• Nuclear Engineering and Technology
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• 제37권6호
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• pp.557-564
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• 2005

Air-water countercurrent flow limitation at perforated plates with four holes was investigated in a vertical tank to see the effects of the plate thickness, the number of hole, and the diameter of the hole on the onset of CCFL. The thickness of plates was 1 cm and 4 cm, with a relatively large hole diameter of 5 cm. The collapsed water level formed on the perforated plate and its distribution in the upper plenum were measured. The gas flow rate in the multi-hole plate is relatively higher than one in the single tube because some of holes in the multi-hole plate provide a flow path fur liquid with less air-liquid resistance than in the single tube. The onset of CCFL occurred at nearly the same air flow rate regardless of the plate thickness. The negligible effect of the plate thickness on CCFL means that the flooding is initiated at the top of the plate rather than at its bottom. It turns out that $j_k$ and $K_k$ better fit the data than $H_k$ when hole diameter is greater than 2.86 cm. In our experimental ranges, the collapsed water levels at the onset of CCFL ranged from 7.5 cm to 10.5 cm. There was no three dimensional distribution of water level before and after the onset of CCFL.

• 한국습지학회지
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• 제16권4호
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• pp.389-402
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• 2014

본 연구에서는 기존에 구축 운영 중인 COSFIM과 FLDWAV간 연계를 통해 다기능보 상 하류 구간 등 하천내 주요 관심구간에 대한 1차원 및 2차원 수리분석을 수행할 수 있는 시스템을 개발하고 낙동강 8개 다기능보를 대상으로 사업 전 후 수리특성 분석을 수행하였다. 각 수치모형은 활용목적에 따라 장 단점을 가지고 있기 때문에 상황에 적합한 모형을 선택적으로 활용할 수 있을 것이며, 기존의 1차원 수리 수문 모형으로 분석할 수 있었던 선 개념 지점 개념의 정보 뿐 아니라 추가적으로 공간 격자 개념의 정보를 제공받을 수 있는 다차원 모의를 수행함으로써 하천에서의 물리적 현상을 적절히 고려한 공간적 수리특성을 반영한 하천관리가 가능할 것이다.

• Nuclear Engineering and Technology
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• 제56권1호
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• pp.19-33
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• 2024

In nuclear thermal-hydraulic system codes, most correlations used for vertical pipes, under downward two-phase flow, have been developed considering small pipes or pool systems. This suggests that there could be uncertainties in applying the correlations to accident scenarios involving large vertical pipes owing to the difference in the characteristics of two-phase flows, or flow conditions, between large and small pipes. In this study, we modified the Multi-dimensional Analysis of Reactor Safety KINS Standard (MARS-KS) code using correlations, such as the drift-flux model and two-phase multiplier, developed in a plant-scale air-inflow experiment conducted for a pipe of diameter 600 mm under downward two-phase flow. The results were then analyzed and compared with those based on previous correlations developed for small pipes and pool conditions. The modified code indicated a good estimation performance in two plant-scale experiments with large pipes. For the siphon-breaking experiment, the maximum errors in water flow for modified and original codes were 2.2% and 30.3%, respectively. For the air-inflow accident experiment, the original code could not predict the trend of frictional pressure gradient in two-phase flow as / increased, while the modified MARS-KS code showed a good estimation performance of the gradient with maximum error of 3.5%.

• 대한기계학회논문집B
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• 제41권9호
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• pp.623-629
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• 2017

다공배플을 가진 마이크로연소기에 레이놀즈응력 난류모형을 이용하여 난류유동 및 혼합특성에 대한 수치해석 연구를 수행하였다. 다공배플은 연소실 내부에 다수의 3차원 와유동을 발생시키는 기하학적 특징을 가지고 있다. 그러한 형상특징 중에서 배플두께를 변화시킬 경우 와유동구조의 다양한 변화가 얻어졌다. 여러 와유동중에서 연료유동으로부터 생성된 와유동은 혼합도 증가에 결정적 역할을 하였다. 연소실 내부의 3차원 와유동구조는 배플두께 변화에 따른 유동의 발달상태에 의존하였다. 특히, 배플두께가 연료유입구 직경보다 작을수록 배플구멍 제트유동의 속도분포는 포물선형태에서 안장모양의 형태로 변하였다. 연소실내부의 재순환영역크기 및 혼합도는 이러한 제트유동구조에 밀접한 상관관계를 가졌다.

• 한국추진공학회지
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• 제24권6호
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• pp.69-77
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• 2020

액체 핀틀 추력기의 성능해석을 위해 준 일차원 다상 반응유동 해석코드를 개발하였다. 해석코드의 주요모델로서 다상 유동장, 액적의 기화, 다상 연소, 액체 막냉각 등의 모델들을 적용하였다. 액적기화 모델은 Abramzon의 기화모델을 적용하였으며 연소 모델은 flamelet 모델을 적용하였다. 막냉각 효과는 Shine의 모델을 적용하였다. 각 모델을 사용하여 산소-질소의 Sod shock 튜브, n-decane 액적기화, 케로신 다상연소, 막냉각 길이를 계산하여 선행 연구자의 결과와 비교 검증하였다.

• Journal of Mechanical Science and Technology
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• 제14권9호
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• pp.1005-1012
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• 2000

Numerical optimization techniques combined with a three-dimensional thin-layer Navier-Stokes solver are presented to find an optimum shape of a stator blade in an axial compressor through calculations of single stage rotor-stator flow. Governing differential equations are discretized using an explicit finite difference method and solved by a multi-stage Runge-Kutta scheme. Baldwin-Lomax model is chosen to describe turbulence. A spatially-varying time-step and an implicit residual smoothing are used to accelerate convergence. A steady mixing approach is used to pass information between stator and rotor blades. For numerical optimization, searching direction is found by the steepest decent and conjugate direction methods, and the golden section method is used to determine optimum moving distance along the searching direction. The object of present optimization is to maximize efficiency. An optimum stacking line is found to design a custom-tailored 3-dimensional blade for maximum efficiency with the other parameters fixed.

• Nuclear Engineering and Technology
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• 제42권3호
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• pp.279-296
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• 2010

For the analysis of transient two-phase flows in nuclear reactor components, a three-dimensional thermal hydraulics code, named CUPID, has been developed. The CUPID code adopts a two-fluid, three-field model for two-phase flows, and the governing equations were solved over unstructured grids, which are very useful for the analysis of flows in complicated geometries. To obtain numerical solutions, the semi-implicit numerical method for the REALP5 code was modified for an application to unstructured grids, and it has been further improved for enhanced accuracy and fast running. For the verification of the CUPID code, a set of conceptual problems and experiments were simulated. This paper presents the flow model, the numerical solution method, and the results of the preliminary assessment.

• 한국지하수토양환경학회지:지하수토양환경
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• 제7권4호
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• pp.10-16
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• 2002

본 연구의 목적은 누수대수층으로 분리된 다층-대수층에 대한 지하수 해석이다. Crank-Nicolson방법에 의한 유한차분법을 적용하여 1차원이며 정상상태인 2중 대수층 구조에 대해 해석해와 비교하였다. 수치해와 해석해는 거의 일치하였으므로 수치해를 2차원의 확장된 다층-대수층 구조에 적용하였다. 이는 한 개 또는 여러 개의 대수층에서 양수하는 경우에 각 대수층에서의 수두값을 계산할 수 있게 하였다. 본 연구는 지하수의 효율적인 운영에 도움이 될 것이다.

• 대한조선학회논문집
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• 제45권1호
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• pp.10-17
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• 2008

In this paper an accurate and stable gridless method that can be applied to multi-dimensional convection problems is developed on a flow directional local grid. A two dimensional pure convection problem is calculated and more accurate and stable solution is obtained compared with other schemes in grid method. The tested numerical schemes include 1st-order upwind scheme, 2nd-order Leith scheme, 3rd-order MUSCL, and QUICK scheme. It is seen that more accurate results are expected when the schemes combined with a MMT control limiter.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.847-852
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• 2000

Three dimensional CFD investigations are carried out to understand the complex flow field in a gas turbine combustor with multi-element fuel injectors. The gas turbine considered here is the GE7FA model which has aye fuel injectors in each combustor can and utilizes lean-premixed combustion to meet nitric oxide emission requirements. Detailed three-dimensional flow characteristics and fuel-air mixture formation process inside the fuel nozzle and gas turbine combustor including five swirl nozzle tips are analyzed using commercial FLUENT code.