• Fire Science and Engineering
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• v.21 no.4
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• pp.18-24
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• 2007

The purpose of this study is focussed on the numerical predictions of temperature distribution by radiation heat transfer in atrium fire using the field fire model and the CCRHT-3D code. This code uses standard $k-{\varepsilon}$ turbulent model with SIMPLE algorithm and weighted sum of gray gases model regrouping(WSGGM-RG). The WSGGM-RG calculates radiative properties on the reduced computational loads while reserving the accuracy. The numerical results show that lower temperature distributions on the wall and the top ceiling wall can be obtained by considering radiative heat transfer. The temperature on the top ceiling wall can be an important parameter in predicting the operating condition of the sprinkler head.

• Journal of Institute of Convergence Technology
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• v.12 no.1
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• pp.25-30
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• 2022

도심항공교통은 다수의 전기추진 수직이착륙 항공기가 이착륙 가능한 버티포트가 필요하다. 빌딩풍은 고층건물 주변부에서 발생하는 강풍으로 항공기 이착륙과정에서 항공기의 비행 안전성을 크게 훼손시킬수 있다. 본 연구에서는 항공기 이착륙시 발생할 비행안정성 분석을 위하여 먼저 빌딩풍 주변의 유동특성을 분석하는 연구를 수행하였다. 유동해석은 상용CFD 소프트웨어인 SimericsMP를 사용하였으며, 난류 모델은 k-ε RNG 모델을 사용하였다. 해석방법의 타당성을 검증하기 위하여 CAARC 빌딩모델의 표면 압력 계산결과를 풍동시험 결과와 비교⋅검증하였다. 두 개의 고충빌딩이 있는 상황을 가정한 후, 빌딩풍이 빌딩 주변부의 속도분포 변화에 미치는 영향을 분석하였다. 두 개의 고층 건물 사이의 거리가 증가하는 경우 와들 사이의 상호작용이 감소하는 것을 확인했다. 향후 본 연구를 확장하여 다양한 형상의 고충건물이 밀집해 있는 도심지역에 대한 유동해석 연구를 진행하고자 한다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1294-1303
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• 1993

The fully developed turbulent momentum and heat transfer induced by the square-ribed roughness elements on the inner wall surface in concentric annuli is studied analytically based on a modified turbulence model. The analytical results of the fluid flow is verified by experiment. The resulting momentum and heat transfer are discussed in terms of various parameters, such as the radius ratio, the relative roughness, the roughness density, fluid Reynolds number and for heat transfer, fluid Prandtl number. The study demonstrates that certain artificial roughness elements may be used to enhance heat transfer rates with advantages from the overall efficiency point of view.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.4 s.247
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• pp.320-327
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• 2006

The computations of chemically reacting laminar and turbulent flows are performed using the preconditioned Navier-Stokes solver coupled with turbulent transport and multi-species equations. A low-Reynolds number $k-\varepsilon$ turbulence model proposed by Chien is used. The presence of the turbulent kinetic energy tenn in the momentum equation can materially affect the overall stability of the fluids-turbulence system. Because of this coupling effect, a fully coupled formulation is desirable and this approach is taken in the present study. Choi and Merkle's preconditioning technique is used to overcome the convergence difficulties occurred at low speed flows. The numerical scheme used for the present study is based on the implicit upwind ADI algorithm and is validated through the comparisons of computational and experimental results for laminar methane-air diffusion flame and $ H_2/O_2$ reacting turbulent shear flow. Preconditioning formulation shows better convergence characteristics than that of non-preconditioned system by approximately five times as much.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.3
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• pp.25-32
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• 2001

A passive control method of the interaction between a weak normal shock-wave and a turbulent boundary-layer was simulated using two-dimensional Navier-Stokes computations. The inflow Mach number just upstream of the normal shock wave was 1.33. A porous plate wall having a cavity underneath was used to control the shock-wave/turbulent boundary-layer interaction. The flows through the porous holes and inside the cavity were investigated to get a better understanding of the flow physics involved in this kind of passive control method. The present computations were validated by some recent wind tunnel tests. The results showed that downstream of the rear leg of the $\lambda$-shock wave the main stream inflows into the cavity, but upstream of the rear leg of the $\lambda$-shock wave the flow proceeds from the cavity toward to the main stream. The flow through the porous holes did not choke fur the present shock/boundary layer interaction.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.2
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• pp.132-138
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• 2011

In the present article, we investigate numerically turbulent flow of air through compound rectangular channels. Large eddy simulation(LES) is employed for unsteady turbulence modeling. LES gives better predictions for the axial mean velocity distribution than those of other turbulent models. Strong large-scale quasi-periodic flow oscillations are observed in most of the geometries investigated. Such large-scale flow oscillations in compound rectangular channels are similar to the quasi-periodic flow pulsation through the gaps between fuel rod bundle in nuclear reactor. It exists in any longitudinal connecting gap between two flow channels. The frequency of this flow oscillation is determined by the geometry of the gap. The large scale cross motions through the rectangular compound channels induce significant heat transfer enhancement of the compound channel flow.

• Water for future
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• v.23 no.4
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• pp.445-457
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• 1990

In order to predict the dispersion of a thermal discharge with strong turbulent and buoyant effects, the development of a numerical model using turbulence model and its application are significantly increased. In this study, a 3-dimensional steady-state model for the surface discharge of heated water into quiescent water body is developed. For the model closure of turbulent terms the 4-equation turbulence model is used. For economic numerical simulation, the elliptic governing equations are transformed to the partially parabolic equations. In general, the simulated results by the present model agree well to the experimental results by Pande and Rajaratnam. The model characteristics are presented in comparison with the predicted results of the 2-equation turbulence model by McGuirk and Rodi. Applying the 4-equation turbulence model to the Korea nuclear unit 1 at Kori site, feasibility and efficiency of the present model are validated.

• Nuclear Engineering and Technology
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• v.28 no.1
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• pp.56-71
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• 1996

The local hydrulic characteristics in subchannels of 5$\times$5 nuclear fuel bundles with spacer grids were measured at upstream and downstream of the spacer grid for the investigation of the spacer grid effects on turbulent flow structure by using an LDV(Laser Doppler Velocimeter). The measured parameters are axial velocity and turbulent intensity, skewness factor, and flatness factor. Pressure drops were also measured to evaluate the loss coefficient for the spacer grid and the friction factor for rod bundles. From these data, it was found that the turbulent mixing and forced mixing occur up to $x/D^h=10$ and 20 from the spacer grid, respectively. The turbulence decay behind spacer grid behaves in the similar decay rate as turbulent flow through mesh grids or screens. Mixing factors useful in subchannel analysis code were correlated from the data and show the highest value near spacer grid and then have a stable values.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.386-392
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• 2010

The multiphase simulation of a liquid jet in a lab-scale ramjet combustor with a plain orifice type injector was studied with a commercial CFD tool, a FLUENT program. The objectives of the current study are to analysis the breakup characteristics of a hexane liquid jet in a cross flow and to derive the correlation between flow conditions and drag force coefficients in a test section. From the result of a numerical simulation, we concluded that a DPM and Realizable $k-{\varepsilon}$ model with an enhanced wall treatment were available to simulate the multiphase flow simulation. And the calculated distribution of a hexane vapor concentration was well-matched with experimental results.

• Journal of Energy Engineering
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• v.4 no.1
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• pp.23-30
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• 1995

분류층 가스화기 설계를 위한 일차연구로서 가스화기 종횡비, 주입方法, 선회강도 및 주입속도 등에 따른 비반응 난류장 특성을 수치해석적 방법에 의해 파악하였다. 수치해석은 검사체적에 기초한 Patankar의 유한차분방법을 이용하였으며 압력과 속도의 연계문제는 SIMPLEC 알고리즘을, 레이놀즈 전단력은 K- 난류모델을 사용하였다. 입자궤적 계산은 공기역학적 향력만을 고려하였으며 비선형적인 공기저항력에 의한 난류변동상관모델은 고려치 않았다. 이차공기 주입방법(parallell injection과 nonparallel 3$0^{\circ}C$ imjection)에 따른 수치해석을 수행하여 Ar tracer의 질량분율 및 기타 속도에 대한 實驗資料와 비교하여 만족할 만한 結果를 얻었다. 나아가서 假想的인 가스화기 모델을 대상으로 가스화기의 종횡비, 선회강도, 주입속도 및 주입각 등에 따른 와류 形成 위치 등을 포함한 유동장 특성 및 입도에 따른 궤적분석을 시도하였다.