• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.14-17
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• 2008

Recently, several advanced flow visualization techniques such as Particle Image Velocimetry (PIV) including stereo PIV, holographic PIV, and dynamic PIV have been developed. These advanced techniques have strong potential as the experimental technology which can be used for verifying numerical simulation. In addition, there would be indispensable in solving complicated thermo-fluid flow problems not only in the industrial fields such as automotive, space, electronics, aero- and hydro-dynamics, steel, and information engineering, but also in the basic research fields of medical science, bio-medical engineering, environmental and energy engineering etc. Especially, NT Nano Technology) and BT (Bio Technology) strongly demand these advanced measurement techniques, because it is difficult for conventional methods to observe most complicated nano- and bio-fluidic phenomena. In this paper, the basic principle of these advanced visualization techniques and their practical applications which cannot be resolved by conventional methods, such as flow in automotive HVAC system, ship and propeller wake, three-dimensional flow measurement in micro-conduits, and flow around a circulating cylinder will be introduced.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.14-17
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• 2008

Recently, several advanced flow visualization techniques such as Particle Image Velocimetry (PIV) including stereo PIV, holographic PIV, and dynamic PIV have been developed. These advanced techniques have strong potential as the experimental technology which can be used for verifying numerical simulation. In addition, there would be indispensable in solving complicated thermo-fluid flow problems not only in the industrial fields such as automotive, space, electronics, aero- and hydro-dynamics, steel, and information engineering, but also in the basic research fields of medical science, bio-medical engineering, environmental and energy engineering etc. Especially, NT (Nano Technology) and BT (Bio Technology) strongly demand these advanced measurement techniques, because it is difficult for conventional methods to observe most complicated nano- and bio-fluidic phenomena. In this paper, the basic principle of these advanced visualization techniques and their practical applications which cannot be resolved by conventional methods, such as flow in automotive HVAC system, ship and propeller wake, three-dimensional flow measurement in micro-conduits, and flow around a circulating cylinder will be introduced.

• Journal of the Korean Society of Visualization
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• v.22 no.2
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• pp.44-54
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• 2024

This study investigates the effectiveness of using a plasma actuator for active control of turbulent flow around a finite square cylinder. The primary objective is to analyze the impact of plasma actuators on flow separation and wake region characteristics, which are critical for reducing drag and suppressing vortex-induced vibrations. Direct Numerical Simulation (DNS) was employed to explore the flow dynamics at various operational parameters, including different actuation frequencies and voltages. The proposed methodology employs a neural network trained using the Proximal Policy Optimization (PPO) algorithm to determine optimal control policies for plasma actuators. This network is integrated with a computational fluid dynamics (CFD) solver for real-time control. Results indicate that this deep reinforcement learning (DRL)-based strategy outperforms existing methods in controlling flow, demonstrating robustness and adaptability across various flow conditions, which highlights its potential for practical applications.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.454-459
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• 2003

The one of the most important subject to develop a LPDi engine is to suppress the generation of bubble inside LPG direct injector. For the purpose of this, in this study, the analogy visualization injector to visualize the generation and behavior of bubble, is manufactured and the bubbling phenomenon and behaviors are visualized and studied. The bubble inside the injector is generated at injection hole and after rising by buoyancy, it disappear around the top of a nozzle. The number of bubble generated is little changed regardless of the lapse of time but it is increased remarkably as the temperature around the injector is increased. With injection, the temperature around the injector at which the bubble is generated in_cylinder is much lower than that without injection because the transient pressure drop of fuel by injection.

• Journal of Mechanical Science and Technology
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• v.19 no.2
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• pp.704-715
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• 2005

In this study, to investigate in-cylinder tumble or swirl intake flow of a gasoline engine, the flow characteristics were examined with opening control valve (OCV) and several swirl control valves (SCV) which intensify intake flow through steady flow experiment, and also turbulent characteristics of in-cylinder flow field were investigated by 2-frame cross-correlation particle image velocimetry (PIV) method. In the investigation of intake turbulent characteristics using PIV method, the different flow characteristics were showed according to OCV or SCV figures. The OCV or SCV installed engine had higher vorticity and turbulent kinetic energy than a baseline engine, especially around the wall and lower part of the cylinder. Above all, SCV B type was superior to the others. About energy dissipation and reynolds shear stress distribution, a baseline engine had larger loss than OCV or SCV installed one because flow impinged on the cylinder wall. It should be concluded, from what has been said above, as swirl component was added to existing tumble flow adequately, it was confirmed that turbulent intensity was enlarged, flow energy was conserved effectively through the experiment. In other words, there is a suggestion that flow characteristics as these affected to in-cylinder combustion positively.

• International Journal of Automotive Technology
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• v.6 no.5
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• pp.453-460
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• 2005

The tumble or swirl flow is used to promote mixing of air and fuel in the cylinder and to enlarge turbulent intensity in the end of the compression stroke. Since the in-cylinder flow is a kind of transient state with rapid flow variation, which is non-steady state flow, the tumble or swirl flow has not been analyzed sufficiently whether they are applicable to combustion theoretically. In the investigation of intake turbulent characteristics using PIV method, typical flow characteristics were figured out by SCV configurations. An engine installed SCV had higher vorticity and turbulent strength by fluctuation and turbulent kinetic energy than a baseline engine, especially near the cylinder wall and lower part of the cylinder. Above all, the engine with SCV 8 was superior to the others in aspect of vorticity and turbulent strength. For energy dissipation, a baseline engine had much higher energy loss than the engine installed SCV because flow impinged on the cylinder wall. Consequently, as swirl flow was added to existing tumble flow, it was found that fluctuation increased and flow energy was conserved effectively through the experiment.

• 한국가시화정보학회:학술대회논문집
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• 2002.11a
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• pp.63-66
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• 2002

The Flow patterns around two cylinders in various arrangements were studied by a discrete vortex method. The flow for the surface of each cylinder was represented by arranging bound vortices at adequate intervals. The viscous diffusion of fluid was represented by the random walk method. The vortex distributions, streaklines, timelines and velocity vectors around two cylinders were calculated for centre-to-centre pitch rations of P/D=1.5 and 2.5, attack angles of $\alpha=0^{\circ},\;30^{\circ},\;60^{\circ},\;and\;90^{\circ}$, correspond to the photographs by flow visualization and the flow intereference between two cylinders in var ious arrangements was clearly visualized by a numerical simulation.

• International Journal of Automotive Technology
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• v.6 no.1
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• pp.1-8
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• 2005

Recently, the HSDI (High Speed Direct Injection) diesel engine has been spotlighted as a next generation engine because it has a good potential for high thermal efficiency and fuel economy. This study was carried out to investigate the in-cylinder flow characteristics generated in a HSDI diesel engine with a 4-valve type cylinder head. The four kinds of cylinder head were manufactured to elucidate the effect of intake port geometry on the in-cylinder flow characteristics. The steady flow characteristics such as coefficient of flow rate $(C_{f})$, swirl ratio (Rs), and mass flow rate (m,) were measured by the steady flow test rig and the unsteady flow velocity within a cylinder was measured by PIV. In addition, the in-cylinder flow patterns were visualized by the visualization experiment and these results were compared with simulation results calculated by the commercial CFD code. The steady flow test results indicated that the mass flow rate of the cylinder head with a short distance between the two intake ports is $13\%$ more than that of the other head. However, the non-dimensional swirl ratio is decreased by approximately $15\%$. As a result of in-cylinder flow characteristics obtained by PIV and CFD calculation, we found that the swirl center was eccentric from the cylinder center and the position of swirl center was changed with crank angle. As the piston moves to near the TDC, the swirl center corresponded to the cylinder center and the velocity distribution became uniform. In addition, the results of the calculation are in good agreement with the experimental results.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.2
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• pp.219-235
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• 2014

With the development of the technology of underwater moving bodies, the need for developing the knowledge of surface effect interaction of free surface and underwater moving bodies is increased. Hence, the two-phase flow is a subject which is interesting for many researchers all around the world. In this paper, the non-linear free surface deformations which occur during the water-exit of a circular cylinder due to its buoyancy are solved using finite volume discretization based code, and using Volume of Fluid (VOF) scheme for solving two phase flow. Dynamic mesh model is used to simulate dynamic motion of the cylinder. In addition, the effect of cylinder mass in presence of an external force is studied. Moreover, the oblique exit and entry of a circular cylinder with two exit angles is simulated. At last, water-exit of a circular cylinder in six degrees of freedom is simulated in 3D using parallel processing. The simulation errors of present work (using VOF method) for maximum velocity and height of a circular cylinder are less than the corresponding errors of level set method reported by previous researchers. Oblique exit shows interesting results; formation of waves caused by exit of the cylinder, wave motion in horizontal direction and the air trapped between the waves are observable. In 3D simulation the visualization of water motion on the top surface of the cylinder and the free surface breaking on the front and back faces of the 3D cylinder at the exit phase are observed which cannot be seen in 2D simulation. Comparing the results, 3D simulation shows better agreement with experimental data, specially in the maximum height position of the cylinder.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.11
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• pp.827-833
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• 2009

The present study numerically investigates three-dimensional laminar flow past a rotating circular cylinder placed in a uniform stream. For the purpose of a careful analysis of the modification of flow by the effect of the rotation on the flow, numerical simulations are performed at a various range of rotational coefficients ($0{\leq}{\alpha}{\leq}2.5$) at one Reynolds number of 300. As ${\alpha}$ increases, flow becomes stabilized and finally a steady state beyond the critical rotational coefficient. The 3D (three dimensional) wake mode of the stationary cylinder defined at this Reynolds number has been disorganized according to ${\alpha}$, which were observed by the visualization of 3D vortical structures. The variation of the Strouhal number is very weak when the wake pattern is changed according to the rotational coefficient. As ${\alpha}$ increases, the lift increases, whereas the drag decreases.