• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.5
• /
• pp.708-715
• /
• 1998

The shelter effect of a porous wind fence on a triangular prism was experimentally investigated in a circulating water channel. A porous fence of porosity .epsilon.=38.5% was installed in front of the prism model. The fence and prism model were embedded in a turbulent boundary layer. The instantaneous velocity fields around the fence and prism model were measured by using the instantaneous velocity fields around the fence and prism model were measured by using the 2-frame PTV(Particle Tracking Velocimetry) system. By installing the fence in front of the prism, the recirculation flow region decreases compared with that of no fence case. The porous fence also decreases the mean velocity, turbulent intensity and turbulent kinetic energy around the prism. Especially, at the top of the prism, the turbulent kinetic energy is about half of that without the fence.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.33 no.1
• /
• pp.1-8
• /
• 2009

Recently microscale biofluid flows have been receiving large attention in various research areas. However, most conventional imaging techniques are unsatisfactory due to difficulties encountered in the visualization of microscale biological flows. Recent advances in optics and digital image processing techniques have made it possible to develop several advanced micro-PIV/PTV techniques. They can be used to get quantitative velocity field information of various biofluid flows from visualized images of tracer particles. In this paper, as new advanced micro-PIV techniques suitable for biofluid flow analysis, the basic principle and typical applications of the time-resolved micro-PIV and X-ray micro-PIV methods are explained. As a 3D velocity field measurement technique for measuring microscale flows, holographic micro-PTV method is introduced. These advanced PIV/PTV techniques can be used to reveal the basic physics of various microscale biological flows and will play an important role in visualizing veiled biofluid flow phenomena, for which conventional methods have many difficulties to analyze.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2022.05a
• /
• pp.281-281
• /
• 2022

바닥에서 생성되는 난류는 순간적으로 강한 모멘텀을 바닥에 전달함과 동시에 바닥에 있는 입자를 움직이게 한다. 경계층 내 난류 운동에 대한 분석은 다양한 유사 이송 문제를 이해하기 위해 필수적이며 이에 따라 많은 선행 연구들은 실험실 실험을 통해 해당 연구를 수행하였다. 본 연구에서는 선행 연구에서 사용하지 못했던 진보된 실험 방법을 활용하여 바닥 경계층 내의 난류 운동에 대해 확인하고 해당 운동에 의해 관성 입자의 움직임이 어떻게 발생하는지에 대하여 물리적으로 설명하고자 한다. 다양한 흐름 조건에서 3가지의 입경 크기를 가지는 모래 입자를 가지고 실험을 수행하였으며, 실험 조건별 고해상도 유속장 및 관성 입자의 움직임은 3차원 입자 영상 유속계 (Particle Image Velocimetry; 이하 PIV)와 입자 추적 유속계 (Particle Tracking Velocimetry; 이하 PTV)를 동시에 적용하여 파악하였다. 취득된 3차원 유속장과 입자 궤적을 기반으로 실험 조건별 흐름 및 입자 거동 특성에 대해 분석하였으며, 관성 입자의 움직임을 발생시키는 3차원 난류 운동은 측정된 유속장에서 산정한 Q-criterion 값을 기반으로 도식화하였다. 측정값 내에는 난류 운동에 대한 정보와 더불어 잡음이 포함되어 있으므로 이를 제거하고자 적합 직교 분해 (Proper Orthogonal Decomposition; 이하 POD) 방법을 적용하였다. 그리고 POD로 추출한 유속장을 통해 바닥면 부근에 존재하는 헤어핀 와류 운동 혹은 와류 묶음과 같은 난류 고유 구조를 파악하였다. 해당 와류 운동들의 3차원 난류 특성을 확인하고자 비등방성 불변 지도(anisotropy invariant map)를 활용하였으며 경계층 내부에서 난류의 형태가 흐름 방향으로 늘어진 럭비공 형태임을 확인하였다. 마지막으로, 입자의 움직임을 발생시키는 난류 이벤트를 결정하고자 사방구 분석 (Quadrant analysis) 기법을 적용하였으며 흐름 조건별로 입자를 움직이게 하는 난류 이벤트는 달라짐을 확인하였다.

• The KSFM Journal of Fluid Machinery
• /
• v.9 no.1 s.34
• /
• pp.9-18
• /
• 2006

In the range of very low specific speed ($n_s<0.25$, non-dimensional), the performance of a centrifugal pump is much different from that of a centrifugal pump of normal ns and the efficiency of the pump drops rapidly with the decrease of $n_s$. In order to examine the reason of unstable performance characteristics of the very low $n_s$- centrifugal pump, the internal flow of the pump with a semi-open impeller is measured by a PTV(Particle Tracking Velocimetry) system. The purpose of this study is to make clear the internal flow characteristics and to obtain basic knowledge of the pump performance. The results show that the leakage flow through tip clearance give a strong effect on the flow pattern of impeller passage. A large vortex in the impeller passage and a strong reverse flow at impeller outlet are formed in the range of small flow rates, and the vortex and the reverse flow together reduce the absolute tangential velocity at the impeller outlet and cause the performance instability.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.03b
• /
• pp.689-690
• /
• 2008

In the present study, a micro holographic PTV (HPTV) system was used to experimentally investigate the structure of 3D flow within a curved micro-tube with varying Dean number. The employed HPTV system incorporated a high-speed digital camera to measure the temporal evolution of the 3D velocity fields of micro-scale fluid flows. With increasing Dean number, flow in the curved tube is transformed from a steady flow to a secondary flow with two counter-rotating vortices. In this study, to analyze the 3D flow characteristics in the curved section of tube at a high Dean number, the trajectories of fluid particles were obtained experimentally using the whole 3D velocity field data obtained by the micro HPTV technique. The mean velocity field distribution was then obtained by ensemble averaging the instantaneous velocity fields. These results would be helpful in the design of various passages within micro-scale devices or micro-chips and in understanding the mixing phenomena that occur in curved conduits along the trajectories of fluid particles.

• 한국가시화정보학회:학술대회논문집
• /
• 2006.12a
• /
• pp.1-6
• /
• 2006

Single-Camera Stereoscopic Vision three-dimensional measurement system has been developed based upon 30-PTV algorithm. The system consists of one camera $(1k\times1k)$ and a host computer. To attain three-dimensional measurements a plate having stereo holes has been installed inside of the lens system. Three-dimensional measurements was successfully attained by adopting the conventional 30-PTV camera calibration methods. As applications of the constructed measurement system, a water droplet mixed with alcohol was constructed on a transparent plastic plate with the contacted fluid diameter 4mm, and the particles motions inside of the droplet have been investigated with the constructed measurement system. The measurement uncertainty of the constructed system was 0.04mm, 0.04mm and 0.09mm for X, Y and Z coordinates.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.39 no.7
• /
• pp.549-555
• /
• 2015

A measurement technique of interfacial velocity in air-water separated flow by particle tracking velocimetry using an infrared camera (IR-PTV) was developed. As infrared light with wavelength in the range of 3-5 um could hardly penetrate water, IR-PTV can selectively visualize only the tracer particles existing in depths less than 20 um underneath the air-water interface. To validate the measurement accuracy of the IR-PTV technique, a measurement of the interfacial velocity of the air-water separated flow using Styrofoam particles floating in water was conducted. The interfacial velocity values obtained with the two different measurement techniques showed good agreement with errors less than 5%. It was found from the experimental results obtained using the developed technique that with increasing air velocity, the interfacial velocity proportionally increases, likely because of the increased interfacial stress.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2022.05a
• /
• pp.171-171
• /
• 2022

난류 수체에서 관성입자의 침강속도는 정지 수체에서보다 빠르고, 그 침강속도의 증가비율은 입자의 관성력과 난류의 길이 스케일에 큰 영향을 받는다고 알려져 있다(Wang and Maxey, 1993; Yang and Shy, 2003; Wang et al., 2018). 본 연구에서는 개수로 흐름에서 난류의 영향을 받는 관성입자의 침강속도를 측정하고, 정지 상태의 침강속도에 대한 침강속도의 증가비율과 난류 인자의연관성에 대해 조사하였다. 실험에 사용된 관성입자는 비중 1.35, 직경 300 ㎛에서 2000 ㎛까지의 구형 플라스틱(PE; polyethylene) 입자이며, 해당 입자들의 침강속도는 PTV(particle tracking velocimetry) 방식을 통해 측정하였다. 그리고 PIV(particle image velocimetry) 기법을 통해, 개수로 흐름의 난류 에너지 소산율(energy dissipation rate, ϵ)과 그에 따른 Kolomogorov 길이 스케일을 측정하였다. 실험 결과, 모든 직경 조건에서 플라스틱 입자는 난류 흐름에서의 침강속도가 정지 수체에서의 침강속도보다 빠름을 보였으며, 그 비율은 입자 직경이 난류의 길이 스케일과 유사하거나 작아질 때 큰 폭으로 증가하는 것을 확인하였다. 또한 유체 내에서의 관성입자의 거동에 대한 이론식과 비교하여 관성입자의 침강에 미치는 여러 힘들의 상대적 관계를 파악하였다. 본 연구의 결과는 자연 수체에서 미세플라스틱의 거동을 이해하는데 도움이 될 것으로 기대된다.

• 한국가시화정보학회:학술대회논문집
• /
• 2006.12a
• /
• pp.7-10
• /
• 2006

An experimental study has been conducted to quantitatively characterize the motion of neutrally buoyant particles in 2-dimensional Poiseuille flow through the micron-sized circular capillaries in the range of Re (Reynolds number) $\approx0.1\sim100$. $A{\mu}-PTV$ (Particle Tracking Velocimetry) system is adopted, which consists of a double-headed Nd:YAG laser, an epi-fluorescence microscope and a cooled CCD camera. Since high shear rate can be induced due to the scale effect even at low Re, it is shown that in micro scale neutrally buoyant particles in Poiseuille flow drift away from the wall and away from the center of the capillary. Consequently, particles accumulate at the equilibrium position of $0.52\sim0.64R$ with R being the radius of the capillary, which is analogous to that of tube flow in macro scale. There is a plateau in equilibrium position at small Re, while equilibrium position starts increasing at $Re\approx30$. The outermost edge of particle cluster is closer to the center of the capillary than that in previous studies due to low Re effect. The present study quantitatively presents characteristics of particle motion in circular capillaries. Furthermore, it is expected to give optimum factors for designing microfluidic systems that are to be used fur plasma separation from the blood.

• Proceedings of the KOSOMBE Conference
• /
• v.1993 no.11
• /
• pp.81-84
• /
• 1993

Artificial Heart Valve is the one of the most important artificial organ which has been implanted to many patients. The most important problems related to the artificial heart valve prosthesis are thrombosis and hemolysis. Usual method to test against this problem in vivo experiment, which is complex and hard work. Nowadays the request for In vitro Artificial Heart Valve testing system is increasing. Several papers has announced us flow pattern of Artificial Heart Valve is highly correlated with thrombosis and hemolysis. They usually gel flow pattern by LDA, it is also hard work and has narrow measuring region. In this reason we have determined to develop PTV(Particle Tracking Velocimetry). By using High-speed camera and image processing technique, flow pattern could be relatively easily obtained. Parachute and Bileaflet Artificial Heart Valve designed by SNU were testified.