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[論文] 실린더 내부 유동장에 대한 흡입 밸브의 편심 효과에 관한 수치적 연구
양희천(H.C.Yang),최영기(Y.K.Choi),유홍선(H.S.Ryou),고상근(S.K.Kauh),허선무(S.M.Huh) 한국자동차공학회 1992 오토저널 Vol.14 No.4
Three dimensional numerical calculation carried out to investigate the eccentricity effect of intake valve on the in-cylinder flow fields for the intake stroke and the compression stroke.<br/> During the intake stroke, a corner vortex in the vicinity of the valve exit interacted strongly with a toroidal vortex in the case of axisymmetric valve. But a weak interaction between the corner vortex and the toroidal vortex occurred due to the eccentricity of the valve in the narrow region between valve and cylinder wall in the case of offset valve.<br/> During the compression stroke, it was found that a solid body rotation was maintained in the radial-circumferential plane in the case of axisymmetric valve. But a weak secondary vortex was formed in the radial-circumferential plane in the case of offset valve, because of the interaction between swirl flows and inward flows towards cylinder axis.<br/> The calculated turbulence intensity presented a similar trend with the experiental results but, in spite of using the modified k-ε model, it was found that the qualitative difference between the numerical results and experimental results was large in the region where the velocity gradient is substantial.
직접분사식 엔진의 분무특성에 미치는 스월의 영향 및 입경분포에 대한 수치해석적 연구
양회천(H.C.Yang),유홍선(H.S.Ryou),최영기(Y.K. Choi) 한국자동차공학회 1993 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
A numerical simulation of the spray characteristics in a direct injection engine was performed 10 study the effects of swirl on spray. This study used the finite volume method. the hybrid and Euler implicit scheme and the modified k-ε turbulence model. Also the spray model which considered breakup, collision and coalescence and evaporation of spray droplets was used.<br/> The calculation results of Sauter mean diameter(SMD) and droplet size distribution were compared with<br/> the experimental data(1-2] in a quiescent environment<br/> As the swirl ratio increased the evaporation rate was increased. due to the wide dispersion of spray<br/> droplets and the strong interaction between spray droplets and gas field.<br/>
[論文] 보올형상과 선회비에 따른 디젤기관 실린더내의 유동장 해석
최영진(Y. J. Choi),양희천(H. C. Yang),유홍선(H. S. Ryou),최영기(Y. K. Choi) 한국자동차공학회 1991 오토저널 Vol.13 No.2
There are many factors which influence on the performance of a diesel engine. The piston bowl shape and swirl ratio are important factors to enhance the fuel-air mixing and flame propagation.<br/> In this study, calculations of the flow field in the cylinder of the diesel engine were carried out using the CONCHAS-SPRAY code for different bowl shapes and swirl ratios.<br/> In the case of constant swirl ratio, vortices which affect fuel-air mixing, evaporation and flame propagation are generated more strongly and consistently in the bowl-piston type combustion chamber than in the flat piston type. With this strong squish effect, injected fuel droplets are widely diffused and rapidly evaporated in the bowl-piston type combustion chamber. Especially a strong squish is developed and large and strong vortices are generated in the edge cutted bowl piston chamber.<br/> As the swirl ratio increases, it is found that a large and strong squish and vortices are generated in the combustion chamber and also fuel droplets are diffused into the entire combustion chamber.
3차원 튜브 뱅크 주위의 난류 유동장 및 열전달에 대한 수치 해석적 연구
박상길,김경원,유홍선,최영기,Park, S.K.,Kim, K.W.,Ryou, H.S.,Choi, Y.K. 대한설비공학회 1996 설비공학 논문집 Vol.8 No.3
Turbulent flow and heat transfer characteristics around staggered tube banks were studied using the 3-D Navier-Stokes equations and energy equation governing a steady incompressible flow, which were reformulated in a non-orthogonal coordinate system with cartesian velocity components and discretized by the finite volume method with a non-staggered variable arrangement. The predicted turbulent kinetic energy using RNG $k-{\varepsilon}$ model was lower than that of standard $k-{\varepsilon}$ model but showed same result for mean flow field quantities. The prediction of the skin friction coefficient using RNG $k-{\varepsilon}$ model showed better trend with experimental data than standard $k-{\varepsilon}$ model result. The inclined flow showed higher velocity and skin friction coefficient than transverse flow because of extra strain rate ($\frac{{\partial}w}{{\partial}y}$). Also, this was why the inclined flow showed higher local heat transfer coefficient than the transverse flow.
주 유동의 난류특성이 원통 표면에서의 열전달에 미치는 영향에 관한 연구 - 수치 해석적 고찰 -
박정훈,최영기,유홍선,Park, J.H.,Choi, Y.K.,Ryou, H.S. 대한설비공학회 1991 설비공학 논문집 Vol.3 No.3
Numerical analysis has been performed to investigate the effects of the turbulence intensity and Prandtl number on the local heat transfer around a circular cylinder in crossflow. The governing equations were reformulated in a non-orthogonal coordinate system with Cartesian velocity components and discretised by the finite volume method with a non-staggered variable arrangement. For laminar flow, the calculations were performed for the Reynolds numbers 26 and 200. The results showed good agreement with the experimental results. For turbulent flow of the Reynolds number $1{\times}10^5$ and $2{\times}10^6$, the results showed that with an increase in the turbulent intensity in the main stream, the local Nusselt number increases in the front region of the circular cylinder. But the effect of turbulent intensity on the local Nusselt number diminishes in the wake region. The influence of Prandtl numbers show similar trend to that of turbulent intensity.
알루미늄 복합 외장재를 사용한 고층 건축물의 외기 풍속, 풍향 변화가 화염전파에 미치는 영향에 대한 수치해석 연구
김홍진(H.J. Kim),배승용(S.Y. Bae),최영기(Y.K Choi),유홍선(H.S. Ryou) 한국전산유체공학회 2011 한국전산유체공학회 학술대회논문집 Vol.2011 No.5
The aluminum composite panel are widely used for the external materials of high rise building because of well insulation of heat and sound, and improved Constructability. However, the polyethylene in main material of the aluminum composite panel shows weakness in thermal and fire resistances. For this reason, flame is spread more quickly when the fire break out. Therefore, the potentiality of fire spread to the exterior wall is high due to difficulty of early extinguishment and effect of external air. In this study, numerical investigation was performed by using FDS program for flame spread characteristics with various external air velocity and direction in ten-story building with the aluminum composite external materials. As a result, the flame spread velocity is 0.134㎧ and it takes 224 seconds for flames to spread to the 10th floor without external air velocity. however, the flame spread velocity decreases 40% and it takes 348 seconds for flames to spread to the 10th floor when external air velocity is 2.5 ㎧. and air direction is little effect compared to air velocity.