• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.27-30
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• 2002

The particle velocity in superfluid helium (He II) induced by a gas dynamic shock wave impingement onto He II free surface were studied experimentally by using Schlieren visualization method with an ultra-high speed video camera. It is found form visualization results that a dark zone in the immediate vicinity of the vapor-He II interface region is formed because of the high compressibility of He II and is developed toward bulk He II with the flowing-down speed of the vapor-He II interface. The mass velocity behind a transmitted compression shock wave that is equal to the contraction speed of He II amounts to 10 m/sec, the Reynolds number of which reaches $10^{7}$. This fact suggests that the superfluid shock tube facility can be applied to an experimental facility for high Reynols number flow as an alternative to the superfluid wind tunnel.

• Journal of ILASS-Korea
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• v.5 no.1
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• pp.49-57
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• 2000

This study presents the flow visualization results, velocity and turbulence intensity measurements made within an air filter cover and entry region of a mass air flow sensor (MAFS) which is used in an induction system of 3.8L engine. Flow structure in two air filter cover assemblies were examined. The first was a clear plastic replica of the production cover while the second was a modified clear plastic cover with a geometry configured to reduce fluctuations. High speed flow visualization and laser doppler velocimetry (LDV) systems were used to reveal and analyze the flow field characteristics encountered in the sensor design process under steady flow conditions. A 40-watt copper vapor laser was used as a light source. Its beam is focused down to a sheet of light approximately 1.5mm thick. The light scattered off the particles was recorded by a 16mm high speed rotating prism camera at 5000 frames per second. A comparison of the flow patterns and LDV measurements in the original and modified air filter covers is presented to illustrate the controlling effect of the cover design on the turbulence structure formation near the bypass and on the sensor output signal. In both axial and radial planes of the main passage it was found that the turbulence flow pattern is remarkably influenced by the air filter cover and main passage configuration.

• Journal of the Korean Society of Visualization
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• v.8 no.2
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• pp.16-22
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• 2010

A flow visualization has been conducted to investigate unsteady flight characteristics of a model of dragonfly. The mechanism of lift generation by flapping wings is analyzed using smoke-wire and high speed camera. The experimental results of flow visualization show a discernible sequential dynamics that three mechanisms and high incidence angle of the wings are responsible for the lift generation. The leading edge vortex by the rapid acceleration of leading edge of the wing during initial stage of stroke causes a strong lift enhancement. Delayed stall during the stroke, fast supination and pronation of the wing near the end of each stroke are also responsible for the lift generation.

• Journal of the Korean Society of Visualization
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• v.11 no.3
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• pp.12-16
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• 2013

The impact and spreading behaviors of silicon dioxide nanoparticle colloidal suspension droplets were quantitatively visualized using a high-speed imaging system. Millimeter-scale droplets were generated by a syringe pump and a needle. Droplets of different velocity were impacted on a non-porous solid surface. Images were consecutively recorded using a CMOS high-speed camera at 5000 fps (frames per second) for millimeter-scale droplets. Temporal variations of droplet diameter, velocity and maximum spreading diameters were evaluated from the sequential images captured for each experimental condition. Effects of Reynolds number, Weber number, and particle concentration were investigated experimentally.

• Journal of the Korean Society of Visualization
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• v.21 no.3
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• pp.85-92
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• 2023

In this study, we present experimental results of cavitating flow around a vortex generator which is used to improve the flow in the wake of ships and enhance propulsion efficiency. We conducted experiments at the CNU cavitation tunnel on a total of six vortex generators, two different aspect ratios and three taper ratios. We recorded cavity patterns using a high-speed camera and quantitatively evaluated cavity fraction using OpenCV. The most important finding of this study is that the vortex cavity generated at a root leading edge of the vortex generator develops at a specific angle.

• Journal of the Korean Society of Visualization
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• v.22 no.2
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• pp.82-89
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• 2024

In this study, experiments were conducted to visualize and analyze the dynamic characteristics of splash and residual liquid film formation during and after the injection of water droplets onto vertically situated solid substrates with varying surface wettability, elasticity, and microtexture. As wettability decreased (higher contact angle), more splash droplets formed, and the residual liquid film decreased. Low contact angles resulted in thin residual films and less splash. Surface elasticity absorbed the impact forces of droplets, thereby decreasing splash phenomena and significantly reducing the formation of residual liquid films due to surface vibration. Surfaces with microtextures demonstrated control over droplet splash direction, guiding the liquid along desired pathways. High-speed imaging provided detailed insights, showing that surface properties critically influence splash dynamics and residual liquid film formation.

• Journal of the Korean Society of Visualization
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• v.16 no.3
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• pp.8-15
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• 2018

Recently, as the high speed railway becomes more common, new environmental problems such as noise around tunnels are appearing. When a high speed train enters a tunnel, a compression wave in the tunnel is generated and propagated toward the tunnel exit at a sonic speed. When it reaches the tunnel exit, a part of compression wave radiates as a pulse typed impulse wave to the outside of tunnel. The impulse wave has an explosive noise. When the impulse wave is propagated around a village, it induces a serious noise or other problems to the resident. In order to solve these engineering problems, it is important to investigate the radiation characteristics of the impulse wave radiated from the tunnel exit. In this study, the effect of the length and angle of the baffle plate at the tunnel exit on the impulse wave radiated from the tunnel exit was investigated by numerical analysis. As a results, the baffle plate greatly affected the propagation of impulse wave.

• Journal of the Korean Society of Visualization
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• v.8 no.4
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• pp.48-53
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• 2010

Water-uptake through roots, is an essential process of the water flow in plants. Its visualization is very useful for understanding sap flow dynamics at whole plant level. In this study, the tips of Arabidopsis' root hairs were excised and exposed to repeated dehydration and rehydration processes. The water-refilling through individual xylem vessels was visualized using the synchrotron X-ray micro-imaging technique. The high temporal resolution ($2\;{\mu}m$) and beam intensity of the X-ray source allowed to acquisition of consecutive X-ray images of the water-refilling process up to 10 frames/sec. Various flow patterns were observed and the ascending speed of the water-air interfaces was analyzed. The relation between the water-rising height and ascending speed was also analyzed. The present results would provide better alternative for investigating sap flows in roots.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.215-218
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• 2014

High combustion efficiency of hydrogen could make it an ideal source of green energy in the future. At this time, high pressure vessel is the most reasonable method of storing hydrogen. However, such a high pressurized vessel could pose a critical threat if ruptured. For this reason, it is important to understand the mechanism of hydrogen's self-ignition when a high-pressure hydrogen released into air. This paper presents several visualization images as experimental results using high-speed camera. From the visualization images, the ignition is initiated near rupture disk immediately after failure of disk. And the initial ignition and flame is stronger as a rupture pressure increases. However, this ignition region do not affect the general self-ignition mechanism when a high-pressure hydrogen is released into air through tue after failure of disk.

• Journal of the Korean Society of Visualization
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• v.16 no.1
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• pp.54-60
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• 2018

It is important to develop more efficient and productive casting processes for an automated high precision molten-metal casting system. Detailed analysis of molten-metal flow in the casting process by the numerical approach will help to optimize the control of a ladle. In this study, the smoothed particle hydrodynamics method was applied to analyze casting flow characteristics with different tilting angular speed and initial molten-metal level. The smoothed particle hydrodynamics technique has advantages to easily handle non-linear free surface behavior with the absence of a computational mesh. We found that tilting angular speed has relatively greater effect on the casting flowrate and that the effect of the initial molten-metal level is only minor. Further extensive study will be necessary to find an optimal condition for high efficient casting system.