• Asian Journal of Atmospheric Environment
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• 제2권1호
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• pp.1-13
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• 2008

A numerical simulation method has been developed to predict atmospheric flow and stack gas diffusion using a calculation domain of several km around a stack under complex terrain conditions containing buildings. The turbulence closure technique using a modified k-$\varepsilon$-type model under a non hydrostatic assumption was used for the flow calculation, and some of the calculation grids near the ground were treated as buildings using a terrain-following coordinate system. Stack gas diffusion was predicted using the Lagrangian particle model, that is, the stack gas was represented by the trajectories of released particles. The numerical model was applied separately to the flow and stack gas diffusion around a cubical building and to a two-dimensional ridge in this study, before being applied to an actual terrain containing buildings in our next study. The calculated flow and stack gas diffusion results were compared with those obtained by wind tunnel experiments, and the features of flow and stack gas diffusion, such as the increase in turbulent kinetic energy and the plume spreads of the stack gas behind the building and ridge, were reproduced by both calculations and wind tunnel experiments. Furthermore, the calculated profiles of the mean velocity, turbulent kinetic energy and concentration of the stack gas around the cubical building and the ridge showed good agreement with those of wind tunnel experiments.

• 대한기계학회논문집B
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• 제23권2호
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• pp.175-184
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• 1999

A theoretical study on the turbulent round jet diffusion flame impinging on the wall was carried out to predict the characteristics and structure of Impinging jet flame and heat transfer to the wall. Finite chemistry via Arrhenius equation and eddy dissipation model was adopted as a combustion model, and the Favre averaging and $k-{\varepsilon}$ model were Introduced In the theoretical modeling. The SIMPLE algorithm was applied to the calculation. All the transport properties were considered as the variable depending on the temperature and composition. For the parametric study, the distance from nozzle to impinging wall and Reynolds number at nozzle exit were chosen 88 the major parameters. As the results of the present study, the characteristics of flow fields, the distributions of main variables and each chemical species and the flame shapes were obtained. The heat transfer rate from the flame to the wall and the effective heating area were calculated to investigate the Influences of the major parameters on the heat transfer characteristics.

• 대한기계학회논문집B
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• 제23권10호
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• pp.1327-1339
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• 1999

Characteristics of two-phase flow and heat transfer were numerically investigated in a submerged gas Injection system. Effects of both the gas flow rate and bubble size were investigated. In addition, heat transfer characteristic and effects of heat transfer were investigated when temperature of the injected gas was different from that of the liquid. The Eulerian approach was used for the formulation of both the continuous and the dispersed phases. The turbulence in the liquid phase was modeled by the use of the standard $k-{\varepsilon}$ turbulence model. The interphase friction and heat transfer coefficient were calculated by means of correlations available in the literature. The turbulent dispersion of the phases was modeled by introducing a "dispersion Prandtl number". The plume region and the axial velocities are increased with increases in the gas flow rate and with decreases in the bubble diameter. The turbulent flow field grows stronger with the increases in the gas flow rate and with the decreases in the bubble diameter. In case that the heat transfer between the liquid and the gas is considered, the axial and the radial velocities are decreased in comparison with the case that there is no temperature difference between the liquid and the gas when the temperature of the injected gas is higher than the mean liquid temperature. The results in the present research are of interest in the design and the operation of a wide variety of material and chemical processes.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 2001년도 추계 학술발표회 논문집
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• pp.69-76
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• 2001

The coal gasification process of a slurry feed type, entrained-flow coal gasifier was numerically predicted in this paper. By divding the complicated coal gasification process into several simplified stages suh as slurry evaporation, coal devolitilisation and two-phase reactions coupled with turbulent flow and two-phase heat transfer, a comprehensive numerical model was constructed to simulate the coal gasification process. The k-$\varepsilon$turbulence model was used for the gas phase flow while the Random-trajectory model was applied to describe the behavior of the coal slurry particles. The unreacted-core shrinking model and modified Eddy Break-Up(EBU) model were used to simulate the heterogeneous and homogeneous reactions, respectively. The simulation results obtained the detailed informations about the flow field, temperature inside the gasifier. Meanwhile, the simulation results were compared with the experimental data as function of $O_2$/coal ratio. It illustrated that the calculated carbon conversions agreed with the measured ones and that the measurd quality of the atngas was better than the calculated one when the $O_2$/coal ratio increases. The result was related with the total heat loss through the gasifier and uncertain kinetics for the heterogeneous reactions.

• 대한기계학회논문집B
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• 제27권12호
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• pp.1655-1666
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• 2003

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.

• 설비공학논문집
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• 제12권4호
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• pp.398-403
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• 2000

Numerical analysis was conducted to investigate flow and heat transfer characteristics in louver fin exchanger, which were influenced by louver pitch, fin pitch, louver angle and inlet velocity. Standard $k-\varepsilon$ turbulent modelling was used in this study, and compared with laminar modelling. As a result of this study, Nusselt number became smaller as louver pitch or fin pitch was greater. Drag coefficient became smaller as louver pitch or fin pitch was greater, but it was little affected by inlet velocity.

• Journal of Mechanical Science and Technology
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• 제14권9호
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• pp.1013-1019
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• 2000

A numerical investigation was performed to determine the effect of the Gurney flap on a NACA 23012 airfoil. A Navier-Stokes code, RAMPANT, was used to calculate the flow field about the airfoil. Fully-turbulent results were obtained using the standard ${\kappa}-{\varepsilon}$ two-equation turbulence model. The numerical solutions showed that the Gurney flap increased both lift and drag. These results suggested that the Gurney flap served to increase the effective camber of the airfoil. The Gurney flap provided a significant increase in the lift-to-drag ratio relatively at low angle of attack and for high lift coefficient. It turned out that 0.6% chord size of flap was the best. The numerical results exhibited detailed flow structures at the trailing edge and provided a possible explanation for the increased aerodynamic performance.

• Journal of Advanced Marine Engineering and Technology
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• 제27권2호
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• pp.229-237
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• 2003

The flow and heat transfer characteristics at the surface of two-dimensional protruding heated blocks using confined impingement multiple slot jets were computationally investigated Numerical predictions were made for round-edged nozzles at several nozzle-to-target plate spacings and jet-to-jet distances, with turbulent jet Reynolds numbers ranging from 2000 to 7800. The commercial finite-volume code FLUENT was used to solve the heat transfer characteristics and flow fields using a RNG $\textsc{k}-\varepsilon$ model. The computed heat transfer characteristics at the surface of heated blocks were in good qualitative agreement with previous experimental data The results of heat transfer characteristics on the surface of protruding heated blocks are important considerations in electronics Packaging design.

• 에너지공학
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• 제5권1호
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• pp.50-55
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• 1996

상용 code인 Fluent를 이용하여 도자기의 1차 소성로에 대해 온도장과 속도장을 계산하고 열효율을 산출하였다. 수치해석의 변수로는 배출구 및 도자기의 위치를 변화시켰으며, 수치해석 방법은 검사체적에 기초한 유한차분방법 및 Upwind scheme과 SIMPLEC Algorithm을 사용하였고 난류모델로는 표준 k-$\varepsilon$ 모델을 사용하였다. 계산결과 출구 위치가 전체 소성로내 벡터유동의 양상을 크게 좌우하는 것으로 나타났으며, 전체 온도장에 대해서는 복사의 영향으로 큰 차이를 보이지 않았으나 예열대 상부에 출구가 있는 경우와 비교할 때 예열대 또는 냉각대의 측면에 출구가 있는 경우에 그 영역의 온도가 다소 높게 나타났다. 소성품의 위치는 로내 유동장 및 온도 분포에 크게 영향을 끼치지는 않으나 소성품 내 온도는 그 위치하는 영역의 온도 분포에 크게 영향을 받는 것으로 나타났다. 예열대 상부에 출구가 있는 경우 열효율은 17%로 매우 저조하였고 출구에서의 가스온도는 약 1000 K로 매우 높았다.

• 대한조선학회논문집
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• 제42권6호
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• pp.593-600
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• 2005

The finite volume based multi-block RANS code, WAVIS developed at KRISO, is used to simulate the turbulent flow field around the KRISO container ship (KCS) and the modified KRISO tanker (KVLCC2M). The realizable k-$\varepsilon$ turbulence model with a wall function is employed for the turbulence closure. The free surface flow with and without propeller is mainly investigated for the KCS and the double model flow is concerned for the KVLCC2M which is obliquely towed in still water. The computed results are compared with the experimental data provided by CFD Tokyo Workshop 2005 in terms of wave profiles, hull surface pressure and wake distribution with and without propeller for the HCS and wake distribution and hydrodynamic forces and moments with various drift angles for the KVLCC2M.