• 한국가시화정보학회:학술대회논문집
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• 2005.12a
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• pp.50-53
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• 2005

The turbulent flow around a sphere was investigated in a streamwise meridian plane using two experimental techniques: smoke-wire flow visualization in wind tunnel at Re=5,300 and PIV measurements in a circulating water channel at Re=7,400. The smoke-wire visualization shows flow separation points near an azimuthal angle of $90^{\circ}$, recirculating flow, transition from laminar to turbulent shear layer, evolving vortex roll-up and fully turbulent eddies in the sphere wake. In addition, the mean flow pattern extracted by particle tracing method in water tunnel at Re= 14,500 reveals two distinct comparable toroidal(not closed) vortices in the recirculation region. The mean velocity field measured using a PIV technique demonstrates the detailed wake configuration of close symmetric recirculation and near-wake configuration with two toroidal vortices, reversed velocity zone and vorticity contours.

• Fire Science and Engineering
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• v.15 no.1
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• pp.41-46
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• 2001

The flow induced by a vertically impinging circular jet under a horizontal plate is investigated by visualization technique, using kerosene smoke in nitrogen gas to visualize the vortex flow and impinging flow. The light source was the sheet beam of Ar-Ion laser. The vertical and horizontal images scattering of kerosene smoke were recorded by the high speed CCD camera and the video camera. The instantaneous velocity of the vortex and the mean velocity of the smoke front were measured from the acquisited images.

• Journal of the Korean Society of Visualization
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• v.8 no.3
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• pp.12-21
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• 2010

Swirling flows are found in very wide range of applications, for examples, cyclone separators, spraying machines, heat exchangers and jet pumps, ect. Relatively, little work has been done on the swirl flow using flow visualization techniques. This study deals with many visualization techniques to study on swirling flow. These techniques are related to oil films methods, smoke, dye liquids, liquid crystal, stroboscope light, smoke wire, white light, naphthalene sublimation, LDV(lase doppler Velocimetry) and PIV(particle image velocimetry). The present work has handled single, annular, carved tube, swirl expansion and swirl wake using several visualization methods in the vertical and horizontal circular tube.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.401-402
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• 2006

The turbulent flow around a sphere was investigated using two experimental techniques: smoke-wire flow visualization in wind tunnel at Re=5300, 11000 and PIV measurements in a circulating water channel. The smoke-wire visualization shows flow separation points near an azimuthal angle of $90^{\circ}$, recirculating flow, transition from laminar to turbulent shear layer, evolving vortex roll-up and fully turbulent eddies in the sphere wake. The mean velocity field measured using a PIV technique in x-y center plane demonstrates the detailed near-wake structure such as nearly symmetric recirculation region, two toroidal vortices, laminar separation, transition and turbulent eddies. The PIV measurements of turbulent wake in y-z planes show that a recirculating vortex pair dominates the near-wake region.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.12
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• pp.1017-1026
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• 2016

The present paper describes the two off-surface visualization techniques and their application examples to vortex flows. One of the two visualization techniques is the classical smoke-wire technique, and the other is the visualization technique using the micro water-droplets generated by the home-style ultrasonic humidifier. The smoke-wire technique has the limit of air flow speed (about 5 m/sec for 0.07 mm-diameter wire) and the pollution problem, but it produces very fine and clear streak line sheet. It is applied to visualize the wing-tip vortices of a 3-dimensional wing. The micro water-droplet technique has the larger limit of air flow speed (above 10 m/sec) and is free from pollution and toxic problems compared to the smoke-wire technique. It is successfully applied to visualize the complex vortex system of a double-delta wing with an apex strake.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.1
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• pp.71-77
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• 2001

A flow visualization study using the oil film method and the smoke-laser light sheet arrangement is carried out to investigate the three-dimensional flow pattern around the free end surface region of a finite circular cylinder (aspect ratios of 1.25 and 4.25) mounted on a flat plate. The experiment is performed for the cases of two Reynolds numbers: 5.92${\times}$10$^3$and 1.48${\times}$10(sup)5. Various kinds of singular points on the free-end surface are disclosed from the oil surface flow visualization. The smoke-laser light sheet visualization, to aid in understanding the oil streak-line patterns, clearly demonstrates that a pair of tornado-like vortices marched along the downstream together with a pair of side tip vortices. A topological sketch to characterize the surface flow and the four vortices emanating from the top surface is included.

• 한국가시화정보학회:학술대회논문집
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• 2005.12a
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• pp.64-68
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• 2005

In this study, the smoke flows of the inner subway station were visualized through a numerical analysis and visualization experiment in the subway fire. A transparent acrylic model was designed and installed as 1:25th scale-down as the actual subway station by using geometrical similarity The properties of subway fire were reconstructed according to Densimetric Froude Similarity. The 47 to 53 ratio of the mixed air and Helium was inputted in the inner acrylic model to describe 1MW fire intensity with reference to the experiment paper. For the same time, the fire smoke from a smoke generator was inputted in the inner acrylic model with the mixture. At this time, the buoyancy effect of Helium gas went up the smoke to the acrylic model. When the sheet beam of Ar-lon laser was given out to the top and stair of subway model, the digital camcorder took the images of the scattered cluster of smoke particles when applying the smoke management system and PSD.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.1
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• pp.55-62
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• 2002

A new off-surface visualization method of using the micro water droplet and laser beam sheet was presented. About a size of 5 to TEX>$10\mu\textrm{m}$ micro water droplet could be made from home-style ultrasonic humidifier, A 3 W Argon ion laser and cylindrical lens were used to generate a laser beam sheet, which interrogate specific cross section of the vortical flow field. Application of this new visualization method was conducted in KAFA small-sized low speed wind tunnel of having the test section of 0TEX>$0.9 m(W){\times}$0.9 m(H){\times}2.1 m(L)$$$. Visualization results show this method relatively easy and safe flow visualization method for wind tunnel testing. Moreover, this method is also make up for the disadvantage of smoke visualization, and can be applied to higher flow velocity range than that of smoke visualization.

• Journal of the Korean Society of Visualization
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• v.11 no.2
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• pp.34-40
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• 2013

A flow visualization near submerged nozzle of solid rocket motor was conducted by experiments. A numerical simulation was also performed to reveal detailed phenomena. Radial cold flow simulating hot gas was introduced by a porous grain model which was manufactured by perforated steel plates. The grain model was mounted in high-pressure chamber which has quartz glass at the top of the grain model. From the high-speed images, a rotating vortex was observed and the two type of counter-rotating momentums were generated in numerical results. The rotating momentum was generated at the fin-slot grain because of unbalance between high-velocity flow from slots and low-velocity flow from fin-bases. As a result, roll torques can be produced by the rotating vortex tube.

• 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.