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NACA16-020 익형의 단면을 갖는 날개 끝 와류 현상에 대한 3 차원 난류유동 해석
정남균(Namgyun Jeong) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.8
The three-dimensional turbulent wingtip vortex flows have been examined in the present study by using the commercial code FLUENT. The standard k-ε model is used as a closure relationship. The wing is constructed by using an elliptic body whose aspect ratio is 3.8 and the NACA 16-020 airfoil section. The simulations for various angle attack (α=0°, 5°,and 10°) are carried out. The effect of Reynolds number is also investigated in this study. As the angle attack increases, the wingtip vortex becomes stronger. However, the relative vortex strength to inlet velocity decreases as Reynolds number increases.
정남균(Namgyun Jeong) 대한기계학회 2017 大韓機械學會論文集B Vol.41 No.9
최근 기기들이 소형화 되고 이에 따른 효율적인 열방출 방안이 필요해지면서, 마이크로채널에서의 비등에 관한 연구가 주목받고 있다. 그러나 마이크로채널의 경우는 마찰계수 및 열전달 특성이 매크로스케일의 경우와 달라 기존에 매크로스케일에서 도출된 상관식과 비교 시에 큰 오차를 발생시킨다. 또한, 채널 내에서의 비등현상은 메커니즘의 복잡함으로 인하여 실제 문제 적용에 있어서 실험적, 이론적인 방법만으로 접근하는데 무리가 있다. 따라서 이러한 방법들과 더불어 수치해석적인 연구방법이 보완되어져야 하는데, 그동안 수행되어진 연구들은 매크로채널에서의 연구가 대부분이다. 본 연구는 최근 CFD 방법의 대안으로 제시된 격자 볼츠만 방법을 마이크로채널에서의 비등현상을 모의하는데 적용해보았으며, 마이크로채널 내에서의 기포 성장과정에 대하여 예측해 보았다. Recently, efficient heat dissipation has become necessary because of the miniaturization of devices, and research on boiling on micro-channels has attracted attention. However, in the case of micro-channels, the friction coefficient and heat transfer characteristics are different from those in macro-channels. This leads to large errors in the micro scale results, when compared to correlations derived from the macro scale. In addition, due to the complexity of the mechanism, the boiling phenomenon in micro-channels cannot be approached only by experimental and theoretical methods. Therefore, numerical methods should be utilized as well, to supplement these methods. However, most numerical studies have been conducted on macro-channels. In this study, we applied the lattice Boltzmann method, proposed as an alternative numerical tool to simulate the boiling phenomenon in the micro-channel, and predicted the bubble growth process in the channel.
동위원소 생산공정에서 발생한 방사성 폐기물 장기저장소 온도평가
정남균(Namgyun Jeong),조대성(Daeseong Jo) 대한기계학회 2016 大韓機械學會論文集B Vol.40 No.7
본 연구는 의료용 동위원소 생산공정에서 발생하는 방사성폐기물을 저장하는 장기저장소의 온도를 두 가지 방법으로 평가한 결과를 보여준다. 방사성폐기물에서 발생하는 열을 Volume source와 Point source로 가정하여 장기저장소의 온도를 평가한 결과, 폐기물 저장위치에 따른 최대온도분포는 유사하게 나타났으나 그 크기에 있어서 최대 5℃ 정도의 차이를 보였다. 따라서, 개념설계를 위해서는 해석 시간이 오래 걸리는 Volume source를 이용한 3차원 해석보다는 Point source를 이용한 2차원 해석이 보다 효율적이지만, 상세 설계를 위한 정확한 해석 결과를 얻기 위해서는 Volume source를 이용한 3차원 해석이 수반되어야 함을 알 수 있다. In the present study, temperature evaluations on long-term storage of radioactive waste produced in the process of isotope production were performed using two different methods. Three-dimensional analysis was carried out assuming a volumetric heat source, while two-dimensional studies were performed assuming a point source. The maximum temperature difference between the predictions of the volumetric and point source models was approximately 5℃. For the conceptual design level, a point source model may be suitable to obtain the overall temperature characteristics of different loading locations. For more detailed analysis, the model with the volumetric source may be applicable to optimize the loading pattern in order to obtain minimum temperatures.
정남균(Namgyun Jeong) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
For numerical analysis of multiphase flow, each interface boundary should be captured, and the geometric deformation of the interface needs to be predicted. In a way to predict the interface, the singular interface model and diffusion interface model are used. Among them, the lattice Boltzmann method has adopted the diffusion interface model, which is easy to simulate complex multiphase flow phenomena such as bubble collapse, droplet collision, and moving contact lines. In this paper, a lattice Boltzmann method for the simulation of multiphase flows is described, and some test results for the validation are presented.
Horn-type Rudder 주위의 2 차원 난류유동 해석
정남균(Namgyun Jeong) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.11
The two-dimensional turbulent flow around the horn-type rudder has been examined in the present study by using the commercial code FLUENT. The standard k-ε model is used as a closure relationship. The geometry of horn rudder is based on the NACA 0020 airfoil. The simulations for various angle attack (α) and yaw angle(δ) are carried out. The effect of Reynolds number is also investigated in this study. The cavitation is more possible when the yaw angle is 6° and it is more serious as Reynolds number increases.
CURVED BOUNDARY TREATMENT OF THE LATTICE BOLTZMANN METHOD FOR SLIP FLOW SIMULATIONS
Namgyun Jeong(정남균) 한국전산유체공학회 2014 한국전산유체공학회지 Vol.19 No.3
The lattice Boltzmann (LB) method has been used to simulate rarefied gas flows in a micro-system as an alternative tool. However, previous results were mainly focused on a simple geometry with flat walls because the LB method is modeled on uniform Cartesian lattices. When previous boundary conditions for the microflows are applied to curved walls, the use of them requires approximation of the curved boundary by a series of stair steps, and introduces additional errors. For macroflows, no-slip curved wall boundary treatments have been developed remarkably in order to overcome these limits. However, the investigations for the slip curved wall boundary have rarely been performed for microflows. In this work, a curved boundary treatment of the LB method for a slip flow has been introduced. The results of the LB method for 2D microchannel and 3D microtube flows are in excellent agreement with the analytical solutions.