• Korean Journal of Optics and Photonics
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• v.11 no.4
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• pp.250-254
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• 2000

We have constructed laser Doppler velocimetry system using self-mixing effect with a semiconductor laser. This technology is based on the frequency mixing phenomena which occurs when light scattered back from the moving object into the laser cavity interferes with light inside the laser. We have compared the value of Doppler shifted frequency with the velocity variation of the wheel. Frequency dependence on the angle between the moving direction of rotating aluminum wheel and the incident beam also have been proved. As an illustration of the performance of the velocimeter, velocity measurements of a rotating disk are described. Doppler signal shows a good linear relationship with velocity of rotating disk.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.6
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• pp.175-183
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• 2010

In this study, laboratory experiments are conducted to investigate flow-fields around floating breakwaters by using the LDV(Laser Doppler Velocimetry) system. The LDV system is a well-known equipment to measure fluid particle velocities in laboratory experiments. Although the system requires great efforts and enormous time for measurements, it can provide precise velocity fields comparing to other available equipments. Various types of drafts and shapes for breakwaters are employed in laboratory experiments to analyze a relation between flow-fields and vorticity. A series of numerical experiments are also carried out by using a two-dimensional Navier-Stokes equations model. Numerically predicted results are compared with laboratory measurements.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.2
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• pp.156-163
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• 2001

The experiment is conducted on the rapidly rotating incompressible flow within a confined cylinder using LDV(Laser Doppler Velocimetry). The configurations of interest are the flows between a rotating upper disk with a bar and a stationary lower disk enclosed within a cylinder. The flow is considered to be an axisymmetric undisturbed basic flow. The results show that the flow is strongly dependent on the radius and the shape of bar but is negligibly affected by the Reynolds number in turbulent flow. It is observed that in the lid-driven case the main forms near the wall as the Reynolds number increases. The thin bar causes the second axial flow due to the suction effect and the thick bar causes the main flow to be pulled toward the surface of the bar. The step bar shows the dual effect of the two. 1:2 tilt bar shows that the main flow distributes wider than the other cases in which interference occurs due step bar.

• International Journal of Automotive Technology
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• v.7 no.3
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• pp.289-294
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• 2006

Better fundamental understanding of the interactions between the in-cylinder flows and combustion process is an important requirement for further improvement in the fuel economy and emissions of internal combustion(IC) engines. Flow near a spark plug at the time of ignition plays an important role for early flame kernel development(EFKD). Velocity data measurements in this study were made with a two-component laser Doppler velocimetry(LDV) near a spark plug in a single cylinder optical spark ignition(SI) engine with a heart-shaped combustion chamber. LDV velocity data were collected on an individual cycle basis under wide-open motored conditions with an engine speed of 1,000rpm. This study examines and compares the flow fields as interpreted through ensemble, cyclic and discrete wavelet transformation(DWT) analysis. The energy distributions in the non-stationary engine flows are also investigated over crank angle phase and frequency through continuous wavelet transformation(CWT) for a position near a spark plug. Wavelet analysis is appropriate for analyzing the flow fields in engines because it gives information about the transient events in a time and frequency plane. The results of CWT analysis are provided and compared with the mean flows of DWT first decomposition level for all cycles at a position. Low frequency high energy found with CWT corresponds well with the peak locations of the mean velocity. The high frequency flows caused by the intake jet gradually decay as the piston approaches the bottom dead center(BDC).

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.1
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• pp.93-99
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• 2011

In this study, a series of laboratory experiments are carried out to analyze fluid behaviors around multi-arranged (2 pieces) floating breakwaters with various parameters such as distance between structures, wave periods and steepness. The rate of wave transmission is shown to be affected directly by wave periods of incident waves and the breakwaters with multi-arranged structures show the highest rate of wave protection compared with other cases. The velocity fields around the breakwaters are measured by using the Laser Doppler Velocimetry system. The transmission coefficients are also measured in laboratory experiments. Finally, laboratory observed data are compared with numerical experimental results and analyzed in detail.

• Journal of Mechanical Science and Technology
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• v.16 no.7
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• pp.986-998
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• 2002

Flow and spray characteristics are critical factors that affect the performance and exhaust emissions of a direct injection diesel engine. It is well known that the swirl control system is one of the useful ways to improve the fuel consumption and emission reduction rate in a diesel engine. However, until now there have only been a few studies on the effect of flow on spray. Because of this, the relationship between the flow pattern in the cylinder and its influence on the behavior of the spray is in need of investigation. First, in-cylinder flow distributions for 4-valve cylinder head of DI (Direct Injection) Diesel engine were investigated under steady-state conditions for different SCV (Swirl Control Valve) opening angles using a steady flow rig and 2-D LDV (Laser Doppler Velocimetry). It was found that swirl flow was more dominant than that of tumble in the experimented engine. In addition, the in-cylinder flow was quantified in terms of swirl/tumble ratio and mean flow coefficient. As the SCV opening angle was increased, high swirl ratios more than 3.0 were obtained in the case of SCV -70° and 90°. Second, spray characteristics of the intermittent injection were investigated by a PDA (Phase Doppler Anemometer) system. A Time Dividing Method (TDM) was used to analyze the microscopic spray characteristics. It was found that the atomization characteristics such as velocity and SMD (Sauter Mean Diameter) of the spray were affected by the in-cylinder swirl ratio. As a result, it was concluded that the swirl ratio improves atomization characteristics uniformly.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.12
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• pp.1111-1118
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• 2010

Combustion measurements based on optical techniques have recently become of major interest as tools not only for clarifying the combustion mechanism but also for validating the computational results for the combustion fields. In this study, the particle behavior in turbulent pulverized coal flame are investigated using advanced optical diagnostics. A laboratory-scale pulverized coal combustion burner is specially fabricated as open type in order to apply various optical measurement techniques. The detailed particle behavior is performed by LDV (laser Doppler velocimetry) and SDPA (shadow Doppler particle analyzer). It is observed that the particle mean diameter increase as the distance from burner increases, and this is found to be caused by the decrease of small particles' diameter and increase of large particles' diameter. This is because of result in the char reaction and the particle swelling due to devolatilization, respectively. The size-classified streamwise velocities of pulverized coal particles in the central region of the jet show the same magnitude, whereas those in the outer region are different depending on the particle size. The results show that the velocity and size-classified diameter of the pulverized coal particles in the flame can be measured well by SDPA.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.6
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• pp.515-521
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• 2017

Large Cavitation Tunnel (LCT) of KRISO enables us to conduct cavitation tests of the propeller attached to a ship model. As the ship model tests are done at rather high Reynolds number of 107~108, flow measurement system such as pitot tube cannot be employed because of structural safety problems in its system and difficulties in installing it within the test section. Thus, KRISO has developed new 3-D LDV system used in large test section of LCT. There are several difficulties in using 3-D LDV, which did not allow efficient operation of it. The first trouble was the calibration using the conventional pin hole. To make the focus with same laser-beam waists at the wanted position, the high spatial resolution CCD is utilized in the calibration procedure for 3-D LDV. The off-axis configuration provides two velocity components in the horizontal plane and on-axis configuration gives third velocity component in the vertical plane. The horizontal velocity components are also obtained in the coincidence mode, which prevents any misleading results in the off-axis configuration. The nominal wake of Aframax tanker model is measured by the developed 3-D LDV system. The measured hull wake showed good agreement with that obtained by CFD calculation.

• Journal of Ocean Engineering and Technology
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• v.11 no.2
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• pp.107-112
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• 1997

본 연구는 자유표면 인삭을 위한 실험 기법 개발에 관한 연구이다. 2차원 수중익에 의해 발생되는 자유표면파를 연구대상으로 삼았다. 실험은 회류수조에서 행하였다. NACA 0012 수중익을 여러가지 길이와 2가지양각에 대해서 실험한 결과 생기는 비선형 자유표면 파를 인식할 수 있도록 영상처리 기술을 도입하였다. 실헙결과 얻은 자유표면 형상을 다른 연구자의 결과와 비교하였다. 비교결과 영상처리의 기법이 자유표면을 인식하는데 대단히 유용한 도구임을 알 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2773-2778
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• 1994

Tumbling motion is very effective for turbulence enhancement during compression process in the cylinder of 4-valve engines. In this paper the tumble decay mechanism for different intake port configuration were measured using laser Doppler velocimetry. Analysis of the tumble decay mechanism was achieved by means of two non-dimensional parameters, defined as tumble eccentricity and shape factor in tumble velocity profile, in addition to the tumble moment.