• 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.

• 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.

• 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 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.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.7
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• pp.879-888
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• 2003

Swirling air flow in a horizontal round tube was experimentally studied for its visualization. The present investigation deals with swirl angle, flow visualization studies and accompanying vortex core behavior by using oil smoke and a hot wire anemometer for Re = 40,000 and 50000 at X/D = 41, 59 and 71. In the swirl air flow, a vortex core was formed at high swirl intensity along the test tube. The swirl angle and the vortex core depended on the swirl intensity along the test tube. The results of swirl angles measured by flow visualization and hot wire reasonably agree with those of previous studies.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.2 no.4
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• pp.82-87
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• 2003

Flow angle with Swirl in a horizontal circular tube and a cylindrical annuli were experimentally studied for its visualization. This present investigation deals with flow angle, flow visualization studies and vortex core by using oil smoke and a hot wire anemometer for Re = 40,000 and 50000 at X/D = 41, 59 and 71 in a horizontal circular tube. In the swirl air flow, a vortex core was formed at high swirl intensity along the test tube. The flow angle and the vortex core depended on the swirl intensity along the test tube. The results of flow angles with swirl measured by flow visualization and hot wire reasonably agree with those of Sparrow One of the primary objectives of this research was to measure the flow angle with swirl in a cylindrical annuli along the test tube for different Reynolds numbers. The Reynolds number for these measurements ranged from 60,000 to 100,000 with L/D = a to 4.

• Journal of the Korean Society of Visualization
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• v.4 no.2
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• pp.51-58
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• 2006

A boundary layer visualization was carried out in order to investigate the influence of Reynolds number on an oscillating airfoil. An NACA 0012 airfoil is sinusoidally pitched at the quarter chord point with oscillation amplitude of ${\pm}6^{\circ}$. A smoke-wire technique was employed to visualize the boundary layer and the near-wake. The freestream velocities are 1.98, 2.83 and 4.03m/s and corresponding chord Reynolds numbers are $2.3{\times}10^4,\;3.3{\times}10^4$, and $4.8{\times}10^4$, respectively. As the reduced frequency of K=0.1 is fixed, the corresponding frequency of an airfoil was adjusted in each case. The results reveal that the point at which the shear stress in an unsteady boundary layer separation disappears does not correspond with the position of the breakdown of the boundary layer, and that the breakdown of the boundary layer occurs further downstream.

• 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.7 no.2
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• pp.28-34
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• 2010

Two turbulent jet with different sinusoidal nozzle exit configurations of in-phase and $180^{\circ}$ out-of-phase were investigated experimentally using a smoke-wire method and a hot-wire anemometry. Mean velocity and turbulence intensity were measured at several downstream locations under $Re_D\;=\;5000$. For the case of in-phase nozzle configuration, the length of potential core exhibits negligible difference with respect to the transverse locations (0, $\lambda/4$ and $\lambda/2$), similar to that of a plane jet. On the other hand, a maximum difference of 30% in the potential-core length occurs for the $180^{\circ}$ out-of-phase configuration. The spatial distributions of turbulence intensities also show significant difference for the nozzle of $180^{\circ}$ out-of-phase, whereas non-symmetric distribution is observed in the near-exit region(x/D = 1) for the in-phase sinusoidal nozzle jet. Compared to a slit planc jet, the sinusoidal nozzle jets seem to suppress the velocity deficit as the flow goes downstream. The sinusoidal nozzle jet was found to decrease turbulent intensity dramatically. The flow visualization results show that the flow characteristics of the sinusoidal nozzle jet are quite different from those of the slit plane jet.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.2
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• pp.218-225
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• 1999

Flow visualization study has been conducted to simulate the turbulent dispersion behavior of a crossflow jet physically under the conditions of various thermal stratification in a wind tunnel. A smoke jet with the constant ratio of the jet to freestream velocity is injected normally to the cross flow of the thermally stratified wind tunnel(TSWT) for flow visualization. The typical natures of the smoke dispersion under different thermal stratifications such as neutral, weakly stable, strongly stable, weakly unstable, strongly unstable and inversion layer are successfully reproduced in the TSWT. The Instantaneous velocity and temperature fluctuations are measured by using a cold and hot-wire combination probe. The time averaged dispersion behaviors, the centerline trajectories, the spreading angles and the virtual origins of the cross jet are deduced from the edge detected images with respect to the stability parameter. All the general characteristics of the turbulent dispersion behavior reveal that the definitely different dispersion mechanisms are inherent in both stable and unstable conditions. It is conjectured that the turbulent statistics obtained in the various stability conditions quantitatively demonstrate the vertical scalar flux plays a key role in the turbulent dispersion behavior.