• Journal of the Korean Society of Visualization
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• v.1 no.2
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• pp.38-46
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• 2003

An experimental investigation was performed to study the turbulent characteristics of swirling flow a 90$^{\circ}C$ circular tube for Re = 10,000, 15,000 and 20,000. 2D-PIV(Particle Image Velocimetry)technique was employed to measure the fluctuation velocity field. The results include spatial distributions of mean velocity vectors, turbulence intensity and turbulence kinetic energy. The axial and radial turbulence intensities, and kinetic energy profiles show double-peak structures in the inlet region of the 90 degree bend and the profiles are disappeared along the test tube with decaying the swirl intensity.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2771-2788
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• 2020

Experiments are conducted to study bubble flow behavior during the instability of subcooled boiling under uniform and non-uniform transverse heating. The non-uniform heat distribution introduces nonuniform bubble generation and condensation rates on the heated surface, which is different from the uniform heating. These bubble generation and condensation characteristics introduce a non-uniform local pressure distribution in the transverse direction, which creates an extra non-uniform pressure on the flowing bubbles. Therefore, different bubble flow behavior can be observed between uniform and non-uniform heating conditions. In the uniform heating, bubble velocity fluctuations are low, and the bubbles travel straight along the axial direction. In the non-uniform heating, more fluctuation in the bubble velocity occurs at low mass flow rate and high subcooled inlet temperatures, and reverse flow is observed. Additionally, the bubbles show a zigzag trajectory when they pass through the channel, which indicates the existence of cross flow in the transverse direction.

• Tribology and Lubricants
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• v.11 no.2
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• pp.63-70
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• 1995

The analytical design method of gerotor profile, based on an envelope of a family of curves, is proposed. Analysis to calculate the flow rate and the torque capacity of a gerotor set are presented. The influence of the circular tooth radius and the amount of eccentricity on the configuration of a gerotor has been explored in this paper. The variation of the inlet volume and the fluctuation of the generated torque are also analyzed.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.290-295
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• 2000

An experimental study was carried out in a cavity with upper channel and square heat surface by visualization equipment with Mach-Zehnder interferometer and laser apparatus. The visualization system consists of 2-dimensional sheet light by Argon-Ion Laser with cylindrical lens and flow picture recording system. Instant simultaneous velocity vectors at whole field were measured by 2-D PIV system(CACTUS'2000). Obtained result showed various flow patterns. Severe unsteady flow fluctuation within the cavity are remarkable and sheared mixing layer phenomena are also found at the region where inlet flow is collided with the counter-clockwise rotating main primary vortex. Photographs of Mach-Zehnder are also compared in terms of constant heat flux.

• Nuclear Engineering and Technology
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• v.27 no.5
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• pp.710-720
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• 1995

The propagation of pump-induced pressure pulsation in a reactor is important because of the potential for vibration and resultant damage of reactor internals. A hydrodynamic model has been developed to obtain the pressure fluctuation due to the operation of pumps in the annulus(between the core support barrel and reactor vessel of a pressurized water reactor) including the coolant inlet pipe. The mathematical analysis is formulated in accordance with the linearized Navier-Stokes equation by assuming a compressible, inviscid flow. Two regions are considered separately and by coupling the solutions of the inlet pipe and the annulus, the inlet nozzle pressure(pressure at pipe and annulus interface) is to be calculated without assumptions. The geometric parameter effect on the pump-induced pressure pulsation is evaluated. Comparison of predicted and measured inlet nozzle pressure values for each forcing frequency shows good order of magnitude agreement.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.2
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• pp.197-204
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• 2018

In the present study, unsteady flow analysis has been conducted to investigate the blade forces and wake flow around a hybrid street-lamp having a vertical-axis small wind turbine and a photovoltaic panel. Uniform velocities of 3, 5 and 7 m/s are applied as inlet boundary condition. Relatively large vortex shedding is formed at the wake region of the photovoltaic panel, which affects the increase of blade torque and wake flow downstream of the wind turbine. It is found that blade force has a good relation to the variation of the angle of attack with the rotation of turbine blades. Variations in the torque on the turbine blade over time create a cyclic fluctuation, which can be a source of turbine vibration and noise. Unsteady fluctuation of blade forces is also analyzed to understand the nature of the vibration of a small wind turbine over time. The detailed flow field inside the turbine blades is analyzed and discussed.

• Journal of the Korean Society of Visualization
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• v.9 no.4
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• pp.16-21
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• 2011

The effects of stroke change on turbulent kinetic energy for the in-cylinder flow of a four-valve SI engine were studied. For this study, the same intake manifold, head, cylinder, and the piston were used to examine turbulence characteristics in two different strokes. In-cylinder flow measurements were conducted using three dimensional LDV system. The measurement method, which simultaneously collects 3-D velocity data, allowed a evaluation of turbulent kinetic energy inside a cylinder. High levels of turbulent kinetic energy were found in regions of high shear flow, attributed to the collisions of intake flows. These specific results support the more general conclusion that the inlet conditions play the dominant role in the generation of the turbulence fields during the intake stroke. However, in the absence of two counter rotating vortices, this intake generated turbulent kinetic energy continues to decrease but at a much faster rate.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.4
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• pp.446-451
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• 2020

Flow induced vibration in a heat exchanger may cause damage to piping. The purpose of this study was to compare the characteristics of vortex shedding behavior through the circular tube banks at several tube locations, No.1, No. 10, and No. 19, with respect to time when the flow velocity of the inlet is constantly and periodically fluctuating.(60) The time characteristics of lift and the PSD characteristics were also investigated. In the case of periodic inlet flow velocity, strong vortex occurred at some time and after that time, a weak vortex was generated through the tube banks simultaneously. In the case of constant inlet flow velocity, the lift fluctuating frequency was 37.25Hz and that at the No. 19 tube was 18.63Hz and near 50Hz. In the case of periodic inlet flow velocity, the lift fluctuating frequency was 37.25Hz and 18.63Hz. The lift fluctuating frequency at No. 19 tube was observed broadly from 20Hz and 50Hz.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.1
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• pp.78-85
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• 1991

An experimental result for heat transfer of pulsating turbulent pipe flow was presented under the condition of fully developed dynamic regime and uniform wall heat flux. Experiments were performed at following conditions ; Inlet time-averaged Reynolds number varied from 5000 to 11000; The peak pressure fluctuation were 1.3, 2.3 and 3.5 percent of the mean pressure; Pulsating frequency ranged from 53 Hz to 320 Hz The measurements showed that the effect of pulsation on local heat transfer is greater at downstream, in which pulsating source exists, than upstream and the heat transfer rate, averaged over the pipe length, was higher or lower than in an equivalent non-pulsating flow according to the pulsating conditions. In addition, the significant change of heat transfer rate was observed in acoustically resonant conditions, when the pulsating frequency of the flow corresponded to the pipe natural frequency.

• Solar Energy
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• v.20 no.4
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• pp.53-60
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• 2000

An experimental study was carried out in a cavity with upper channel and square heat surface by visualization equipment with Mach-Zehnder interferometer and laser apparatus. The visualization system consists of 2-dimensional sheet light by Argon-Ion Laser with cylindrical lens and flow picture recording system. Instant simultaneous velocity vectors at whole field were measured by 2-D PIV system(CACTUS'2000). Obtained result showed various flow patterns. Severe unsteady flow fluctuation within the cavity are remarkable and sheared mixing layer phenomena are also found at the region where inlet flow is collided with the counter-clockwise rotating main primary vortex. Photographs of Mach-Zehnder are also compared in terms of constant heat flux.