• Proceeding of EDISON Challenge
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• 2012.04a
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• pp.121-124
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• 2012

비정상 유동 해석을 수행하는데 있어서 비정상 Navier-Stokes 방정식을 적용한 결과와 정상 N-S 지배 방정식을 적용한 결과의 차이를 비교하려한다. 적용하고자 하는 비정상 유동은 대칭형 에어포일 NACA0012 에어포일 주위 유동으로 정하였으며, 이 때 에어포일 시위(chord) 길이와 자유류(free stream) 속도 기준으로 Re=100,000에 해당한다. 계산결과 비정상 지배 방정식을 적용한 경우 비정상 유동박리(flow separation)를 모사 할 수 있었으며, 평균 양력계수($C_L$)와 항력계수($C_D$)는 실험치와 비교적 잘 일치하였다. 하지만 정상 N-S 방정식을 적용했을 경우 비정상 유동을 모사하기 어려웠으며 평균양력, 항력계수도 실험치와 차이를 보였다. 이러한 결과는 비정상 유동 해석시 시간에 따라 변화하는 유동의 특성을 고려해 비정상 N-S 지배 방정식을 적용해야한다는 사실을 보이고 있다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.1
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• pp.61-68
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• 2011

The "ship's routeing" system was adopted by IMO and has been operated on the major sea routes of all over the world for the prevention of marine casualty and the improvement of marine traffic flow. Thereupon, also in Korea, the "Hong-do" and "Bogil-do" sea routes on southern coast were designated to mandatory sea area by traffic separation scheme(TSS) in 2003, and the "Geomun-do" sea route on southern coast was designated in 2005. But there were few or no studies on the effect of designated traffic separation scheme in Korea. For this reason, in this paper, we evaluated the contribution of traffic separation scheme to the prevention of marine casualty and the improvement of marine traffic flow after designation of domestic traffic separation scheme using data of the marine casualties and ship's tracks from AIS information. The results of evaluation showed that on the contrary, the cases of marine casualties were increased on some sea routes and regular traffic flows were disturbed by some vessels after designation of traffic separation scheme. For the safer and better sea routes, alternative ideas such as reposition of ship's routing on "Hong-do" and "Bogil-do" sea areas were suggested.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.1
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• pp.81-89
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• 2017

This study investigates store separation characteristics of an unmanned aerial vehicle having generic stealth configuration over unsteady flow of an internal bay. Free-drop wind tunnel tests are conducted to simulate bomb releases from an internal weapons bay while high-speed camera images are taken. The images are analyzed to examine the effects of flow velocity, angle of attack, flap deflection and the ejector force application on the store separation trajectories. For the free-drop wind tunnel tests, Froude Scaling is applied to match the dynamic similarity for the bomb model, and the ejector force is simulated by using small pneumatic cylinders. The results indicate that the test bomb model safely separates from the internal bay at the given test conditions and configurations. It is also observed that the effects of the flow velocity and ejector force application have greater impacts on the separation trajectories than those of angle of attack and flap deflection.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.285-291
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• 1991

A two-stage slit type virtual impactor based on the concept of the single stage virtual impactor has been designed, fabricated, and evaluated for the purpose of concentrating the suspended particles in the air with the size range of 1.8-4.5 .mu.m and handling large flow volume. Monodisperse methylene blue particles have been generated with vibrating orifice aerosol generator (VOAG). The separation efficiency and concentration efficiency have been measured by the UV-visible absorption spectrometry. Previous study for a single stage virtual impactor were used to determine the design parameters such as 50% cut-off sizes and dimensions of the two stage virtual impactor. The separation efficiency curve and 50% cut-off Stokes number(cut-off sizes) are not sensitive to the nozzle Reynolds number, but sensitive to the ratio between the minor flow rate and the total flow rate, The measured concentration efficiency was compared with the maximum concentration efficiency determined by the separation efficiencies of the first and the second stages. The differences between the measured and the maximum concentration efficiencies result from the wall loss due to the deposited particles on the internal walls inside the impactor.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.4
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• pp.847-864
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• 1988

The main purpose of this study is to investigate the local velocity acceleration in a boundary layer diffusion flame over a flat plate. In order to know the effect of separation on the local velocity acceleration, two typical cases, flows with and without separation, are considered. For these cases, flow visualization using paraffine smoke tracers has been made. Mean velocity and r.m.s. value of fluctuating velocity are measured by using a laser Doppler velocimeter. In addition, measurements of time-mean concentration and time-mean temperature have been made. Time-mean density profiles have been obtained from the data of concentration and temperature. The obtained results are summarized as follows : (1) In the case without separation, the local velocity acceleration is clearly observed near the visible flame zone for all flow conditions. On the while, in the case with serration, the local velocity acceleration is observed only at low free stream velocity and high fuel injection velocity. As increasing the free stream velocity or decreasing the fuel injection velocity, it is not distinctly observed in the mean velocity profile. (2) The r.m.s. value of fluctuating velocity is significantly decreased by combustion in the case with separation. But in the case without separation, the r.m.s. value is increased near the visible flame zone in comparison with cold flow. In both cases, the peak value of r.m.s. appeared just at the visible flame zone, where the mean velocity gradient is not too high.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.9
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• pp.731-737
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• 2014

A vortex chamber is a simple device that separates compressed gas into a high-temperature stream and a low-temperature stream. It is increasing in popularity as a next-generation heat exchanger, but the flow physics associated with it is not yet well understood. In the present study, both experimental and numerical analyses were performed to investigate the temperature separation phenomenon inside the vortex chamber. Static pressures and temperatures were measured using high-sensitivity pressure transducers and thermocouples, respectively. Computational fluid dynamics was applied to simulate 3D unsteady compressible flows. The simulation results showed that the temperature separation is strongly dependent on the diameter of the vortex chamber and the supply pressure at the inlet ports, where the latter is closely related to the viscous work. The previous concept of a pressure gradient wave may not be a reasoning for temperature separation phenomenon inside the vortex chamber.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.5
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• pp.367-375
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• 2017

RANS computational analysis was performed on the head of the launch vehicle including the hammerhead nose pairing in the supersonic regime. The two-dimensional axisymmetric analysis was performed by using laminar, fully turbulent and transition models and compared with the experimental data. It was observed that different flow phenomena occurred depending on the Reynolds number. Under the high Reynolds number condition, the boundary layer becomes turbulent, which is not separated from the surface of the launch vehicle. With the low Reynolds number condition, laminar separation bubble was produced due to the separation and reattachment of the boundary layer on the expansion-compression edge of the hammerhead type nose fairing. The three-dimensional computations with the angle of attack showed a fully detached vortical structure due to the laminar separation bubble. It is proved that the turbulent transition should be considered to predict the separation bubble with the Reynolds number.

• Proceedings of the Membrane Society of Korea Conference
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• 1999.10b
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• pp.117-119
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• 1999

• Proceedings of the Membrane Society of Korea Conference
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• 2002.11a
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• pp.139-141
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• 2002

• Proceedings of the Membrane Society of Korea Conference
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• 2003.11a
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• pp.207-209
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• 2003