• Proceedings of the Korea Water Resources Association Conference
• /
• 2010.05a
• /
• pp.478-482
• /
• 2010

최근 개발된 표면영상유속계(Surface Image Velocimetry, SIV)는 하천 표면의 영상을 분석하여 유속을 산정하는 매우 실용적이며 간편한 유속측정 방법이다. 그러나, 표면영상유속계는 수표면의 움직임을 계산하여 표면유속을 산정하기 때문에 야간의 경우 획득영상시 수표면의 움직임을 확인할 수 없어 유속측정이 어렵다는 단점이 있었다. 이 때문에 표면영상유속계의 간편성과 유용성에도 불구하고, 주간에만 유속측정이 가능하여 연속적인 하천유량측정을 하기 어려웠다. 과거 수표면에 야광 입자를 흘려보내면서 야간유속측정을 실시하였으나 대하천의 경우 야광 물질의 크기가 작아 영상내에서 식별이 어렵고, 측정시마다 야광 입자를 뿌려주어야 하기 때문에 환경적인 문제가 있다. 이에 본 연구에서는 적외선 카메라를 이용하여 야간에도 영상획득이 가능하도록 시스템을 개선하였다, 야간 영상획득 장비는 최대 가시거리가 200 m까지 가능하고, 주야간 모두 영상획득이 가능하도록 시스템을 구성하였다. 적외선 카메라에서 획득된 동영상은 초당 최대 30장까지 자동 분할이 가능하여 홍수시 고유속을 분석하기에 문제가 없도록 제작하였다. 이와 같이 제작된 야간유속측정 시스템을 이용하여 동일한 유속조건에 대하여 현장에서 주간과 야간 표면유속 측정의 정확도 분석을 수행한 결과 만족스러운 결과를 얻었으며, 향후 실제 하천유량측정에 적용하게 된다면 보다 간편하게 실시간으로 주야간 유량측정이 모두 가능할 것으로 기대된다.

• Journal of the Korean Society of Visualization
• /
• v.6 no.2
• /
• pp.14-19
• /
• 2008

In this paper, the recirculation flow motion and mixing characteristics driven by air bubble flow in a rectangular water tank is studied. The Time-resolved PIV technique is adopted for the quantitative visualization and analysis. 532 nm Diode CW laser is used for illumination and orange fluorescent particle images are acquired by a PCO 10bit high-speed camera. To obtain clean particle images, 545 nm long pass optical filter and an image intensifier are employed and the flow rates of compressed air is changed from 2 l/min to 4 l/min at 0.5 MPa. The recirculation and mixing flow field is further investigated by the POD analysis technique. It is observed that the large scale counterclockwise rotation and main vortex is generated in the upper half depth from the free surface and one quarter width from the sidewall. When the flow rates are increased, the main vortex core is moved to the side and bottom wall direction.

• Journal of the Korean Society of Visualization
• /
• v.6 no.1
• /
• pp.41-46
• /
• 2008

In this paper, the recirculation flow motion and mixing characteristics driven by air bubble stream in a rectangular water tank is studied. The time-resolved PIV technique is adopted for the quantitative visualization and analysis. 488 nm Ar-ion CW laser is used for illumination and orange fluorescent ($\lambda_{ex}=540nm,\;\lambda_{em}=560nm$) particle images are acquired by a PCO 10bit high-speed CCD camera (1280$\times$1024). To obtain clean particle images, 545 nm long pass optical filter and an image intensifier are employed and the flow rates of compressed air is 3 l/min at 0.5 MPa. The recirculation and mixing flow field is further investigated by time-resolved POD analysis technique. It is observed that the large scale recirculation resulting from the interaction between rising bubble stream and side wall is the most dominant flow structure and there are small scale vortex structures moving along with large scale recirculation flow. It is also verified that the sum of 20 modes of velocity field has about 67.4% of total turbulent energy.

• Journal of the Korean Society of Visualization
• /
• v.18 no.1
• /
• pp.50-58
• /
• 2020

This paper presents flow characteristics of a sweeping jet issued by a feedback-free fluidic oscillator. Overall flow characteristics of feedback-free sweeping jet (FFSJ) were analyzed using flow visualization. The feedback-free sweeping jet has a sinusoidal external flow pattern. The oscillating frequency of the FFSJ is three times higher than that of a conventional sweeping jet at the same Reynolds number. Flow structure and turbulence characteristics were investigated using time-resolved particle image velocimetry (TR-PIV). In instantaneous velocity fields, the flow did not stay at ends but changed the direction continuously in contrast to the conventional sweeping jet. Velocity distributions at each plane which were extracted from mean velocity field has Gaussian distribution, which is similar with a circular jet. The sweep angles were constant as 45° at all Reynolds numbers in the high flow rate regime.