• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6B
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• pp.641-649
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• 2006

The behavior of a three-dimensional pure rectangular water jet with aspect ratio of 10 was experimentally investigated based on the results of the mean velocity field obtained by PIV. The saddle back distribution was observed in the lateral distribution along the major axis. The theoretical centerline velocity equation derived from the point source concept using the spreading rate for the axisymmetric jet was in good agreement with the measured centerline velocity and gave the division of the potential core region, two-dimensional region, and axisymmetric region. The range of the two-dimensional region divided by the criterion of the theoretical centerline velocity decay for the aspect ratio of 10 was observed to be smaller than that of the transition region. The applicability of the two-dimensional model to the behavior of the rectangular jet with low aspect ratio or the wastewater discharged from a multiport diffuser in the deep water of real ocean may result in significant error in the transition and axisymmetric regions after the two-dimensional region. In the two-dimensional region, the Gaussian constant tended to be conserved, and the spreading rate slightly decreased at the end of the two-dimensional region. The normalized turbulent intensity along the centerline of the jet initially abruptly increased and showed relatively higher intensity for higher Reynolds number.

• Journal of Power System Engineering
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• v.9 no.4
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• pp.31-38
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• 2005

육상 수조식 양식장은 해수를 끌어들여 어류를 기르는 데 사용된다. 본 연구는 사각 수조 내의 다양한 기하학적 관계와 유동에 대한 유동 특성을 도출하였다. 수치해석은 유한 체적법과 SIMPLE 기수법은 수치해석법을 활용하였으며, 비압축성 유체와 3차원 표준 $k-{\varepsilon}$난류 모델을 적용하였다. 속도 분포, 온도 분포에 대한 정보를 확보하였다. 실험과 수치해석의 결과가 정성적으로 잘 일치함을 보였다. 양식장의 깊이가 증가함에 따라 바닥 쪽의 유동이 더욱 안정됨을 확인하였다. 이는 각종 배설물 등의 정체현상으로 연결될 수 있음을 확인하였다. 수조내의 온도는 유입구의 초기 온도가 중요하며, Re 수가 증가할수록 온도는 상승하고 유입구의 반대 벽면 근처의 온도가 유입구 보다 증가함을 알 수 있었다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.6
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• pp.606-613
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• 2007

This study investigates the behavior of a plunging wave and its associated runup and overtopping through velocity measurements and suggests an empirical formula for overtopping velocities on a structure. The plunging wave breaking in front of the structure generates very bubbly flow fields. For measurements of the two phase flow field of the breaking wave, particle image velocimetry and a modified optical method were employed. The obtained velocity fields were discussed in respect of the process of wave impinging, runup and overtopping. The overtopping velocity distribution is found to have a nonlinear profile showing a maximum magnitude at its front part. The relationship of self-similarity among dimensionless parameters is observed and used to obtain the regression formula to depict the overtopping velocity.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.2
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• pp.110-116
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• 2005

This paper deals with interaction between two bubbles or particles and flow around them, visualized by a moving object flow image analyzer(MOFIA) consisting of a three-dimensional (3D) moving object image analyzer(MOIA) and two-dimensional particle image velocimetry(PIV). The experiments were carried out for rising bubbles or particles of various densities, sizes, and/or shapes in stagnant water in a vertical pipe. In the MOFIA employed, 3D-MOIA was used to measure particles or bubbles motion and PIV was used to measure fluid flow, The experimental results showed that the interaction was characterized by the shape, size and density of two particles or bubbles.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.2
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• pp.200-207
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• 2017

The purpose in having a control surface on ships is to control the motion of the ship. The control surface may be composed entirely of a single movable surface or of a combination of fixed and movable portions. A control surface has one sole function to perform in meeting its purpose, and that is to develop a control force in consequence of its orientation and movement relative to the water. The forces and moments generated as a result of this rotation and angle of attack then determine the manoeuvring characteristics of the ship. In this paper, two-dimensional flow characteristics of a flapped rudder and a water-blowing control rudder were accomplished respectively by PIV method in a circulating water channel. Model test has been carried out with different angles of attack of main foil (NACA 0012) and flap's deflection angles to predict the performance of the flapped rudder and the water-blowing control rudder. The 2-frame particle tracking method has been used to obtain the velocity distribution in the flow field. $Re{\fallingdotseq}3.0{\times}10^4$ has been used during the whole experiments and measured results have been compared with each other.

• Journal of Power System Engineering
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• v.20 no.6
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• pp.51-57
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• 2016

Experiment is carried out to investigate the mixed convective flow in three-dimensional horizontal rectangular channels filled with high viscous fluid. The particle image velocimetry(PIV) with thermo-sensitive liquid crystal tracers is used for visualizing and analysis. Quantitative data of temperature and velocity are obtained by applying the color-image processing to a visualized image, and neural network is applied to the color-to-temperature calibration. In this study, the fluid used is silicon oil(Pr=909), the aspect ratio(channel width to heigh) is 4 and Reynolds number is $2{\times}10^{-2}$. From the present study, we can visualize the quantitative temperature and velocity of mixed convective flow in three-dimensional horizontal rectangular channels simultaneously.

• Journal of the Korean Society of Visualization
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• v.4 no.1
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• pp.56-61
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• 2006

A change of three-dimensional vortical structures on the wake behind a road vehicle has been investigated according to the existence of an air spoiler. To reconstruct the three-dimensional velocity fields, two-dimensional PIV(particle image velocimetry) measurements were performed for lots of the x-y, y-z and z-x planes. Since the isovorticity surface does not represent exactly the vortical structures within the recirculation region due to strong shear flows, the velocity component normal to the x-y plane is obtained by interpolating those velocities in the z-x plane. Then, the ${\lambda}_2-definition$ is applied to visualize the vortices in the recirculation region. As a result, it is found that the air spoiler weakens C-pillar vortices and produces strong wing-tip vortices. Inside the recirculation region, the height and volume of coherent vortices are increased relatively when an air spoiler is equipped. On the other hand, two small coherent vortices are observed in case that an air spoiler is absent.

• Journal of the Korean Society for Marine Environment & Energy
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• v.9 no.2
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• pp.79-84
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• 2006

The present study deals with the flow over a flat plate with repeated roughness elements of 2-dimensional rectangular shape, which can be applied into the study on the natural geographical roughness and the turbulent flow on roughened solid surface. Experiment was performed using PIV technique in the circulating water channel. Results showed that the flow over roughness elements was characterized by the high shear flow emanating from top of roughness element and the recirculating region formed at the trough of two roughness elements. In general, the ratio between the spacing and the height of roughness elements plays a crucial role in developing the flow pattern near wall surface.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.11
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• pp.1078-1088
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• 2010

In order to analyze the quantitative characteristics of acoustic streaming, experimental setup of 3-D stereoscopic PIV(particle imaging velocimetry) was designed and quantitative ultrasonic flow fields in the gap between the ultrasonic vibrator and heat source were measured. Utilizing acoustic streaming induced by ultrasonic vibration, surface temperature drop of cooling object was also measured. The study on smart cooling method by acoustic streaming induced by ultrasonic vibration was performed due to the empirical relations of flow pattern, average flow velocity, different gaps, and enhancement on cooling rates in the gap. Average velocity fields and maximum acoustic streaming velocity in the open gap between the stationary cylindrical heat source and ultrasonic vibrator were experimentally measured at no vibration, resonance, and non-resonance. It was clearly observed that the enhancement of cooling rates existed owing to the acoustic air flow in the gap at resonance and non-resonance induced by ultrasonic vibration. The ultrasonic wave propagating into air in the gap creates steady-state secondary eddy called acoustic streaming which enhances heat transfer from the heat source to encompassing air. The intensity of the acoustic streaming induced by ultrasonic vibration experimentally depended upon the gap between the heat source and ultrasonic vibrator. The ultrasonic vibration at resonance caused the increase of the acoustic streaming velocity and convective heat transfer augmentation when the flow fields by 3D stereoscopic PIV and temperature drop of the heat source were measured experimentally. The acoustic streaming velocity of air enhancement on cooling rates in the gap is maximal when the gap agrees with the multiples of half wavelength of the ultrasonic wave, which is specifically 12 mm.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.143-143
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• 2012

최근 우리나라 주요하천에 걸쳐 수행된 '4대강 살리기 사업'에서는 하천에서 발생하는 홍수 및 가뭄재해의 방지를 위한 다양한 사업이 추진되었다. 특히 안정적인 용수공급과 재해방지를 위한 수위확보를 목적으로 4대강 16 개 구간에 걸쳐서 일반적 형태의 고정보와 함께 다양한 형상과 운영방식이 적용된 가동보로 이루어진 다목적보가 설치되었다. 본 연구에서는 4대강 유역(한강, 낙동강, 영산강, 금강)에 설치된 16 개 가동보의 형식 중 4곳(강정고령보, 강천보, 합천창녕보, 창녕함안보)에 적용된 라이징 섹터 게이트(rising sector gate)의 수리학적 특성을 분석하고자 가동보의 수리실험 모형을 개수로에 설치하여 보 주변에서의 흐름 및 난류 특성을 분석하고자 하였다. 4대강 유역에 설치된 라이징 섹터 게이트의 설치목적은 일반적인 고정보의 문제점으로 대두되고 있는 보 상류부의 퇴적토를 신속하게 배사(sediment flushing)하는 데 있다. 이를 위해서는 우선 배사 시에 보 하단부에서 최대유속을 발생시키면서 동시에 최적의 상하류 수위조건을 만족시키는 것이 매우 중요하다. 본 연구에서는 개수로에 설치된 가동보의 수문개방도에 따른 유속분포를 측정하였다. 보 주변에서의 보다 정밀한 유속장의 측정을 위해서 비접촉식 유속측정 방법인 PIV 측정방법을 이용하였다. PIV 측정방법은 일정한 입경과 밀도를 가지며 레이저 반사율이 높은 입자를 흐름에 투입하고 laser 발생장치로 laser sheet를 생성하여 레이저가 반사되어 나타나는 입자 각각의 시간변화에 따른 변위를 CCD 카메라로 가시화한 뒤 유속벡터값을 추출할 수 있게 한다. PIV 측정방법으로 유체의 흐름을 파악하고 시간평균된 유속결과를 바탕으로 난류 특성을 분석하였다. 수로전체 구간에 대하여 3차원 수치해석 프로그램인 FLOW-3D 모의결과와 비교하여 분석하였다. 실험을 통한 유속결과와 수치해석결과는 실험을 통한 유속결과와 비교 분석하였으며, 적용성을 검증한 후 다양한 조건에 대한 설계방안 및 유지관리에 활용하고자 한다.