Particle motion induced by bubble cavitation

Physics of Fluids

Hard particle erosion and cavitation damage are two main wear problems that can affect the internal components of hydraulic machinery such as hydraulic turbines or pumps. If both problems synergistically act together, the damage can be more severe and result in high maintenance costs. In this work, a study of the interaction of hard particles and cavitation bubbles is developed to understand their interactive behavior. Experimental tests and numerical simulations using computational fluid dynamics (CFD) were performed. Experimentally, a cavitation bubble was generated with an electric spark near a solid surface, and its interaction with hard particles of different sizes and materials was observed using a high-speed camera. A simplified analytical approach was developed to model the behavior of the particles near the bubble interface during its collapse. Computationally, we simulated an air bubble that grew and collapsed near a solid wall while interacting with one particle near the bubble interface. Several simulations with different conditions were made and validated with the experimental data. The experimental data obtained from particles above the bubble were consistent with the numerical results and analytical study. The particle size, density and position of the particle with respect to the bubble interface strongly affected the maximum velocity of the particles.

Journal of Fluid Mechanics, 1993

During the collapse of an initially spherical cavitation bubble near a rigid wall, a reentrant jet forms from the side of the bubble farthest from the wall. This re-entrant jet impacts and penetrates the bubble surface closest to the wall during the final stage of the collapse. In the present paper, this phenomenon is modelled with potential flow theory, and a numerical approach based on conventional and hypersingular boundary integral equations is presented. The method allows for the continuous simulation of the bubble motion from growth to collapse and the impact and penetration of the reentrant jet. The numerical investigations show that during penetration the bubble surface is transformed to a ring bubble that is smoothly attached to a vortex sheet. The velocity of the tip of the re-entrant jet is always directed toward the wall during penetration with a speed less than its speed before impact. A high-pressure region is created around the penetration interface. Theoretical analysis and numerical results show that the liquid-liquid impact causes a loss in the kinetic energy of the flow field. Variations in the initial distance from the bubble centre to the wall are found to cause large changes in the details of the flow field. No existing experimental data are available to make a direct comparison with the numerical predictions. However, the results obtained in this study agree qualitatively with experimental observations.

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 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.

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.

Soft Matter, 2014

Many applications such as ultrasonic cleaning or sonochemistry use the ability of bubbles to oscillate and drive liquid flow. But bubbles have also received attention in porous media, where drying may cause cavitation, a phenomenon occurring in plant tissues. Here we explore the dynamics of cavitation bubbles when the liquid is fully entrapped in an elastic solid, using light scattering, laser strobe photography and high speed camera recordings. Our experiments show unexpectedly fast bubble oscillations in volume. They depend on the confinement size and elasticity, which we explain with a simple model where liquid compressibility is a key parameter. We also observe rich non-spherical dynamics, with ejection away from the walls and bubble fragmentation, which reveal extreme fluid motion at short timescales.

International Journal of Mineral Processing, 2013

and sharing with colleagues.

EPJ Web of Conferences

Cavitation bubbles generated via laser-induced breakdown are investigated experimentally. The present work focuses on the direction of the first bubble collapse near a solid surface in distilled water. The solid surface is placed first to the right side in a cuvette filled with distilled water and then placed to the top of the cuvette. In this experiment, it is observed in which direction the cavitation bubble collapses. The cavitation bubble is visualized by a high-speed camera of frequency 68kHz.

Journal of Fluid Mechanics, 1991

A new insight to the role of bubble properties on inertial effect in particle–bubble interaction

JSME International Journal Series B, 2002

The present paper reports observation results of collapsing cavity bubbles on a two-dimensional foil section by a highspeed video camera, together with impulsive force measurement. Results of numerical simulations of the behavior of bubble cluster corresponding to the above condition are also shown. With these materials the authors discuss the mechanism of generation of the impulsive force due to cavitation collapse.

1997

Abstract: The understanding of the fundamental mechanisms involved in the interaction between bubbles/free surfaces and vortical flows is of relevance to many important naval applications. Classical assumptions of bubble sphericity and decoupling between bubble and flow behavior prevent one from capturing essential elements of the interaction, and might lead to incorrect conclusions with serious consequences. Bubble motion and deformation are seen to be of great importance for most bubbles in the size spectrum.

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...

International Journal of Mineral Processing, 2003

Bubble -particle interaction during flotation comprises of collision, attachment and detachment. This paper presents a review of our investigations into these microprocesses. Analysis of collision phenomenon focuses on the physicochemical hydrodynamics of water flow passing the rising bubbles. The influence of the fore-and-aft asymmetry of water streamlines and of the mobility of the bubble surface on collision efficiency is quantified. In the case of attachment, the analysis considers contact and attachment times and reveals that the available models for contact times are far from satisfactory. It may be necessary to include short-range hydrodynamic interactions for the modeling of contact times. At present, the actual attachment time is difficult to predict from first principles. Finally, the examination of detachment focuses on models for predicting the tenacity of attached particles. The influence of the bubble size on tenacity is also analyzed. Simplified equations describing the maximum particle size for stable attachment to air bubbles are derived. D

Journal of Colloid and Interface Science, 1998

form a permanent aggregate, a process which, in modern The collection efficiency of single bubbles rising through a very flotation science, is referred to as orthokinetic heterocoaguladilute pulp of hydrophobized quartz particles has been detertion (14, 15). The collection efficiency is the product of the mined. Measurements have been performed under conditions in efficiencies of three steps (or processes) involved in partiwhich the bubble surface is mobile, as a function of electrolyte cle-bubble interaction (16); i.e., concentration, particle diameter (7 to 70 mm) , bubble diameter (0.77 1 10 03 to 1.52 1 10 03 m), and particle advancing water contact angle. Situations in which the product of attachment and