• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.457-462
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• 1997

현재 국내외 대부분 원자력발전소(이하 원전)의 안전주입방식은 저온관 주입방식을 채택하고 있으며, 안전주입시 노심의 온도와 압력분포가 주요 관심 대상이었다. 하지만 향후 개발될 원전의 안전주입방식은 저온관주입이 아닌 안전주입의 신뢰성을 한단계 높인 원자로용기 직접주입방식인 DVI(Direct Vessel Injection)방식을 채택하고 있는 추세인데, 이 경우 관심분야는 원자로용기 dowmcomer지역까지 확대된다. 즉 저온의 안전주입수가 고온 고압의 원자로용기 downcomer지역으로 직접 주입됨으로 인해 이 지역의 유체유동과 혼합상태 및 온도분포가 주요관심 대상이 되며 이는 원자로용기의 PTS(Pressurized Thermal Shock)해석에 연결된다. 본 연구에서는 LOCA 사고시 DVI방식을 적응한 안전주입수 유입에 의한 원자로용기 downcomer지역의 유제유동과 유체혼합상태 및 온도분포를 열유체 해석 code인 FLUENT를 이용하여 해석하였다. 해석결과에 의하면 사고시 DVI에 의해 유입되는 약55℉인 저온 안전주입수는 유입과 동시에 넓은 지역으로 퍼지면서 dowmcomer지역의 고온 원자로냉각재와 적절히 혼합되어 하향유로를 따라 흐르며 PTS의 발생 원인인 국부적 유체비혼합 현상이나 온도 급하강현상은 발생하지 않는 것으로 나타났다.

• Proceeding of EDISON Challenge
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• 2016.11a
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• pp.15-18
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• 2016

본 연구는 조류발전 터빈의 블레이드 형상 최적화 해석 시스템 개발에 대한 사전연구의 일환으로 EDISON CFD의 프로펠러 단독성능 S/W와 SNUFOAM ShipMesh Advanced 자동격자생성기를 이용하여 조류발전 터빈 주위 유동장에 대한 수치해석을 수행하였다. TSR 조건 변화에 따라 수치해석을 수행하고 이에 대한 power, total coefficient를 동일한 조건에서 수행된 실험결과와 비교 검증하여 해석자의 신뢰도를 확인하였다. 또한, 블레이드 전체를 모델링한 full body 해석과 하나의 블레이드만을 모델링한 single body 해석 결과를 비교하여 경제적이면서 정도 높은 터빈 성능해석 프로세스를 제안하였다. 조류발전 터빈의 TSR 조건 변화에 따라 낮은 TSR 조건에서는 국부적 와동발생에 의해 $C_P$가 감소하는 것을 확인하였고 설계 TSR에서 가장 좋은 효율을 보임을 확인하였다. 이를 통해 suction side의 압력 분포, 팁 와동의 강도 등 성능개선을 위한 주요한 설계변수를 식별하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.4
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• pp.437-442
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• 2010

Flow-accelerated corrosion (FAC) leads to thinning of steel pipe walls that are exposed to flowing water or wet steam. From experience, it is seen that FAC damage to piping at fossil and nuclear plants can result in outages that require expensive repairs and can affect plant reliability and safety. CHECWORKS have been utilized in domestic nuclear plants as a predictive tool to assist FAC engineers in planning inspections and evaluating the inspection data so that piping failures caused by FAC can be prevented. However, CHECWORKS may be occasionally ignore local susceptible portions when predicting FAC damage in a group of pipelines after constructing a database for all the secondary side piping in nuclear plants. This paper describes the methodologies that can complement CHECWORKS and the verifications of CHECWORKS prediction results using numerical analysis. FAC susceptible locations determined using CHECWORKS for two pipeline groups of a nuclear plant was compared with determined using the numerical-analysis-based FLUENT.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.9
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• pp.792-798
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• 2007

catalytic combustion is accomplished by the chemical reaction between fuel and oxidizer at the catalyst surface, different from conventional combustion. Therefore, it is important that the fuel and air stream are well mixed and supplied uniformly prior to the combustion region. If the flow is maldistributed, a hot spot may occur that can lead to subsequent catalyst and substrate damage. Therefore, in order to enhance the mixing and flow uniformity, in this study, the perforated plate is used. A numerical simulation is performed to investigate the variation of flow characteristics by changing various parameters. Under each condition, the uniformity of the flow stream at the entrance of the catalyst section is evaluated and compared. The results show that the uniformity can be effectively improved for most of the case by using the well-designed perforated plates.

• Composites Research
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• v.15 no.6
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• pp.1-7
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• 2002

In VARTM process where a sacrificial medium is used to facilitate the resin flow, the velocity of resin varies drastically between the sacrificial medium and the fiber preform. Although the thickness-to-length ratio of a VARTM product is usually small, a 3-D analysis is prerequisite to analyze the lead-lag flow in the two different media. The problem associated with the full 3-D analysis is the CPU time. A full 3-D numerical mesh comprising large number of nodes requires an impractical CPU time on average computer platforms. In this study, a dual-scale analysis technique was developed. The flow analysis for the entire calculation domain was conducted in 2.5-D, and the 3-D analysis was performed for a small area of special concern. In some numerical examples, the local 3-D analysis could discover an eccentric flow pattern as well as the lead-lag flow that will inevitably be neglected in 2.5-D simulations. The global-local analysis technique practiced in this study can be used to analyze the intricate flow of resin through non-uniform media in affordable CPU times.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.9
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• pp.745-751
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• 2012

Hybrid rocket shows interesting characteristics of complicated mixing layers developed by interactions between turbulent oxidizer flow and mass flow from surface due to fuel vaporization. In this study, compressible LES with a ring structure attached at the entrance of the combustor are performed. According to one recent report, adding a ring structure in the middle of the combustor helps increasing regression rate. From the numerical results, it is seen that vortex structures near the wall becomes stronger due to the interaction with surface mass injection, and the local heat flux increases due to the vortices. This phenomenon is obviously related to the generation of dimple structures which are seen in the number of experiments. Also, the ring structure at the entrance induces strong vortex flow which enhances heat transfer to the wall surface and mixing between fuel and oxidizer as well as reaction efficiency.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.6
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• pp.470-479
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• 2009

The local scour in waves can be thought of as very complex synthetic processes which is influenced by geology of bed material, bed flow in the sea and hydraulics condition. The most research until now be targeted at the scour depth and therefore the local scour width in waves has not been investigated as well. The size of wave or bottom velocity at the bed is direct cause of the local scour among lots of the scour effect factors, and the scour depth and width can be estimated through interrelationship analysis with scour area to use the dimensionless parameters including these such as Keulegan-Carpenter number, Ursell number etc. In this paper, to find out closely relation with the dimensionless parameters and scour width, performed an experiment with the variations of pipe diameters, wave heights and wave periods and then analyzed it. As the result, while Reynolds number and period parameter were seen to disperse local scour width largely, Shields number, KC number and Ursell number appeared good interrelationship. Specially, Shields number doesn't much affect the scour depth but has good relation for the scour width.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.973-976
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• 2011

In this paper, the conjugated heat transfer anslysis was performed about an electric heater used in a combustion test equipment of a combustor engine to figure out a physical phenomenon that heater coil was periodically cut during heating test. The result of analysis is that the temperature of coil at coil inlet region was increased locally because the velocity of air was slow in that region. The coil of heater was moved to 25mm downstream so that the structure stability of coil was assured by the decrease of the coil temperature due to increase of an air velocity.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.1
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• pp.10-17
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• 2003

The steady and transient thermal and flow analysis for liquid helium using for the pressurization of liquid rocket propellant tanks have been conducted numerically. The required inner diameter of helium channel that satisfy the design mass flow rate and velocity, through the steady state analyses for various thermal conditions at the wall, is determined and it is found that due to the sign of Joule-Thomson coefficient of helium, the temperature of helium increase monotonically for adiabatic wall condition. The temporal behavior of helium temperature, density, velocity are also investigated under the existence of local heat inflow on the wall.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.1
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• pp.55-63
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• 2012

The turbulent flow characteristics in a coaxial injector were investigated by the nonlinear $k-{\varepsilon}-f_{\mu}$ model of Park et al.[1] and large eddy simulation (LES). In order to analyze the geometric effects on the scalar mixing for nonreacting variable-density flows, several recessed lengths and momentum flux ratios are selected at a constant Reynolds number. The nonlinear $k-{\varepsilon}-f_{\mu}$�� model proposed the meaningful characteristics for various momentum flux ratios and recess lengths. The LES results showed the changes of small-scale structures by the recess. When the inner jet was recessed, the development of turbulent kinetic energy became faster than that of non-recessed case. Also, the mixing characteristics were mainly influenced by the variation of shear rates, but the local mixing was changed by the adoption of recess.