• International Journal of Fluid Machinery and Systems
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• 제9권1호
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• pp.56-56
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• 2016

• Journal of Advanced Marine Engineering and Technology
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• 제37권7호
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• pp.729-736
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• 2013

The turbulent properties in a mixed statistically stationary flow were investigated experimentally by a pseudo stereoscopic PIV. In order to validate the experimental results, the profiles of the turbulent kinetic energy were evaluated with the flow features. A mechanical agitator having 6 blades was installed at the bottom of the mixing tank (D=60cm, H=60cm). The agitator was rotated with 80rpm clockwise and counter-clockwise. For the measurements, three cameras were used and all were synchronized. The images captured by one of the three cameras was used for the measurement of rotational speed, and the images captured by the other two cameras were used to measure three dimensional components of velocity vectors. All vectors captured at the same rotational angle were phase averaged to construct three-dimensional vector fields to reconstruct the spatial distribution of the flow properties. It was seen that the jet scrolling along the tank was the main source of mixing.

• 대한조선학회논문집
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• 제39권3호
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• pp.48-56
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• 2002

KRISO 3600 TEU 컨테이너 모형선의 반류 유동을 PIV 기법을 이용하여 측정하였다. 본 실험은 시험부의 크기가 $1.0^W{\times}1.0^H{\times}4.5^L(m)$인 회류수조에서 수행되었는데, 선박 반류의 종단면과 횡단면에서 속도장을 측정함으로써 반류의 유동특성을 해석하였다. 실험시 횡단면 측정은 반류영역인 Station -0.5767, -1, -3의 3단면에서 수행하였고, 종단면의 경우 배의 중심 평면에서 우현방향으로 Z/(B/2)=0, 0.1, 0.2, 0.4, 0.6의 5단면에서 속도장을 측정하였다. 자유흐름속도는 $U_O=0.6m/s$로 고정하였는데, 수선간 길이 $L_{PP}=1.5m$에 기초한 레이놀즈수는 약 $Re=9{\times}10^5$이다. 각각의 측정 단면에서 순간속도장 400장을 구하고, 이들을 앙상블(ensemble) 평균하여 평균속도장, 난류운동 에너지 및 와도의 공간분포를 구하였다. 반류영역에는 서로 반대방향으로 회전하는 한 쌍의 longitudinal 보오텍스가 존재하며 수선 근처에 반대방향으로 회전하는 2차 와류가 발생하였다. 하류로 나아감에 따라 longitudinal 보오텍스와 2차 와류는 난류확산과 점성소산에 의하여 강도가 약화되지만 반류영역은 점차 확장된다.

• Journal of Advanced Marine Engineering and Technology
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• 제35권7호
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• pp.957-965
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• 2011

The wakes of a cylindrical body have been investigated. The cylindrical body was attached with a thin film. The film is made of silicon with configurations of 50mm(W) ${\times}$ 150mm(L) ${\times}$ 0.3mm(T). The cylinder wakes have been measured with PIV experiments under the conditions with and without the thin film. The diameter of the installed cylinder body is 30mm and the Reynolds numbers are 2730, 6160 and 9750 with the diameter. The measurement system consists of an Ar-ion laser(6W), a high speed camera(1024 ${\times}$ 992 pixel, 500fps) and a host computer. FFT analyses have been carried out using the velocity vectors obtained by PIV measurements at the point X/D=1.52 and Z/D=0.52. For understanding the three-dimensional flow structures, a new Volumetric PTV(particle tracking velocimetry) has been constructed, in which the same four high-resolution cameras have been used. It has been verified that the flexible film suppresses or damps the vortices separated from the cylinder body, which makes the cylinder's wakes stable. With increase of Re numbers the intensity of the dominant frequency of the wakes become smaller.

• 한국수소및신에너지학회논문집
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• 제24권3호
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• pp.264-274
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• 2013

Piping systems play an important role in gas and oil transferring system. In the piping system, there are many elements, such as valves and flow meters. In order to check their normal operating conditions, each signal from each element is displayed on the monitor in the pipe control room. By the way, there are several accidental cases in the piping system even if all signals from the local elements are judged to be normal on the monitor in the control room. Further, opposite cases often happen even the monitor shows abnormal while the local elements work normal. To overcome this abnormal functions, it is not so easy to construct the environment in which sensors detecting the working states of all elements installed in the piping system. In this paper, a new non-contact measurement technique which can calculate the elements' delicate displacements by using a PIV(particle image velocimetry) and diagnose their working states by using a neural network is proposed. The measurement system consists of a host computer, a micro system, a telescope and a high-resolution camera. As a preliminary test, the constructed measurement system was applied to measure delicate vibrations of mobile phones. For practical application, a pneumatic system was measured by the constructed system.

• 대한기계학회논문집B
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• 제37권5호
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• pp.531-538
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• 2013

원심압축기에서 볼류트는 임펠러와 디퓨저를 통해 나온 유동을 모아주는 역할을 한다. 압축기의 운전점에 따라 볼류트 내부 발생하는 와류의 세기나 패턴이 달라진다. 압축기 설부에서는 압축기의 운전점에 따라 재유입 유동의 특성이 변화하고, 이러한 특성은 압축기의 성능 및 탈설계점에서의 특성을 이해하는데 중요한 역할을 한다. 본 연구에서는 PIV를 이용하여 압축기의 운전점에 따라 볼류트 내부에 발생하는 스크롤 와류를 측정하였으며, 압축기 설부 근처에서 유동장을 측정한 결과 유량계수가 감소할수록, 설부 측에 발생하는 박리영역이 줄어들고 압축기로 재유입되는 유동이 커지는 것을 알 수 있다.

• Wind and Structures
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• 제26권6호
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• pp.397-413
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• 2018

Excitation mechanism of interference effect between two tall buildings is investigated with wind tunnel experiments. Synchronized building surface pressure and flow field measurements by particle image velocimetry (PIV) are conducted to explore the relationship between the disturbed wind flow field and the consequent wind load modification for twin buildings in tandem. This reveals evident excitation mechanisms for the fluctuating across-wind loads on the buildings. For small distance (X/D < 3) between two buildings, the disturbed flow pattern of impaired vortex shedding is observed and the fluctuating across-wind load on the downstream building decreases. For larger distance ($X/D{\geq}3$), strong correlation between the across-wind load of the downstream building and the oscillation of the wake of the upstream building is found. By further analysis with conditional sampling and phase-averaged techniques, the coherent flow structures in the building gap are clearly observed and the wake oscillation of the upstream building is confirmed to be the reason of the magnified across-wind force on the downstream building. For efficient PIV measurement, the experiments use a square-section high-rise building model with geometry scale smaller than the usual value. Interference factors for all three components of wind loads on the building models being surrounded by another identical building with various configurations are measured and compared with those from previous studies made at large geometry scale. The results support that for interference effect between buildings with sharp corners, the length scale effect plays a minor role provided that the minimum Reynolds number requirement is met.

• 대한기계학회논문집B
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• 제26권4호
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• pp.578-586
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• 2002

Flow structures around a rectangular prism have been investigated by using a PIV(Particle Image Velocimetry) technique. A thick turbulent boundary layer was generated by using spires arid roughness elements. The boundary layer thickness, displacement thickness and momentum thickness were 650mm, 117.4mm and 78mm, respectively. The ratio between the model height(40mm) and the boundary layer thickness H/$\delta$, was 0.06. The Reynolds number based on the free stream velocity and the height of the model was 7.9$\times$10$^3$. The PIV measurements were performed at three different wall normal planes. Three recirculation regions at forward facing step, top of the roof and backward facing step are clearly seen and show three dimensional features. Dramatic changes of flow patterns are observed in the wake regions in the different spanwise wall normal planes. Instead of reattachment and recirculation zone, rising streamlines are depicted at the normal planes near the side wall due to the interaction with a rising horse shoe vortex. The peak of turbulent kinetic energy occurs at the separation bubble on top of the roof and the magnitude is 2.5 times higher compared with that of the wake region.

• 대한기계학회논문집B
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• 제25권5호
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• pp.713-721
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• 2001

Characteristics of the conical vortices on the roof corner of a rectangular prism have been investigated by using a PIV(Particle Image Velocimetry) technique. The Reynolds number based on the free stream velocity and the height of the model was 5.3$\times$10$^3$. The mean, instantaneous velocity vector fields, vorticity fields, and turbulent kinetic energy distribution were measured for two different angles of attack, 30$^{\circ}$and 45$^{\circ}$. The PIV measurements clearly observed not only the conical main vortex and the secondary vortex but also the tertiary vortex which is firstly reported in this paper. Asymmetric formation of the corner vortex for the case of 30$^{\circ}$angle of attack produces relatively the high magnitude of vorticity and turbulent kinetic energy around the bigger vortex which generates the peak suction pressure on the roof. Fairly symmetric features of the roof vortex are observed in the case of 45$^{\circ}$angle of attack, however, the dynamic characteristics are proved to be asymmetric due to the rectangular shape of the roof.

• 한국추진공학회지
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• 제15권4호
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• pp.26-34
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• 2011

스월러를 가진 천연가스 연료분사기가 장착된 희박 예혼합 연소기에서 화염구조의 일부분인 재순환 영역의 형성이 연소불안정에 미치는 영향에 대하여 실험적으로 연구를 진행하였다. PIV 계측기법으로 연소장에서의 화염의 안정화 그리고 불안정한 영역에서 유동장을 확인해본 결과 스월러에 의한 재순환 영역은 화염의 안정화 및 난류의 강도뿐만 아니라 재순환영역 형성의 크기에 따른 화염 재점화에도 영향을 미쳐 연소불안정 발생의 원인이 되는 열방출 섭동과 매우 밀접한 관계가 있음을 확인하였다.