• Proceedings of the KSME Conference
• /
• 2000.04b
• /
• pp.290-295
• /
• 2000

An experimental study was carried out in a cavity with upper channel and square heat surface by visualization equipment with Mach-Zehnder interferometer and laser apparatus. The visualization system consists of 2-dimensional sheet light by Argon-Ion Laser with cylindrical lens and flow picture recording system. Instant simultaneous velocity vectors at whole field were measured by 2-D PIV system(CACTUS'2000). Obtained result showed various flow patterns. Severe unsteady flow fluctuation within the cavity are remarkable and sheared mixing layer phenomena are also found at the region where inlet flow is collided with the counter-clockwise rotating main primary vortex. Photographs of Mach-Zehnder are also compared in terms of constant heat flux.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.12 no.8
• /
• pp.755-762
• /
• 2000

Natural convection of air in a horizontal annulus with the inner cylinder cooled by the application of a constant heat flux and the isothermally heated outer cylinder is considered. The bifurcation phenomenon of flow patterns and the heat transfer characteristics are numerically investigated. The zero initial condition induces a unicellular flow in a half annulus. A bicellular flow consisting of two counter-rotating eddies in a half annulus can be obtained above a certain critical Rayleigh number. A transition from the bicellular to the unicellular flow occurs with a decrease in Rayleigh number. Hysteresis phenomena have not been observed. In the regime of dual flows, the overall Nusselt number of the bicellular flow is greater than that of the unicellular flow.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2017.05a
• /
• pp.127-127
• /
• 2017

침수식생이 식재된 개수로에서 식생밀도에 따라 유동 및 난류의 특성이 변화된다. 이러한 특성은 식생에서의 유사, 영양물질, 용존 산소 등에 영향을 미치며 수중 생물의 서식에 변화를 준다. 따라서 침수식생이 식재된 개수로 흐름을 이해하는 것은 중요하게 여겨지고 있으며 많은 선행연구자들에 의해 실험 및 수치모의를 통해 활발히 연구되고 있다. 하지만 대부분의 RANS(Reynolds-Averaged Navier-Stokes)를 기반으로 한 선행연구에서는 침수식생의 흐름 특성을 반영하지 않은 모형을 이용하여 정확한 모의 결과를 도출하지 못 하였다. 이에 정확한 침수식생 흐름을 수치모의하기 위해서는 침수식생 흐름의 특성을 반영한 지배방정식을 이용해야 한다. 본 연구의 목적은 침수식생 흐름의 특성을 RANS 모형 중의 하나인 SA (Spalart-Allmaras) model에 반영하고, 식생밀도에 따른 유동 및 난류량을 실측치와 비교하는 것이다. RANS 방정식을 이용하여 난류모델링을 하였으며, 난류폐합문제를 해결하기 위해서 modified SA model을 이용하였다. 침수식생에서의 흐름을 해석하기 위해 운동량방정식에 식생항력을 추가하였다. 선행연구자의 식생수로 실험을 바탕으로 모형검증을 하였으며, 식생밀도에 따라 평균유속 및 난류구조를 확인하였다.

• Fire Science and Engineering
• /
• v.27 no.6
• /
• pp.64-69
• /
• 2013

The Numerical simulation was performed on the flow field around the two-dimensional rectangular bluff body in order to simulate an engine nacelle fire and to complement the previous experimental results of the bluff body stabilized flames. Fire Dynamic Simulator (FDS) based on the Direct Numerical Simulation (DNS) was employed to clarify the characteristics of reacting flow around bluff body. The overall reaction was considered and the constant for reaction was determined from flame extinction limits of experimental results. The air used atmosphere and the fuel used methane. For both fuel ejection configurations against an oxidizer stream, the flame stability and flame mode were affected mainly by vortex structure near bluff body. In the coflow configuration, air velocity at the flame extinction limit are increased with fuel velocity, which is comparable to the experiment results. Comparing with the isothermal flow field, the reacting flow produces a weak and small recirculation zone, which is result in the reductions of density and momentum due to temperature increase by reaction in the wake zone.

• Journal of Navigation and Port Research
• /
• v.31 no.6
• /
• pp.485-490
• /
• 2007

The purpose in having a control rod on a buoy system is to control the motion of it. The system may be composed entirely of a single circular cylinder and a long mooring anchor cable. A control rod has one 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 the effects of mutual interference. then determine the stability characteristics of the body. In this paper, the study of control-rod-attached buoy's 2-dimensional section was accomplished. model tests and numerical simulations had been carried out with different diameters of control rods. and varying the Reynolds number $Re=5,000{\sim}25,000$ based on the cylinder diameter(D=50mm) to predict the performance of the body and the 2 frame particle tracking method Iud been used to obtain the velocity distribution in the flow field. 50mm circular cylinder Iud been used during the whole experiments and measured results had been compared with each other.

• Journal of Energy Engineering
• /
• v.28 no.1
• /
• pp.65-72
• /
• 2019

The Korean government is aiming to produce 20% of the electricity using renewable energy sources by 2030. Ocean renewable energy sources which are abundant in South Korea can do an important role to achieve the goal. This paper introduces a tidal current energy converter utilizing flow induced vibrations which can efficiently work even in the currents slower than 1.0m/s and suggests optimal designs of the tidal energy converter based on speeds of the tidal currents in seven different coastal regions in South Korea. Moreover, the theoretical annual energy production by the tidal converter is estimated at theses costal areas. The total amount of the annual energy production by the tidal energy converter is predicted as 221.77 TWh which is equivalent to 42.3% of the electric consumption of South Korea in 2013. The result shows that the tidal current energy converter can be an important role to achieve the goal of the Korean government.

• ETRI Journal
• /
• v.9 no.3
• /
• pp.90-95
• /
• 1987

반도체 집적 기술의 개발과 실장 기술의 발전으로 전자장치는 점점 열밀도가 높아지고 있다. 여기서는 PBA가 수직으로 배치된 전자장치를 대상으로, 먼저 자연공냉과 PBA사이에서 발생하는 2차원 유동의 열적 특성을 고려한 후에, 최고 온도 상승률에 대하여 비대칭 열유속에서의 상한값과 대칭 열유속에서의 하한값을 구하는 과정을 기술하였다. 이것은 시스팀 설계 초기 단계에서 온도예측을 하여 시스팀 신뢰도를 향상시키도록 하기 위한 것이다.

• The Journal of Engineering Geology
• /
• v.12 no.3
• /
• pp.257-271
• /
• 2002

The vertical distribution of hydraulic conductivity of 3 boreholes located at Kongju National University was estimated by the ambient flow and the pump-induced flow measurements using a heat-pulse flowmeter. The ambient flow measurements showed that a great amount of groundwater (1~2 m$^3$/day) flowed in the boreholes through the conductive fractures. The analyzed conductivity profiles we similar to those of the packer test performed for the same boreholes. The conductive fractures in which the differential net flow changed greatly could be identified by the BIPS logging. The water-quality logging data showed that quality of groundwater changed abruptly at some depths of the boreholes. This change in water quality can be attributed to the presence of conductive fractures that have resulted in the mixing of groundwater of different quality flowing in different fracture channels. However, compared to the flowmeter test, the water-quality logging showed low capability in identifying locations of conductive fractures.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.2 no.2
• /
• pp.30-37
• /
• 1998

This paper investigates the linear stability of wakes with special emphasis on the effect of chemical reaction. Velocity and density profiles for laminar flows are obtained from analytic profiles as well as from simulation. Wakes have two generalized inflection points and two unstable modes-sinuous and varicose modes. For analytical laminar profiles, sinuous modes are more unstable than varicose modes irrespective of density variation, which shows wakes will be destabilized by sinuous modes. Large velocity difference and density difference lead to more unstable wakes due to large momentum difference. For simulated laminar profiles, chemical reaction with stoichiometric chemistry increases temperature and stabilizes the flow due to increase in compressible reacting wades, flow becomes stable as velocity increases due to viscous dissipation.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.222.1-222.1
• /
• 2016

전북대학교 고온플라즈마응용센터에 구축된 0.4 MW 급 분절형 아크 가열 풍동은 초음속 비행과 우주 비행체의 지구 재진입 조건에서의 유사한 환경 모사가 가능하다. 극한상황에서의 고엔탈피 플라즈마 유동은 내열재료의 삭마 거동 연구와 고온재료의 성능평가에 중요한 역할을 수행 할 수 있다. 이러한 고엔탈피 초음속 플라즈마 유동장의 플라즈마 특성 평가 및 진단은 플라즈마와 내열재료의 상호작용 연구에 중요한 변수를 갖는다. 이를 위해 열유속 탐침, 쐐기 탐침, 고속 카메라 및 광분광기 등의 측정장비를 사용하여 열유속, 초음속 플라즈마의 속도, 플라즈마의 방전특성을 관찰하였다. 본 실험에서 사용된 분절형 아크 토치는 마하 3의 속도 유지하기 위해 토치 내부 압력 4 bar, 반응기 압력 40 mbar를 유지하였다. 토치에 공급되는 Ar(5%)+Air(95%)의 방전기체의 유량은 15 g/s 로 토치에 주입 되었다. 또한, 플라즈마 토치에 가해지는 입력전류는 200A ~ 350A로 10MJ/kg 이상의 엔탈피를 갖는 초음속 플라즈마 유동을 형성하였다.