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유동 방향으로 놓여진 2개의 구를 지나는 유동에 대한 수치 해석적 연구
윤동혁(Dong-Hyeog Yoon),양경수(Kyung-Soo Yang) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
A parametric study on the interactions of two spheres aligned in the streamwise direction is carried out using an immersed boundary method. The numerical results for the case of single sphere for the range of Re ≤ 300 are in good agreement with other authors' experimental and numerical results currently available. Then, our main investigation is focused on identifying the change of the vortical structures in the presence of a nearby sphere aligned in the streamwise direction for the range Re ≤ 220. It turns out that significant changes in physical characteristics are noticed depending on how close the two spheres are. In this paper, not only quantitative changes in the key physical parameters such as the force coefficients, but also qualitative changes in vortex structures are reported and analyzed.
윤동혁(Dong-Hyeog Yoon),양경수(Kyung-Soo Yang) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
In this investigation, flow patterns past two identical nearby spheres at Re=300 were numerically studied. We considered all possible arrangements of the two spheres in terms of the distance between the spheres and, the angle inclined with respect to the main flow direction. It turns out that significant changes in shedding characteristics are noticed depending on how the two spheres are positioned. Collecting all the numerical results obtained, we propose diagrams for flow pattern on the distance vs. angle plane. The perfect geometrical symmetry implied in the flow configuration allows one to use those diagrams to identify flow patterns past two identical spheres arbitrarily positioned in physical space with respect to the main flow direction.
윤동혁(Dong-Hyeog Yoon),양경수(Kyung-Soo Yang) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Large-Eddy Simulation of turbulent flow past a rectangular cylinder confined in channel was carried out to investigate the effects of cylinder aspect ratio on the flow characteristics. It turns out that the key flow statistics such as turbulence intensity, separation point, wall friction and frequency of vortex shedding were significantly affected by the aspect ratio, indicating a possibility of utilizing the large-scale vortices shed from the cylinder to control heat transfer on the channel walls. The present LES results are in good agreement with the experimental results by Nakagawa etal.(1999).
윤동혁(Dong-Hyeog Yoon),양경수(Kyung-Soo Yang),최춘범(Choon-Bum Choi),이경준(Kyongjun Lee) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
A numerical study has been carried out to investigate heat transfer enhancement in channel flow using large-scale vortices. A square cylinder, inclined with respect to the main flow direction, is located at the center of the channel flow, generating a separation region and Karman vortices. Two cases are considered; one with a fixed blockage ratio and the other one with a fixed cylinder size. In both cases, the flow characteristics downstream of the cylinder significantly change depending on the inclination angle. As a result, heat transfer from channel wall is significantly enhanced due to increased vertical-velocity fluctuations induced by the large-scale vortices shed from the cylinder. Quantitative results as well as qualitative physical explanation are presented to justify the effectiveness of the inclined square cylinder as a vortex generator to enhance heat transfer from channel wall.
윤동혁(Dong-Hyeog Yoon),박주엽(Ju Yeop Park),설광원(Kwang-Won Seul) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
Turbulent flow and heat transfer characteristics in helically-coiled tubes have been numerically investigated using ANSYS-CFX 13.0. It has been well known that pressure drop and heat transfer in a helical tube are higher than those in a corresponding straight pipe. However, the detailed characteristics of turbulent flow and heat transfer inside helical tube have not been studied. This paper shows the variation of local Nusselt number and friction factor along the circumference at the wall of a helical tube. CFD simulations are carried out by varying coil diameter and Reynolds number and their influence on turbulent flow and heat transfer also has been studied.
윤동혁(Dong-Hyeog Yoon),양경수(Kyung-Soo Yang) 한국전산유체공학회 2008 한국전산유체공학회지 Vol.13 No.3
In this investigation, flow patterns past two identical nearby spheres at Re=300 were numerically studied. We considered all possible arrangements of the two spheres in terms of the distance between the spheres and, the angle inclined with respect to the main flow direction. It turns out that significant changes in shedding characteristics are noticed depending on how the two spheres are positioned. Collecting all the numerical results obtained, we propose a diagram for flow pattern on the distance vs. angle plane. The perfect geometrical symmetry implied in the flow configuration allows one to use that diagram to identify flow patterns past two identical spheres arbitrarily positioned in physical space with respect to the main flow direction.
윤동혁(Dong-Hyeog Yoon),양경수(Kyung-Soo Yang),최춘범(Choon-Bum Choi),이경준(Kyongjun Lee) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.3
A numerical study has been carried out to investigate heat transfer enhancement in channel flow using large-scale vortices. A square cylinder, inclined with respect to the main flow direction, is located at the center of the channel flow, generating a separation region and Karman vortices. Two cases are considered; one with a fixed blockage ratio and the other one with a fixed cylinder size. In both cases, the flow characteristics downstream of the cylinder significantly change depending on the inclination angle. As a result, heat transfer from channel wall is significantly enhanced due to increased vertical-velocity fluctuations induced by the large-scale vortices shed from the cylinder. Quantitative results as well as qualitative physical explanation are presented to justify the effectiveness of the inclined square cylinder as a vortex generator to enhance heat transfer from channel wall.