• Journal of Advanced Marine Engineering and Technology
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• v.25 no.4
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• pp.846-856
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• 2001

An experimental study has been made to investigate the effect on wake flow and vortex shedding frequency by vortex stabilizer in Karman vortex type air flow sensor. The conditions investigated include 3 types of shapes and 3 types of separation distances of the vortex stabilizer. The phase averaged technique and smoke-wire flow visualization method are used to understand the detail information. The rolling up position of shear layer is fixed by the influence of the vortex stabilizer. Especially, the convex type vortex stabilizer has shown the more stable repeatability and linearity regarding the vortex shedding frequency compared to the other types.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.332-335
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• 2008

The purpose of this study is analysis of flow field where is around of injector of supersonic combustor which is bluff-body stabilized flame and hyper-mixer type of supersonic combustor injector by using hydrogen or hydrocarbon fuel. Various schemes are evaluated to supersonic backward step flow filed with massive separation region in validation step. Compounded scheme of 5th-order TVD-MUSCL, Roe FDS, S-A DES/DDES has a good performance in base and base-bleed flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.5
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• pp.1649-1660
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• 1996

The flow around a circular cylinder was controlled by an acoustic excitation issued from a thin slit along the cylinder axis. The static pressure distributions around the cylinder wall and flow characteristics in the near wake have been measured. Experiments were performed under three cases of Reynolds number, 7.8 * 10$\^$4/, 2.3 * 10$\^$5/ and 3.8 * 10$\^$5/. The effects of excitation frequency, sound pressure level and the location of the slit were examined. Data indicate that the excitation frequency and the slit location are the key parameters for controlling the separated flow. At Re$\_$d/, = 7.8 * 10$\^$4/, the drag is reduced and the lift is generated to upward direction, however, at Re$\_$d/, =2.3 * 10$\^$5/ and 3.8 * 10$\_$5/, the drag is increased and lift is generated to downward direction inversely. It is thought that the lift switching phenomenon is due to the different separation point of upper surface and lower surface on circular cylinder with respect to the flow regime which depends on the Reynolds number. Vortex shedding frequencies are different at upper side and lower side. Time-averaged velocity field shows that mean velocity vector and the points of maximum intensities are inclined to downward direction at Re$\_$d/ = 7.8 * 10$\^$4/, but are inclined to upward direction at Re$\_$d/ = 2.3 * 10$\^$5/.

• 한국해양학회지
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• v.29 no.2
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• pp.83-94
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• 1994

Two-dimensional tidal and tidal residual currents in Chinhae Bay are investigated by field observations, hydraulic and numerical experiments. The results of hydraulic and numerical model experiments roughly coincide with the field measurements. Maximum tidal currents during the spring and neap tides in Kaduk and Kyunnaeryang channel and the central channel of Chinhae Bay are strong as 90 to 110 and 30 to 40 cm/s respectively, and strong tidal residual currents having numerous eddies take place. Maximum tidal currents during the spring and neap tides in the western and northern parts of the bay are weak as below 30 and 10 cm/s respectively, and also tidal residual currents are relatively weak. Tidal residual currents in the northern part of Kajo-do go toward the north, whereas the currents in the southern part move down the bay, and the currents rotating clockwise occur around Bu-do. The surface currents in the bay depend strongly on the wind and river inflow, and such phenomena are more remarkable during he neap tide than the spring tide.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.524-528
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• 2008

도류제 완성 후에 대한 100년 빈도 홍수시의 흐름(유향과 유속)을 기초로 하여 수치모형실험 결과의 일례를 그림에 나타내었다. 초록에는 오염물질 확산 수치모형실험결과를 시간별로 나타내지안했지만, 오염물질 확산에 대한 수치모형실험의 일반적인 결과를 평가하면 아래와 같다. 우선 흐름은 임랑해수욕장 방향으로 형성되고 청정지역인 방향에서는 남측도류제 설치전보다 복잡한 와류가 형성되어 청정지역 방향으로의 흐름은 미약하다. 모델하천의 빈도별 유출량이 증가함에 따라 큰 변화는 없고, 흐름은 모델하천 하구부 전면해역의 외해 방향으로 형성되며 빈도에 따른 흐름방향의 변화는 거의 없다. 보존성 오염물물 확산 계산 결과를 보면 평수시의 오염물질 영향범위는 양안에 도류제가 완성됨으로 인해 확산이 차단되어 도류제 내부의 오염물의 농도가 가중되고 도류제 전면해역으로의 오염물질의 확산범위가 확대됨을 알 수 있다. 모델하천의 빈도별 유출량이 증가함에 따라 오염물질의 농도가 일정하게 유지될 때 초기유출(3시간)에는 도류제 전면해역의 외해 방향으로의 오염물질 확산이 가속화 되며, 확산범위도 점차 확대된다. 오염물질의 농도가 감소하여 모델하천으로 부터의 오염물질 배출이 감소할 경우(15-24시간)는 오염물질 농도가 점차적으로 저감되며 청정지역으로 확산이 지연됨을 알 수 있다.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.922-926
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• 2004

1970년대부터 시작된 산업화와 도시화는 국토 전반에 걸쳐서 개발을 촉진시켰으며, 그 결과로 나타나기 시작한 홍수재해와 용수부족은 보다 많은 저수시설을 요구하게 되었다. 즉, 홍수유출을 저감시키기 위해서 유역의 저류기능을 강화시킬 수 있는 댐 건설은 이수적인 측면에서 안정적인 용수공급을 보장해주는 수단으로 겸용되어 왔으며, 특히 다목적댐이 건설되면서 하도의 첨두홍수유출량을 줄이는데 크게 기여해 왔다. 댐에 의해 홍수가 사실상 사라진 댐 하류에서는 유사이송이 줄어들면서 주수로는 좁아지며, 낮아진다. 홍수가 없어진 주변 홍수터에는 식생이 활착하여 그 폭이 점차 커지고 하상은 높아진다. 과거 댐 건설 전까지 불안정했던 작은 독려 사주에도 홍수가 없어지면서 식생이 뿌리를 내리게 되고 이로 인하여 식생에 의한 난류변화와 와류의 형성으로 주변에 유사의 퇴적이 증가하게 된다. 결과적으로 식생이 활착할 수 있는 면적이 확장되면서 사주는 점차 넓어진다. 특히, 홍수터나 사주의 외딴 관목 식생에 의한 주변 하상의 세굴, 미립토사의 퇴적, 하상재료의 분급효과는 생태 서식 측면에서 귀중한 휴식처나 피난처를 제공하게 된다. 따라서 본 연구에서는 하도의 상류에 댐이 건설되고 난 후에 댐하류의 하도에서 발생하고 있는 식생 메카니즘과 이로 인한 조도증가와 유속저하 및 홍수소통능력의 저감현상을 규명하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.2062-2072
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• 1991

The effect of free stream turbulence on the flow characteristics behind a circular cylinder is investigated in the present experimental study. The various free stream turbulent intensities are generated by different combinations of cylinder locations and grid shapes. Split film sensor with constant temperature anemometer is used to measure the local instantaneous velocity components. Experimental results demonstrate the large scale coherent structures are rapidly distorted and the Strouhal number is decreased with increasing free stream turbulent intensity.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.47-53
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• 2006

The oxidizer-rich preburner is applied to the high efficiency closed cycle rocket propulsion system. This system is generally operated on oxidizer-fuel mixture ratio over than 50. The spray quality and mixing performance are very important for safe combustion of this preburner. This paper presents basic concept and spray characteristic of the preburner injector.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.522-525
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• 2009

DC-shift phenomenon can be observed in Hybrid rocket combustion. This phenomenon makes performance drop which is structure problem or reduce thrust. Understanding of DC-shift phenomenon, the condition of the hybrid rocket combustion stability can be found. In this paper, the condition of Negative DC-shift was found and made by changing oxidizer flow with pre-post chamber. The Negative C-shift phenomenon and characteristic were defined from the experimental study.

• Journal of computational fluids engineering
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• v.9 no.4
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• pp.41-47
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• 2004

The paper presents numerical simulations of laminar vortex-shedding flows past a circular cylinder for Re ≤ 500. The simulations are performed by solving the unsteady 2-D Navier-Stokes equations with a finite volume method using unstructured grid system. The resulting Reynolds number dependence of the Strouhal number and of the drag and lift coefficients is compared with experiments and with previous numerical results, showing good agreement. It is found that, for the truly laminar Reynolds number range the present calculation method described is capable of producing reasonably accurate results for the main practically relevant parameters such as Strouhal number, drag and lift coefficients.