scholarly journals Theory-assisted optical ray tracing to extract cavitation-bubble shapes from experiment

2021 ◽  
Vol 62 (3) ◽  
Author(s):  
Max Koch ◽  
Juan M. Rosselló ◽  
Christiane Lechner ◽  
Werner Lauterborn ◽  
Julian Eisener ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Cavitation Bubble ◽  
Bubble Dynamics ◽  
Solid Wall ◽  
Correction Method ◽  
Liquid Jets ◽  
Photographic Recording ◽  
Two Phase ◽  
Precise Shape ◽  
Optical Ray Tracing

AbstractExperimental analysis of cavitation bubble dynamics typically uses optical imaging and photographic recording. However, the images are often severely affected by distortions and shadows due to refraction and total reflection of the illuminating light at the liquid–gas interface of the bubble. Optical ray tracing may become a powerful tool for the analysis process by assisting in the comparison of experiments to numerical two-phase flow simulations. The novelty of the present approach consists in digitizing almost the complete experimental arrangement with all its optically relevant elements and objects—including a numerical model of the yet unknown bubble—and numerically photographing the scene via ray tracing. The method is applied to the jetting dynamics of single bubbles collapsing at a solid wall. Here, ray tracing can help in the interpretation of raw experimental data concerning the complex bubble interface deformations and internal structures during the collapse. The precise shape of the highly dynamical bubbles can be inferred, thus ray tracing provides a correction method for velocity values of the liquid jets. Strong evidence is found for the existence of an ultra-short-time, fast jet, exceeding velocities known to date in the field. Graphic abstract

Lattice Boltzmann Simulations of Bubble Dynamics at the Anode of a µDMFC

2005 ◽  
Author(s):  
Kai Fei ◽  
Chin-Hsien Cheng ◽  
Che-Wun Hong
Keyword(s):  
Pore Size ◽  
Flow Rate ◽  
Diffusion Layer ◽  
Lattice Boltzmann ◽  
Stream Flow ◽  
Bubble Dynamics ◽  
Model Simulation ◽  
Solid Wall ◽  
Two Phase ◽  
Flow Channels

This paper presents the bubble transport phenomenon at the anode of a micro direct methanol fuel cell (μDMFC) from a messooscopic viewpoint. Carbon dioxide bubbles generated at the anode may block part of the catalyst/diffusion layer and also the flow channels that cause the μDMFC malfunction. Lattice-Boltzmann methods (LBM) were employed in this paper to simulate the two phase flow in a simplified micro channel which emulates the bubble dynamics in the porous diffusion layer and the flow channel. A two-dimensional, nine velocity model (D2Q9) was established. The surface tension, buoyancy force were treated as source terms in the momentum equation. Bounce back boundary conditions were assumed at the fluid-solid interface in this model. Simulation results and parametric studies showed that the pore size, the stream flow rate and the hydrophilic effect between the fluid and the solid wall play the major roles in the bubble dynamics. Larger pore size, higher methanol stream flow rate and greater hydrophilicity are preferred for bubble removal at the anode diffusion layer and also the flow channels.

Bubble Dynamics Observed in a Gas-Liquid Venturi Flow

2011 ◽  
Author(s):  
Wataru Nishi ◽  
Masanori Nogami ◽  
Hiroyuki Takahira
Keyword(s):  
High Speed ◽  
Bubble Dynamics ◽  
Propagation Speed ◽  
Video Camera ◽  
Bubble Surface ◽  
Liquid Jets ◽  
Pressure Waves ◽  
Two Phase ◽  
Pressure Transducers ◽  
Two Bubbles

The present study deals with the experiments for the gas-liquid two-phase flow inside an acrylic Venturi tube using a high-speed video camera. Some interesting phenomena on the bubble dynamics are observed in the tube. First, the volume and surface oscillations of two interacting bubbles are observed in converging section of the tube when one bubble enters the throat. The volume oscillation of the bubble that enters the throat is caused by the detachment of the tip of the downstream surface of the bubble. The pressure wave irradiated from the bubble that enters the throat induces the volume and surface oscillations of the bubble that remains at the converging section. The parametric excitation is the reason for the surface oscillations. Second, the bubble deformations at the throat in a Venturi or a converging tube are investigated. The experiments show that two kinds of liquid jets are formed on the bubble surface; one is a forward jet that develops from the upstream surface to the downstream surface and the other is a counter jet in which the direction of the jet is opposite to the forward jet. It is shown that the counter jet occurs only when the distance between two bubbles in the throat is sufficiently short. The interactions between two bubbles cause the counter jet. It is also shown that the velocity of the forward jet becomes faster when the bubble is pinched off more upstream in the converging section. Finally, the propagations of the pressure waves are measured with pressure transducers. The impulsive pressure associated with the collapse of cavitation bubble cloud is measured when a bubble enters the throat of the tube. Also, the propagation speed of pressure waves is evaluated with the cross-correlation function. The results show that the propagation speed and damping of the pressure waves are dependent on the number density of bubbles at the downstream part in the tube.

Data assimilation for modeling cavitation bubble dynamics

2021 ◽  
Vol 62 (5) ◽  
Author(s):  
Javad Eshraghi ◽  
Arezoo M. Ardekani ◽  
Pavlos P. Vlachos
Keyword(s):  
Data Assimilation ◽  
Cavitation Bubble ◽  
Bubble Dynamics

scholarly journals Investigating Intense Rainfall Influence on Distance Measurement with a Time-of-Flight Camera Sensor Using Optical Ray-Tracing Simulation Technique

Proceedings ◽  
2018 ◽  
Vol 2 (13) ◽  
pp. 1056
Author(s):  
Marcus Baumgart ◽  
Norbert Druml ◽  
Markus Dielacher ◽  
Cristina Consani
Keyword(s):  
Ray Tracing ◽  
Time Of Flight ◽  
Autonomous Driving ◽  
Intense Rainfall ◽  
Signal Suppression ◽  
Tof Camera ◽  
Ray Tracing Simulation ◽  
Camera Sensors ◽  
Optical Ray Tracing ◽  
Rain Effect

Robust, fast and reliable examination of the surroundings is essential for further advancements in autonomous driving and robotics. Time-of-Flight (ToF) camera sensors are a key technology to measure surrounding objects and their distances on a pixel basis in real-time. Environmental effects, like rain in front of the sensor, can influence the distance accuracy of the sensor. Here we use an optical ray-tracing based procedure to examine the rain effect on the ToF image. Simulation results are presented for experimental rain droplet distributions, characteristic of intense rainfall at rates of 25 mm/h and 100 mm/h. The ray-tracing based simulation data and results serve as an input for developing and testing rain signal suppression strategies.

scholarly journals Bubble Dynamics in a Two-Phase Bubbly Mixture

2010 ◽  
Author(s):  
Arvind Jayaprakash ◽  
Sowmitra Singh ◽  
Georges Chahine
Keyword(s):  
Void Fraction ◽  
High Speed ◽  
Bubble Dynamics ◽  
Bubble Radius ◽  
Discharge Voltage ◽  
Large Bubble ◽  
Water Mixture ◽  
Two Phase ◽  
Mixture Density ◽  
Bubbly Medium

The dynamics of a primary relatively large bubble in a water mixture including very fine bubbles is investigated experimentally and the results are provided to several parallel on-going analytical and numerical approaches. The main/primary bubble is produced by an underwater spark discharge from two concentric electrodes placed in the bubbly medium, which is generated using electrolysis. A grid of thin perpendicular wires is used to generate bubble distributions of varying intensities. The size of the main bubble is controlled by the discharge voltage, the capacitors size, and the pressure imposed in the container. The size and concentration of the fine bubbles can be controlled by the electrolysis voltage, the length, diameter, and type of the wires, and also by the pressure imposed in the container. This enables parametric study of the factors controlling the dynamics of the primary bubble and development of relationships between the bubble characteristic quantities such as maximum bubble radius and bubble period and the characteristics of the surrounding two-phase medium: micro bubble sizes and void fraction. The dynamics of the main bubble and the mixture is observed using high speed video photography. The void fraction/density of the bubbly mixture in the fluid domain is measured as a function of time and space using image analysis of the high speed movies. The interaction between the primary bubble and the bubbly medium is analyzed using both field pressure measurements and high-speed videography. Parameters such as the primary bubble energy and the bubble mixture density (void fraction) are varied, and their effects studied. The experimental data is then compared to simple compressible equations employed for spherical bubbles including a modified Gilmore Equation. Suggestions for improvement of the modeling are then presented.

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