scholarly journals Synthetic jet generation by high-frequency cavitation

2017 ◽  
Vol 823 ◽  
Author(s):  
Milad Mohammadzadeh ◽  
Silvestre Roberto Gonzalez-Avila ◽  
Kun Liu ◽  
Qi Jie Wang ◽  
Claus-Dieter Ohl
Keyword(s):  
High Frequency ◽  
Laser Power ◽  
High Speed ◽  
Bubble Formation ◽  
Acoustic Streaming ◽  
High Repetition Rate ◽  
Synthetic Jet ◽  
Bubble Collapse ◽  
High Speed Photography ◽  
Bubble Interactions

Cavitation bubbles are nucleated at a high repetition rate in water by delivering a pulsed laser through a fibre optic. Continuous high-frequency cavitation drives a stream away from the fibre tip. Using high-speed photography and particle image velocimetry, the stream is characterised as a synthetic jet, generated by trains of vortices induced by non-spherical bubble collapse. At low laser power, the bubbles collapse before the arrival of a subsequent laser pulse. Yet, by increasing the laser power, a system of bubbles is formed which leads to complex bubble–bubble interactions. The synthetic jet is observed regardless of the bubble formation regime, demonstrating the stability of the phenomenon. Synthetic jet generation by repetitive bubble collapse extends the well-studied acoustic streaming from small-amplitude bubble oscillations.

scholarly journals A Photographic Study of Spark-Induced Cavitation Bubble Collapse

1972 ◽  
Vol 94 (4) ◽  
pp. 825-832 ◽  
Author(s):  
C. L. Kling ◽  
F. G. Hammitt
Keyword(s):  
Cavitation Bubble ◽  
High Speed ◽  
Bubble Collapse ◽  
Solid Boundary ◽  
High Speed Photography ◽  
Minimum Volume ◽  
Cavitation Bubbles ◽  
Flowing System

The collapse of spark-induced cavitation bubbles in a flowing system was studied by means of high speed photography. The migration of cavitation bubbles toward a nearby solid boundary during collapse and rebound was observed. Near its minimum volume the bubble typically formed a high speed microjet, which struck the nearby surface causing individual damage craters on soft aluminum.

Dynamics of laser-induced cavitation bubbles near two perpendicular rigid walls

2018 ◽  
Vol 841 ◽  
pp. 28-49 ◽  
Author(s):  
Emil-Alexandru Brujan ◽  
Tatsuya Noda ◽  
Atsushi Ishigami ◽  
Toshiyuki Ogasawara ◽  
Hiroyuki Takahira
Keyword(s):  
High Speed ◽  
Vertical Wall ◽  
Bubble Surface ◽  
Bubble Collapse ◽  
High Speed Photography ◽  
Maximum Expansion ◽  
Toroidal Bubble ◽  
Horizontal Wall ◽  
The Moment ◽  
Rigid Walls

The behaviour of a laser-induced cavitation bubble near two perpendicular rigid walls and its dependence on the distance between bubble and walls is investigated experimentally. It was shown by means of high-speed photography with $100\,000~\text{frames}~\text{s}^{-1}$ that an inclined jet is formed during bubble collapse and the bubble migrates in the direction of the jet. At a given position of the bubble with respect to the horizontal wall, the inclination of the jet increases with decreasing distance between the bubble and the second, vertical wall. A bubble generated at equal distances from the walls develops a jet that is directed in their bisection. The penetration of the jet into the opposite bubble surface leads to the formation of an asymmetric toroidal bubble that is perpendicular to the jet direction. At a large distance from the rigid walls, the toroidal bubble collapses in the radial direction, eventually disintegrating into tiny microbubbles. When the bubble is in contact with the horizontal wall at its maximum expansion, the toroidal ring collapses in both radial and toroidal directions, starting from the bubble part opposite to the vertical wall, and the bubble achieves a crescent shape at the moment of second collapse. The bubble oscillation is accompanied by a strong migration along the horizontal wall.

scholarly journals Experimental and Numerical Investigation of Bubble–Bubble Interactions during the Process of Free Ascension

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1977 ◽  
Author(s):  
Huang Ying ◽  
Gao Puzhen ◽  
Wang Chaoqun
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Momentum Equation ◽  
Velocity Variation ◽  
High Speed Photography ◽  
Movement Trajectory ◽  
Bubble Interactions ◽  
Cyclical Process ◽  
Velocity Changes ◽  
Two Bubbles

The shape and rising behavior of the horizontally arranged twin bubbles in a steady liquid are experimentally studied employing high-speed photography and digital image processing, and numerically studied by the Volume-Of-Fluid (VOF) method, in combination with a momentum equation coupled with a surface tension model. The movement trajectory and the velocity variation in horizontal and vertical directions of the horizontally arranged twin bubbles rising side by side, as observed in experiments, are described. According to the results, when two bubbles rise side by side, their horizontal velocity changes by the simple harmonic law; there is a cyclical process of two bubbles repeatedly attracted to and bounced against each other, rather than at constant distance between each other, and the bubbles swing up and down periodically in the water. The mathematical model and its numerical implementation are presented in detail. The validation of the model is confirmed by comparing the numerical and experimental results, which are in good agreement with each other; the numerical simulation can accurately reproduce the deformation, attraction, and repulsion of the bubble pairs. The phenomenon of attraction and repulsion is comprehensively analyzed from the viewpoint of a flow field. It is considered that the interaction between the bubbles is mainly influenced by the changes of the flow field due to vortex counteraction and wake merging effects.

Thermal-Fluid Phenomena Induced by Nanosecond-Pulse Heating of Materials in Water

2001 ◽  
Vol 123 (6) ◽  
pp. 1123-1132 ◽  
Author(s):  
I. Ueno ◽  
M. Shoji
Keyword(s):  
High Speed ◽  
Bubble Formation ◽  
Water System ◽  
Solid Material ◽  
Laser Wavelength ◽  
High Speed Photography ◽  
Time Resolved ◽  
Pump And Probe ◽  
Shock Wave Generation ◽  
Speed Up

Thermal-hydraulic phenomena adjacent to the liquid metal-water and solid material-water interfaces induced by nanosecond pulsed Nd:YAG laser (wavelength: 532 nm, FWHM: ∼13 ns) heating with the fluence F of 5.0×101∼1.0×103 mJ/cm2 were experimentally investigated. By applying the high-speed photography with a frame speed up to 2.0×107 fps, the aspects of the bubble formation, shock wave generation and propagation were observed. The bubble formation on the heated material’s surface of about 80 nm in diameter was detected in Si-water system from the time-resolved reflection (TRR) signal by applying the pump and probe method.

Vibration Mechanisms of a Heated Rod Due to Subcooled Boiling Flow

2006 ◽  
Author(s):  
M. R. Nematollahi ◽  
M. H. Akbari
Keyword(s):  
Quantitative Estimate ◽  
High Speed ◽  
Bubble Formation ◽  
Heating Surface ◽  
High Speed Photography ◽  
Subcooled Boiling ◽  
Bubble Behavior ◽  
Boiling Flow ◽  
Excitation Force ◽  
Power Densities

Vibration characteristics of subcooled boiling flow on thin and long structures such as a heating rod were recently investigated by the authors. The results show that the intensity of the subcooled boiling-induced vibration (SBIV) was influenced strongly by the conditions of subcooling temperature, linear power density and flow velocity. Implosive bubble formation and collapse are the main nature of subcooled boiling, and their behavior are the only sources to originate SBIV. Therefore, in order to explain the phenomenon of SBIV, it is essential to obtain reliable information about bubble behavior in subcooled boiling conditions. This was investigated at different conditions of coolant subcooling temperatures of 25 to 75°C, coolant flow velocities of 16 to 53 cm/s, and linear power densities of 100 to 600 W/cm. High speed photography at 13,500 frames per second was performed at these conditions. The results show that even at the highest subcooling condition, the absolute majority of bubbles collapse very close to the surface after detaching from the heating surface. Based on these observations, a simple model of surface tension and momentum change is introduced to offer a rough quantitative estimate of the force exerted on the heating surface. The formation of a typical bubble in subcooled boiling is predicted to exert an excitation force in the order of 10−4 N.

Investigation of Image Characteristics of Plume and Spatters during High-Power Disk Laser Welding

2013 ◽  
Vol 709 ◽  
pp. 301-304 ◽  
Author(s):  
Gui Qian Liu ◽  
Xiang Dong Gao
Keyword(s):  
Laser Welding ◽  
High Power ◽  
Laser Power ◽  
High Speed ◽  
Continuous Wave ◽  
Welding Process ◽  
Metal Vapor ◽  
High Speed Photography ◽  
Monitoring And Control ◽  
Disk Laser

During high-power laser welding process, the workpiece produces metal vapor because of the laser irradiation. The characteristics of metal vapor are related to the quality and stability of welding and the utilization of the laser power. An approach of analyzing the characteristics of metal vapor was researched during high-power disk laser bead-on-plate welding of Type 304 austenitic stainless steel plates at a continuous wave laser power of 10 kW. A high-speed photography was used to capture metal vapor dynamic images. Metal vapor area, beam path, swing angle are calculated by image processing, which is the foundation for monitoring and control of welding quality in real time.

INTERACTION OF TWO DIFFERENTLY SIZED BUBBLES IN A FREE FIELD

2012 ◽  
Vol 19 ◽  
pp. 180-184
Author(s):  
LUP WAI CHEW ◽  
BOO CHEONG KHOO ◽  
EVERT KLASEBOER ◽  
SIEW-WAN OHL
Keyword(s):  
High Speed ◽  
Free Field ◽  
Real Life ◽  
Separation Distance ◽  
Liquid Jets ◽  
Size Difference ◽  
High Speed Photography ◽  
Distinct Region ◽  
Bubble Interactions ◽  
Multiple Bubbles

The interaction between two different sized (spark created, non-equilibrium) bubbles is studied by using high speed photography. The bubble size ranges from 2 to 7 mm. The experimental results are compared to that of the similar sized bubbles reported in the literature. Interestingly, all the four major behaviors of bubble-bubble interactions (i.e. 'bubble-collapsed' induced liquid jets directed away from each other, liquid jets directed towards each other, bubble coalescence and the 'catapult' effect) are observed which bear much similarity to that found for similar sized bubbles' interaction. The main parameters studied/varied are the size of the bubbles, the dimensionless separation distance and the phase difference between the two bubbles. The results obtained are consistent with the cases of similar sized bubbles reported in the literature, with each type of behavior occupying a distinct region in the graphical plot. This indicates that the results for the (special) similar sized bubbles can be generalized to cases with different sized bubbles. Many of the real life applications such as cavitations corrosions often involve bubbles with significant size difference, thus the present findings are useful in predicting the behavior of multiple bubbles in many situations.

MULTIPLE SPARK-GENERATED BUBBLE INTERACTIONS

2009 ◽  
Vol 23 (03) ◽  
pp. 229-232 ◽  
Author(s):  
BOO CHEONG KHOO ◽  
DEEPAK ADIKHARI ◽  
SIEW WAN FONG ◽  
EVERT KLASEBOER
Keyword(s):  
High Speed ◽  
Bubble Surface ◽  
Solid Boundary ◽  
High Speed Photography ◽  
Bubble Interactions ◽  
Complex Interactions ◽  
Bubble Splitting ◽  
Shape Changes ◽  
Insight Into ◽  
Phase Differences

The complex interactions of two and three spark-generated bubbles are studied using high speed photography. The corresponding simulations are performed using a 3D Boundary Element Method (BEM) code. The bubbles generated are between 3 to 5 mm in radius, and they are either in-phase or out-of-phase with one another. The possible interaction phenomena between two identically sized bubbles are summarized. Depending on their relative distances and phase differences, they can coalesce, jet towards or away from one another, split into smaller bubbles, or 'catapult' away from one another. The 'catapult' effect can be utilized to generated high speed jet in the absence of a solid boundary or shockwave. Also three bubble interactions are highlighted. Complicated phenomena such as bubble forming an elliptical shape and bubble splitting are observed. The BEM simulations provide insight into the physics of the phenomena by providing details such as detailed bubble shape changes (experimental observations are limited by the temporal and spatial resolution), and jet velocity. It is noted that the well-tested BEM code [1,2] utilized here is computationally very efficient as compared to other full-domain methods since only the bubble surface is meshed.

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