic conditions, the frequency of bubble generation is found to be different for two neighboring bubble sources. Generation frequencies, as high as 5 kHz were measured. We have shown that periodic bubble cavitation originates from a local vaporization process, which takes place within the surface roughness in the minimum pressure area. The pressure transient caused by a traveling bubble passage over the hydrofoil was analyzed. It turns out that the pressure beneath the bubble is always negative and well below the expected vapor pressure. Therefore, a thin film of liquid, which could correspond to the boundary layer, stands between the bubble and the solid surface. Moreover, we have shown that a moving 3-D boundary layer separation is produced behind the bubble.

Computers & Fluids, 2012

In this paper, we investigate the high-speed dynamics of symmetric and asymmetric cavitation bubble-collapse. For this purpose, a sharp-interface numerical model is employed, that includes a numerically effi-cient evaporation/condensation model. The underlying assumption is that phase change occurs in thermal non-equilibrium and that the associated timescale is much larger than that of the wave-dynamics described by the interfacial Riemann problem. The sharp-interface model allows for an accurate tracking of the interface evolution throughout collapse and rebound. With a first set of simulations, we investigate the influence of the non-equilibrium on the relaxation behaviour of an oscillating vapour bubble. We observe that a good prediction of the phase-change rate is essential. Of high practical interest is the col-lapse of cavitation bubbles near walls under high ambient-pressure conditions. We investigate the differ-ences in collapse evolution for detached and attached bubbles. It is shown that the maximum wall pressure strongly depends on the symmetry of the collapse mechanisms, and regions with a high proba-bility of bubble rebound are identified. Asymmetric attached bubbles lead to significantly different topol-ogy changes during collapse than symmetric bubbles but exhibit roughly the same range of maximum pressures.

2003

In the present paper, we focus on a specific type of bubble cavitation over a lifting hydrofoil generated in a periodic way, which turns into attached spot cavitation for high generation frequency. The aim of our work is a better understanding of the inception mechanism of such cavitation as well as its interaction with the liquid flow. Tests are conducted in EPFL cavitation tunnel on a 2-D Naca0009 hydrofoil equipped with miniature pressure sensors. Flow visualisation and pressure transient are recorded in synchronous way for several test conditions. For a given hydrodynamic conditions, the frequency of bubble generation is found to be different for two neighboring bubble sources. Generation frequencies, as high as 5 kHz were measured. We have shown that periodic bubble cavitation originates from a local vaporization process, which takes place within the surface roughness in the minimum pressure area. The pressure transient caused by a traveling bubble passage over the hydrofoil wa...

Physics of Fluids

This paper presents a numerical study of the dynamics of an initially spherical bubble collapse near an oscillating rigid wall with a large amplitude; the wall oscillating amplitude is greater than 1% of the initial maximum bubble radius. Numerical simulations were conducted using a compressible two-phase flow model and the volume of fluid (VOF) interphase-sharpening technique on a general curvilinear moving grid. The numerical results for bubbles in the free field and near a wall were computed and compared with published experimental data. To study the effects of the oscillating wall on bubble collapse, a sinusoidal function was used for wall oscillation. The initial bubble conditions were set as a Rayleigh bubble located above the rigid wall at a dimensionless bubble-boundary distance with initial phases of 0{degree sign} and 180{degree sign}. During bubble collapse, the interface deformation, jetting behavior, bubble collapse time, and bubble migration were determined. Violent co...

Advances in Modeling of Fluid Dynamics, 2012

Journal of Fluid Mechanics, 1995

Recent observations of growing and collapsing bubbles in flows over axisymmetric headforms have revealed the complexity of the 'micro-fluid-mechanics ' associated with these bubbles Brianqon-Marjollet et al. 1990;. Among the complex features observed were the bubble-tobubble and bubble-to-boundary-layer interactions which leads to the shearing of the underside of the bubble and alters the collapsing process. All of these previous tests, though, were performed on small headform sizes. The focus of this research is to analyse the scaling effects of these phenomena due to variations in model size, Reynolds number and cavitation number. For this purpose, cavitating flows over Schiebe headforms of different sizes (5.08, 25.4 and 50.8 cm in diameter) were studied in the David Taylor Large Cavitation Channel (LCC). The bubble dynamics captured using high-speed film and electrode sensors are presented along with the noise signals generated during the collapse of the cavities.

International Journal of Multiphase Flow, 2018

In this paper, the performance of three different numerical approaches in cavitation modelling are compared by studying two benchmark test cases to understand the capabilities and limitations of each method. Two of the methods are the well established compressible thermodynamic equilibrium mixture model and the incompressible transport equation finite mass transfer mixture model, which are compared with a third method, a recently developed Lagrangian discrete bubble model. In the Lagrangian model, the continuum flow field is treated similar to the finite mass transfer approach, however the cavities are represented by individual bubbles. Further, for the Lagrangian model, different ways to consider how the fluid pressure influences bubble dynamics are studied, including a novel way by considering the local pressure effect in the Rayleigh-Plesset equation. The first case studied is the Rayleigh collapse of a single bubble, which helps to understand each model behaviour in capturing the cavity interface and the surrounding pressure variations. The special differences between the Lagrangian and finite mass transfer models in this case clarify some possible origin for some limitations of the latter method. The second investigated case is the collapse of a cluster of bubbles, where the collapse of each bubble is affected by the dynamics of surrounding bubbles. This case confirms the importance of considering local pressure in the improved form of the Rayleigh-Plesset equation and illustrates the influence of the liquid compressibility for cavity modelling and appropriate capturing of the collapse pressure.