축류형 유체기계에서 익단 누설 유동 해석을 위한 난류 모델 성능 평가

이공희,백제현,Lee, Gong-Hee,Baek, Je-Hyun 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.12

It is experimentally well-known that high anisotropies of the turbulent flow field are dominant inside the tip leakage vortex, which is attributable to a substantial proportion of the total loss and constitutes one of the dominant mechanisms of the noise generation. This anisotropic nature of turbulence invalidates the use of the conventional isotropic eddy viscosity turbulence models based on the Boussinesq assumption. In this study, to check whether an anisotropic turbulence model is superior to the isotropic ones or not, the results obtained from the steady-state Reynolds averaged Navier-Stokes simulations based on the RNG k-$\varepsilon$ model and the Reynolds stress model (RSM) are compared with experimental data for two test cases: a linear compressor cascade and a forward-swept axial-flow fan. Through this comparative study of turbulence models, it is clearly shown that the RSM, which can express the production term and body-force term induced by system rotation without introducing any modeling, should be used to predict quantitatively the complex tip leakage flow, especially in the rotating environment.

임의의 종횡비를 가지는 수직축을 중심으로 회전하는 직관과 정지한 고고간 내부의 층류 유동의 유사성에 관한 수치적 연구

이공희,백제현,Lee, Gong-Hee,Baek, Je-Hyun 대한기계학회 2002 大韓機械學會論文集B Vol.26 No.6

The present study showed that a quantitative analogy of the fully developed laminar flows inorthogonally rotating rectangular ducts and stationary curved rectangular ducts of arbitrary aspect ratio could be established. In order to clarify the similarity of the two flows, the dimensionless parameters $K_{LR}$ =Re/√Ro and Rossby number Ro= $w_{m}$/$\Omega$d in a rotating strait duct were used as a set corresponding to Dean number $K_{LC}$ =Re/√λand curvature ratio λ=R/d in a stationary curved duct. Under the condition that the value of Rossby number and curvature ratio was large enough, the flow field satisfied the ‘asymptotic invariance property’: there were strong quantitative similarities between the two flows such as friction factors, flow patterns, and maximum axial velocity magnitudes for the same values of $K_{LR}$ and $K_{LC}$ .

전향 축류형 홴에서의 익단 누설 유동 구조

이공희,명환주,백제현,Lee, Gong-Hee,Myung, Hwan-Joo,Baek, Je-Hyun 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.7

The experiment using three-dimensional laser Dopperr velocimetery (LDV) measurements and the computation using the Reynolds stress model of the commercial code, FLUENT, were conducted to give a clear understanding on the structure of tip leakage flow in a forward-swept axial-flow fan operating at the maximum efficiency condition. The tip leakage vortex was generated near the position of the minimum wall static pressure, which was located at approximately 12% chord downstream from the leading edge of blade suction side, and developed along the centerline of the pressure trough within the blade passages. A reverse flow between the blade tip region and the casing, induced by tip leakage vortex, acted as a blockage on the through-flow. As a result, high momentum flux was observed below the tip leakage vortex. As the tip leakage vortex proceeded to the aft part of the blade passage, the strength of tip leakage vortex decreased due to the strong interaction with the through-flow and casing boundary layer, and the diffusion of tip leakage vortex caused by high turbulence. In comparison with LDV measurement data, the computed results predicted the complex viscous flow patterns inside the tip region, including the locus of tip leakage vortex center, in a reliable level.

회전하는 정사각 단면 U자형 곡관 내부의 유동 발달에 관한 수치적 연구(II) -난류 유동-

이공희,백제현,Lee, Gong-Hee,Baek, Je-Hyun 대한기계학회 2002 大韓機械學會論文集B Vol.26 No.6

The present study investigates in detail the combined effects of the Coriolis force and centrifugal force on the development of turbulent flows in a square-sectioned U-bend rotating about an axis parallel to the center of bend curvature. When a viscous fluid flows through a curved region of U-bend, two types of secondary flow occur. One is caused by the Coriolis force due to the rotation of U-bend and the other by the centrifugal force due to the curvature of U-bend. For positive rotation, where the rotation is in the same direction as that of the main flow, both the Coriolis force and the centrifugal force act radially outwards. Therefore, the flow structure is qualitatively similar to that observed in a stationary curved duct. On the other hand, under negative rotation, where these two forces act in opposite direction, more complex flow fields can be observed depending on the relative magnitudes of the forces. Under the condition that the value of Rossby number and curvature ratio is large, the flow field in a rotating U-bend can be represented by two dimensionless parameters : $K_{TC}$ =Re $\sfrac{1}{4}$√λand a body force ratio F=λ/Ro. Here, $K_{TC}$ has the same dynamical meaning as $K_{TC}$ =Re√λ for laminar flow.

에이스호텔의 건축차별화 전략연구

이공희(Gong-Hee, Lee) 한국생활환경학회 2020 한국생활환경학회지 Vol.27 No.4

This study is focused on the differentiation strategy of ‘Ace Hotel’, ‘community through interaction’, a concept that is not considered by the existing theoretical classification in architectural plan of hotel. The hotel has been built in the same concept and strategy in 11 regions over the past 20 years, showing a high occupancy rate of 80-95%. Through this study, the identification strategy in the architectural plan of the Ace Hotel was identified as 1.The premise of urban regeneration in the site selection, and the possibility of cultural community development as an important factor. 2. Regeneration of peripherality and past time 3. Expansion of shared boundaries. 4. Collaboration through participation of both locals and experts. It is expected that the purpose of this study will be realized by contributing to this differentiation in the planning and planning process of hotel architectural plan in the future.

비상노심냉각계통 주입에 따른 저온관 및 강수관에서 단상 열성층 수치해석

이공희(Gong Hee Lee),정애주(Ae Ju Cheong) 대한설비공학회 2017 설비공학 논문집 Vol.29 No.12

When emergency core cooling system (ECCS) is operated during loss of coolant accident (LOCA) in a pressurized water reactor (PWR), pressurized thermal shock (PTS) phenomenon can occur as cooling water is injected into a cold leg, mixed with hot primary coolant, and then entrained into a reactor vessel. Insufficient flow mixing may cause temperature stratification and steam condensation. In addition, flow vibration may cause thermal stresses in surrounding structures. This will reduce the life of the reactor vessel. Due to the importance of PTS phenomenon, in this study, calculation was performed for Test 1 among six types of OECD/NEA ROSA tests with ANSYS CFX R.17. Predicted results were then compared to measured data. Additionally, because temperature difference between the hot coolant at the inlet of the cold leg and the cold cooling water at the inlet of the ECCS injection line is 200 K or more, buoyancy force due to density difference might have significant effect on thermal-hydraulic characteristics of flow. Therefore, in this study, the necessity to include buoyancy force term in governing equations for accurate prediction of single phase thermal stratification in both cold legs and downcomer by ECCS injection was numerically studied.

한국건축의 콘크리트와 벽전의 신사용법

이공희(Gong-Hee Lee) 한국생활환경학회 2018 한국생활환경학회지 Vol.25 No.2

The study is intended to reveal the contents of the new usage in architectural material(Concrete and Brick), and Korean architecture is currently seeking and to suggest an architectural attempt to reach a new discipline of architecture. Therefore, the study has two kind of objects. One defines new ways of using materials in Korean architecture, and the other is to discover and demonstrate new usage of architectural material. Through the definition and demonstration of this concept, the Korean current architecture classified the three different types of architecture material into the following three different aspects. 1. Change in production process method 2. Modification of field construction method 3. Mix of existing production methods The challenge of this architect is also to make new modules or algorithms of the time from the point of view of building materials and production, and to use the same material gentleman who discovers another value in material properties.

원자로 내부유동 예측을 위한 상용 전산유체역학 소프트웨어 성능 비교 연구

이공희(Gong Hee Lee),방영석(Young Seok Bang),우승웅(Sweng Woong Woo),김도형(Do Hyeong Kim),강민구(Min Ku Kang) 대한기계학회 2013 大韓機械學會論文集B Vol.37 No.12

전산유체역학 소프트웨어의 일부 개발자 및 사용자는 최신 전산유체역학 소프트웨어가 최소한 단상 원자로 안전문제는 타당하게 해석할 수 있을 것으로 생각하지만 계산 결과에는 여전히 제한성 및 불확실도가 존재한다. 현재 한국원자력안전기술원에서는 규제관점에서 원자로 안전문제에 대한 상용 전산유체역학 소프트웨어의 성능평가를 수행하고 있다. 본 연구에서는 축소 APR+ 원자로 내부유동 해석시 다공성 모델을 적용한 상용 전산유체역학 소프트웨어의 예측 성능을 평가하기 위해 ANSYS CFX R.14 및 FLUENT R.14 에 탑재된 수치모델을 이용하여 계산을 수행하였다. 결론적으로 전산유체역학 소프트웨어에 따라 축소 APR+ 원자로 내부유동 분포는 국부적으로 차이가 발생하였다. 비록 제한된 수의 측정치로 인해 상용 전산유체역학 소프트웨어간 예측성능을 평가하기에는 다소 한계가 있으나 CFX R.14 가 FLUENT R.14 에 비해 상대적으로 타당한 예측결과를 제시하였다. 한편 적용된 차분법의 차이로 인해 동일한 격자에 대해 FLUENT R.14 가 CFX R.14 에 비해 상대적으로 많은 계산 메모리를 필요로 하였다. 따라서 대용량 병렬 계산시 가용한 계산 자원에 적합한 전산유체역학 소프트웨어가 선정되어야 한다. Even if some CFD software developers and its users think that a state-of-the-art CFD software can be used to reasonably solve at least single-phase nuclear reactor safety problems, there remain limitations and uncertainties in the calculation result. From a regulatory perspective, the Korea Institute of Nuclear Safety (KINS) is presently conducting the performance assessment of commercial CFD software for nuclear reactor safety problems. In this study, to examine the prediction performance of commercial CFD software with the porous model in the analysis of the scale-down APR (Advanced Power Reactor Plus) internal flow, a simulation was conducted with the on-board numerical models in ANSYS CFX R.14 and FLUENT R.14. It was concluded that depending on the CFD software, the internal flow distribution of the scale-down APR was locally somewhat different. Although there was a limitation in estimating the prediction performance of the commercial CFD software owing to the limited amount of measured data, CFX R.14 showed more reasonable prediction results in comparison with FLUENT R.14. Meanwhile, owing to the difference in discretization methodology, FLUENT R.14 required more computational memory than CFX R.14 for the same grid system. Therefore, the CFD software suitable to the available computational resource should be selected for massively parallel computations.

동일 평면상의 다중 곡관부에 설치된 다공오리피스와 버터플라이밸브 사이의 거리가 밸브의 수력학적 특성에 미치는 영향 평가

이공희(Gong-hee Lee) 한국유체기계학회 2023 한국유체기계학회 학술대회 논문집 Vol.2023 No.12

표면거칠기 및 웨어링 고려가 볼류트 펌프 성능에 미치는 영향에 관한 수치적 연구

이공희(Gong-Hee Lee),이용갑(Yong-Kab Lee),채장범(Jangbom Chai) 대한기계학회 2023 대한기계학회 춘추학술대회 Vol.2023 No.11

As the operation period of the nuclear power plant increases, the surface roughness of the pump may change compared to the time of initial installation due to the various causes(e.g. material erosion, the increased fouling factor). Wearing is installed to allow a small clearance between the impeller and the pump casing for the purpose of preventing wear. In this study, the numerical simulation using ANSYS CFX was performed to find the effect of surface roughness and wearing on the performance of a volute pump. In general, surface roughness plays a role in reducing pump head and efficiency, and increasing pump power. When both wearing and surface roughness were considered, the predicted pump head, power, and efficiency decreased in deviation compared to the measured data.