• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.226-227
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• 2000

Laser Doppler velocimeters: (LDV)$^{1)}$ 의 대부분의 기본원리는 호모다인(honodyne)방법을 사용한다. 호모다인 방법 중에서 많이 사용되는 방법으로는 마이켈슨 간섭계식과 되먹임식(self-mixing type)$^{2)}$ 이 있다. 마이켈슨 간섭계식은 구성하는데는 많은 광학부품과 정밀한 정렬 장치들을 필요로 한다. 반면에 되먹임식은 레이저 공진기의 고유 주파수와 도플러 이동된 산란광을 공진기 속에서 자체 혼합하여 발생한 차주파수를 레이저 공진기 내부에 있는 pin-photodiode로 측정하므로 마이켈슨 간섭계에 비하여 간단한 장치로 속도계를 구성할 수 있다. (중략)

• Korean Journal of Optics and Photonics
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• v.7 no.2
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• pp.157-161
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• 1996

A simple laser Doppler velocimeter(LDV) using a $CO_2$ laser with its self-mixing effect has been developed. We measured the laser power which was modulated by Doppler frequency, when monochromatic laser light was focused to a moving target. The Doppler-shifted frequency was controlled by changing rotating speed of the turntable or the cosine of the angle between the direction of the laser beam and that of the rotating velocity.

• Journal of the KSME
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• v.34 no.4
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• pp.262-276
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• 1994

본 연구를 통하여 3차원 LDV 시스템의 측정기법을 개발하였으며, 측정결과의 신뢰성을 확인하 였다. 또한 이것을 타원제트 연구에 적용함으로써 그 응용 가능성을 확인하였다. 앞으로 3-D LDV 시스템을 사용하여 신뢰성 있는 측정결과를 얻기 위해서는 아래에 기술한 몇 가지 사항을 고려하여야 한다. 1) 3차원 레이저 유속계는 정교하고 복잡한 광학시스템으로 정확한 배열을 요구한다. 광학계와 실험장치의 좌표축이 일치하지 않으면 축방향보다 측방향(lateral) 속도변동 성분에 큰 영향을 준 다. 2) LDV 측정에서 속도편심을 줄이기 위해서는 적당한 출력의 레이저, 적절한 신호처리(signal conditioning), 실험조건에 알맞는 입자를 선정하여야 한다 3) 입자를 연속적으로 균일하게 공급하여야하며 신호분석기 조작에 익숙하여 도플러신호의 질을 최적화하여야 한다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1774-1780
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• 1991

본 연구에서는 유한 길이를 갖는 수직 덕트내 공기 유동의 속도 분포를 LDV를 사용하여 측정하며 유동 특성에 미치는 가열정도, 덕트간격 및 입구소도등의 영향을 보고하고자 한다. 또한 속도분포, 온도분포 및 열전달에 미치는 부력의 영향을 수치 적으로 예측하여 그 타당성을 검증하고자 한다.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.4
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• pp.494-501
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• 2000

A study on performance of a propeller fan according to the distance between the front plate and the fan was conducted experimentally. Different characteristics of performance were found on the performance curve. Flow measurements using the three dimensional LDV system show that the zone of recirculation exists around the fan. The differences of performance in changes of the distance occurs because the zone of recirculation is much wider at the distance of 24mm than at that of 30mm.

• Korean Journal of Optics and Photonics
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• v.11 no.5
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• pp.306-311
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• 2000

This paper deals with the development of Laser Doppler Vibrometer (LDV) that can mea~ure the tlequency and amphlude of the ultrasonic vibralion. Hc-Ne laser (632.8 om) is used as a light source, and Michelson interferometer in winch frequency of the objective beam is shIfted by Bragg cell IS adopted The frequency modulated signal centered at 40 MHz flom the PIN diode IS amplified. down-col1vel1ed to 2.5 MHz, filtered and digiLized. The voltage output that is proportional to the velocity of the vibratwg surface is obtawed using digItal PLL. A microprocessor is used to extract the frequcncy aud amplitude of the vibratIOn from the voltage output. It is found that the developed LDV can measure up to 300 kHz vibratIOn and the mlillmUITI measurable amplitude is I nm at 300 kHz. We believe thatlhis LDV can be used to measure the vibratIOn of the heavy electric maclllnery and micro-size structures. tures.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.28A no.5
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• pp.361-369
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• 1991

The optics and the signal processor of dual beam laser Doppler velocimeter(LDV) was fabricated. By using the dual beam and the forward scattering, the optics part of LDV was fabricated. And the signal processor of LDV was designed by the frequency counter type using new 11:6 period timing device in order to remove error signals, and was made of the reference clock of a 500 MHz ECL oscillator. Doppler frequencies from 10KHz to 70MHz can be measured using the signal processor. In the accuracy of the period counting part, from 1.81x10**-4% to 1.27% is estimated, and in the accuracy of the validation logic part, from 0.78% to 14.78% is estimated.

• Journal of the Korean Society of Mechanical Technology
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• v.20 no.6
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• pp.757-762
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• 2018

LDV(laser Doppler velocimetry) measurements were conducted on the exit region of the impeller passage and the gap between the impeller and turbine blades under 0.8 speed ratio. The 0.8 speed ratio has an impeller speed of 2000rpm and a turbine speed of 1600rpm. A periodic variation of the mass flow rate is present in many of the measurements made. The frequency of this variation is the same as the frequency of the turbine blades passing the impeller passage exit. It is found that the instantaneous position of the turbine had effect on fluid flow inside the impeller passage and gap region. This study would aid in the construction of higher accuracy CFD models of this complex turbomachinery device.

• 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.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.720-726
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• 2001

Two-dimensional, angle-resolved LDV(Laser Doppler Velocimetry) measurements of the turbulent rotating flow field in a confined cylinder have been performed. The configurations of interest are flows between a rotating upper disk with a rod attached by a disk or impeller(${\theta}= 90^{\circ},\;45^{\circ}$) and a stationary lower disk in a confined cylinder. The mean flow velocity as well as the turbulent intensity of the flow field have been measured. The results show that the flow is strongly dependent on the position of the impellers or the disk, negligibly affected by the Reynolds number in turbulent flow. It is observed that the mixing effect of the axial flow impeller(${\theta}= 45^{\circ}$) is better than that of the radial flow impeller(${\theta}= 90^{\circ}$) or a disk.