• Water for future
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• v.31 no.4
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• pp.291-297
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• 1998

The two dimensional time dependent flow past a circular cylinder is analyzed numerically. In the analysis, equations of conservation of mass and momentum are transformed to equations of stream function-vorticity and vorticity transport, and nondimensionalized by nondimensional parameters representing flow characteristics, The resulting stream function-vorticity equation and vorticity transport equation are solved by successive over relaxation scheme and alternating direct implicit scheme. Numerical experiments are performed for the flow in the range of Reynolds number 125 to 275. The time dependent streamlines, vorticities, pressure on cylinder surface, separation angle, and drag and lift coefficients are calculated, and the method for estimation of pressure on cylinder surface and the outer boundary limit are developed.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.1
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• pp.42-49
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• 2015

The pressure oscillation induced by inhibitor in a solid rocket motor has been investigated by 3D large eddy simulation(LES) and proper orthogonal decomposition(POD). The vortex generation and breakdown at inhibitor are periodically observed between the inhibitor and the nozzle by flow-acoustic coupling mechanism. The excitation of pressure oscillation occurs as the flow impinges on the submerged nozzle head which recirculate in the cavity in rear dome of the motor chamber. The vortex generation frequency is closely related with the shedding frequencies of the detached vorticities at the inhibiter, which fairly compared with the experimental data.

• Journal of Environmental Science International
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• v.21 no.11
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• pp.1395-1406
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• 2012

The purpose of this study is to analyze the hydraulic characteristics of the ice-harbor fishway by considering its geometrical form and utilize such analysis results as the foundational database to be used when establishing fishways in the future. first of all, the study realizes the same form as an ice-harbor fishway that is currently implemented via a FLOW-3D model and estimated the parameters that were optimal to the numerical mock test. Then, this study analyzed the level of sensitivity of the flow conditions which fluctuated due to the changes in geometrical changes by adjusting the inclination and pocket spacing by using the estimated optimal parameters. As a result, the study arrived at the following conclusions. The vortical velocity increased and had a significant effect on the inclination of the fishway. Furthermore, as the velocity within the vorticity increased due to the narrowed vortical area, it was determined that further studies on vorticities or the determination of the design method for the decrease in vortical velocity were imperative.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.209-215
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• 2001

The head-capacity curves for pumps developed by the pump manufacturer are based on tests of a single pump operating in a semi-infinite pool with no nearby walls or floors and no stray currents, Hence, flow into the Pump suction is symmetrical with no vortices or swirling. Pump station designers rely on these curves to define the operating conditions for the pump selected. But various constraints such as size, cost, and limitations on storage time require walls, floors, and pump intakes to be close proximity to each other. From this background, the authors are carrying out a systematic study on the flow characteristics of intakes within a sump found in pump stations. Model pump intake basin is designed and PIV is adopted as a measuring tool to capture the instantaneous flow patterns. Special attention is paid to investigate the flow patterns near the free surface, side-wall and back-wall due to different clearances from back-wall to vertical in take pipe. Moreover, the locations and vorticities of the various types of vortices that were found in the examinations are discussed.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.2151-2156
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• 2003

The distinguishing features of flows at high angles of attacks are caused by the generation of free shear layers at sharp leading edges, by separation of the viscous layers from the surfaces of wings and bodies and by the flow in the wakes of the wings and bodies. In this study, systematic approach by PIV experimental method within a circulating water channel was adopted to study the fundamental characteristics of induced vortex generation, development and its breakdown appearing on a delta wing model with or without LEX in terms of four angles of attack($15^{\circ}$, $20^{\circ}$, $25^{\circ}$, $30^{\circ}$) and six measuring sections(30%, 40%, 50%, 60%, 70%, 80%) of chord length. Distributions of time-averaged velocity vectors and vorticities over the delta wing model were compared along the chord length direction. Highly swept leading edge extension(LEX) applied to delta wings has greatly improved the subsonic maneuverability of contemporary fighters. High-speed CCD camera which made it possible to acquire serial images is able to get the detailed information about the flow characteristics occurred on the delta wing. Especially quantitative comparison of the maximum vorticity featuring the induced pressure distribution were also conducted to clarity the significance of the LEX existence.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.563-569
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• 2001

The head-capacity curves for pumps developed by the pump manufacturer are based on tests of a single pump operating in a semi-infinite pool with no nearby walls or floors and no stray currents, Hence, flow into the pump suction is symmetrical with no vortices or swirling. Pump station designers rely on these curves to define the operating conditions for the pump selected. But various constraints such as size, cost, and limitations on storage time require walls, floors, and pump intakes to be close proximity to each other. From this background, the authors are carrying out a systematic study on the flow characteristics of intakes within a sump found in pump stations. Model pump intake basin is designed and PIV is adopted as a measuring tool to capture the instantaneous flow patterns. Special attention is paid to investigate the flow patterns near the free surface, side-wall and back-wall due to different clearances from back-wall to vertical in take pipe. Moreover, the locations and vorticities of the various types of vortices that were found in the examinations are discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.8
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• pp.1068-1076
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• 2001

The relations between wall pressure fluctuations and near-wall streamwise vortices are investigated in a spatially-developing turbulent boundary layer using the direct numerical simulation. The power spectra and two-point correlations of wall pressure fluctuations are presented to validate the present simulation. Emphasis is placed on the identification of the correlation between wall pressure fluctuations and streamwise vorticities. It is shown that wall pressure fluctuations are directly linked with the upstream streamwise vortices in the buffer region of the turbulent boundary layer. The maximum correlation occurs with the spanwise displacement from the location of wall pressure fluctuations. The conditionally-averaged vorticity field and the quadrant analysis of Reynolds shear stress indicate that the sweep events due to streamwise vortices generate positive wall pressure fluctuations, while negative wall pressure fluctuations are created beneath the ejection events and vortex cores. The instantaneous flow field and time records reveal that the rise of high wall pressure fluctuations coincide with the passages of the upstream streamwise vortices.

• Journal of the Korean Society of Visualization
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• v.8 no.1
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• pp.39-45
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• 2010

The optimal design is needed for the blade geometry of the quad-rotor blades which is mainly used for Unmanned Aerial Vehicle. To do this, it is important to analyze the wakes under the blades. In the present study, the flow around the rotating blades was analyzed using PIV(Particle Image Velocimetry) and CFD(Computational Fluid Dynamics). The maximum axial velocity was measured at about 60% position toward the radial direction of the blade. The positions of vorticities in the test section obtained by PIV and CFD were turned out to be almost alike. The values in the difference of pressure coefficients at the upper and the lower blades were increased depending on the radial direction. Then, the values were decreased at the blade tip. The data of the flow analysis in the present study are expected to be served as the design of blades and ducts for the thrust improvement in the future.

• Ocean and Polar Research
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• v.21 no.2
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• pp.99-108
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• 1999

With sectional data obtained in September of 1987, 1988 and 1989 by quadrireciprocal ADCP measurement and CTD cast, the current structure, volume transport and vorticity in the Western Channel of the Korea Strait were studied. The characteristics of Tsushima Current water persisted throughout the summer especially in the homogeneous water of temperature $14-16^{\circ}C$ located at the depth of 50-100m below seasonal termocline. Thickness and velocity of the homogeneous layer are about 10-170m and 20-60cm/s. and the relative vorticity for this layer is shown to be nearly constant and it is smaller than the planetary vorticity. Potential vorticity of $2.70-7.10{\times}10^{-6}m^{-1}s^{-1}$ is found to be dependent mainly on planetary rather than on the relative vorticities. The Tsushima Current water represented by the homogeneous layer R14-16^{\circ}C$ may keep the potential vorticity at the area of strong current in the Strait. The ADCP current structure is similar to geostrophic current and the core of the current with the speed of 30-50cm/s is situated in the middle layer over the deep trough. With large tidal fluctuation the volume transport has mean value of 1.17sv which was about 40% larger than that of geostrophic calculation.

• 한국가시화정보학회:학술대회논문집
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• 2002.11a
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• pp.105-108
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• 2002

Highly swept leading edge extension(LEX) applied to delta wings has greatly improved the subsonic maneuverability of contemporary fighters. In this study, systematic approach by PIV experimental method within a circulating water channel was adopted to study the fundamental characteristics of induced vortex generation, development and its breakdown appearing on a delta wing model with or without LEX in terms of four angles of attack$(15^{\circ},\;20^{\circ},\;25^{\circ},\;30^{\circ})$ and six measuring sections$(30\%,\;40\%,\;50\%,\;60\%,\;70\%,\;80\%)$ of chord length. Distributions of time-averaged velocity vectors and vorticities over the delta wing model were compared along the chord length direction. High-speed CCD camera which made it possible to acquire serial images is able to get the detailed information about the flow characteristics occurred on the delta wing. Especially quantitative comparison of the maximum vorticity featuring the induced pressure distribution were also conducted to clarity the significance of the LEX existence.