http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
인접한 두 수중운동체 주위의 유동 해석을 위한 가상경계법의 적용
이경준(K. Lee),양경수(K.S. Yang) 한국전산유체공학회 2013 한국전산유체공학회지 Vol.18 No.1
Analysis of fluid-structure interaction for two nearby underwater vehicles immersed in the sea is quite challenging because simulation of flow around them is very difficult due to the complexity of underwater vehicle shapes. The conventional approach using body-fitted or unstructured grids demands much time in dynamic grid generation, and yields slow convergence of solution. Since an analysis of fluid-structure interaction must be based on accurate simulation results, a more efficient way of simulating flow around underwater vehicles, without sacrificing accuracy, is desirable. An immersed boundary method facilitates implementation of complicated underwater-vehicle shapes on a Cartesian grid system. An LES modeling is also incorporated to resolve turbulent eddies. In this paper, we will demonstrate the effectiveness of the immersed boundary method we adopted, by presenting the simulation results on the flow around a modeled high-speed underwater vehicle interacting with a modeled low-speed one.
원형 실린더가 주기적으로 배열된 채널 유동에 작용하는 유체력
이경준(K. Lee),양경수(K.S. Yang) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.5
Flow-induced forces in the channel flow obstructed by an infinite array of equi-spaced circular cylinders have been numerically studied. An immersed boundary method was employed to facilitate to implement the cylinders on a Cartesian grid system. This flow configuration is relevant to the heat exchangers in which vortex generators play an important role in enhancing the heat-transfer capacity. A parametric study has been carried out to investigate the effects of the gap (G) between the cylinders and the channel wall on flow-induced, forces. The blockage ratio (d/H) and the distance between two neighboring cylinder centers were fixed as 0.2 and 3.33H, respectively, where d and H represent the cylinder diameter and the channel height, respectively. The presence of the circular cylinders arranged periodically in the streamwise direction causes a significant topological change of the flow, leading to a significant change in flow-induced forces and frequency of vortex shedding.
강창우(C.W. Kang),양경수(K.S. Yang) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.5
Direct Numerical Simulation(DNS) of turbulent mass transfer in fully developed turbulent pipe flow has been performed to study the effect of wall boundary conditions on the concentration fields at Re<SUB>r</SUB>=180 based on friction velocity and pipe radius. Fully developed turbulent pipe flows for Sc=0.71 are studied with two different wall boundary conditions, namely, constant mass flux and constant wall concentration. The mean concentration profiles and turbulent mass fluxes obtained from the present DNS are in good agreement with the previous numerical results currently available. To investigate the effects of wall boundary condition on the turbulent mass transfer, the mean concentration profile, root-mean-square of concentration fluctuation, turbulent mass fluxes and higher-order statistics (Skewness and Flatness factor) are compared for the two cases. Furthermore, the budgets of turbulent mass fluxes and concentration variance were computed and analyzed to elucidate the effects of wall boundary conditions on the turbulent mass transfer.
3차원 Floquet 안정성 분석을 위한 가상 경계법의 적용
윤동혁(D.-H. Yoon),양경수(K.-S. Yang) 한국전산유체공학회 2009 한국전산유체공학회지 Vol.14 No.4
An immersed boundary method(IBM, Kim et al.(2001)) for simulating flows over complex geometries is applied to computation of three-dimensional Floquet stability of a periodic wake. Floquet stability analysis is employed to extract different modes of three-dimensional instability. To verify the present method, a fully-resolved Floquet stability calculation for flow past a circular cylinder is considered. There are two different instability modes with long(mode A) and short (mode B) spanwise wavelengths for the periodic wake of a circular cylinder. The critical Reynolds number and the most unstable spanwise wavelengths of modes A and B are computed using the present method, and compared with other authors' results currently available.
강창우(C. Kang),양경수(K.S. Yang) 한국전산유체공학회 2011 한국전산유체공학회지 Vol.16 No.1
Flow instability is investigated in a two-dimensional channel with thin baffles placed symmetrically in the vertical direction and periodically in the streamwise dircetion. At low Reynolds numbers, the flow is steady and symmetric. Above a critical Reynolds number, the steady flow undergoes a Hopf bifurcation leading to unsteady periodic flow. As Reynolds number further increases, we observe the onset of secondary instability. At high Reynolds numbers, the two-dimensional periodic flow becomes three dimmensional. To identify the onset of secondary instability, we carry out Floquet stability analysis. We obseved the transition to 3D flow at a Reynolds number of about 125. Also, we computed dominant spanwise wavenumbers near the critical Reynolds number, and visualized vortical structures associated with the most unstable spanwise wave.
한태헌(T.H. Han),양경수(K.S. Yang),윤동혁(D.H. Yoon),이경준(K. Lee) 한국전산유체공학회 2008 한국전산유체공학회지 Vol.13 No.2
Heat transfer on two identical nearby circular cylinders immersed in the uniform cross flow at Re=120 and Pr=0.7 was numerically studied. We consider all possible types of arrangements of the two circular cylinders in terms of the distance between the two cylinders and the inclination angle with respect to the direction of the main flow. It turns out that significant changes in the characteristics of heat transfer are noticed depending on how the two circular cylinders are positioned, resulting in quantitative changes of heat transfer coefficients on both cylinders. Collecting all the numerical results obtained, we propose a contour diagram for averaged Nusselt number for each of the two cylinders. The perfect geometrical symmetry implied in the flow configuration allows one to use those diagrams to estimate heat transfer rates on two identical circular cylinders arbitrarily positioned in physical space with respect to the main flow direction.
새집증후군 저감대책을 위한 실내 오염물질 확산 해석 코드 개발
전현준(H.J. Jeon),양경수(K.-S. Yang),최춘범(C.-B. Choi) 한국전산유체공학회 2010 한국전산유체공학회 학술대회논문집 Vol.2010 No.5
An efficient code has been developed to predict dispersion of indoor air pollutants. The computing capability of the code has been compared with that of a commercial code in a benchmark test. After that, the code has been employed to compute dispersion of a pollutant released from a new furniture, a kind of Sick Building Syndrome(SBS). A sofa which generates formaldehyde is implemented by using an immersed boundary method. Large Eddy Simulation (LES) is employed to obtain time-dependent velocity and concentration fields. LES has been regarded as an academic tool, but the newly-developed code reveals a possibility of application of LES to practical problems, especially dispersion of indoor pollutants.
원형 실린더가 주기적으로 배열된 채널 유동의 주 유동 불안정성
윤동혁(D.-H. Yoon),양경수(K.-S. Yang),강창우(C. Kang) 한국전산유체공학회 2010 한국전산유체공학회지 Vol.15 No.3
A parametric study has been carried out to elucidate the characteristics of channel flow with a stream wise-periodic array of cylinders. This flow configuration is relevant to heat exchanger applications. The presence of cylinders in channel flow causes the attached wall boundary layer to separate, leading to significant change in flow instabilities. There exist two kinds of instabilities; flow undergoes a primary instability (Hopf bifurcation) at a lower Reynolds number, and the unsteady two-dimensional flow becomes unstable to three-dimensional disturbances at a higher Reynolds number. We report here the dependencies of the prim my instability as well as the flow characteristics of the subsequent unsteady flow, including flow-induced forces and Strouhal number of vortex shedding, on the distance between the cylinder and the channel wall.
윤동혁(D.-H. Yoon),양경수(K.-S. Yang),강창우(C. Kang) 한국전산유체공학회 2010 한국전산유체공학회 학술대회논문집 Vol.2010 No.5
A parametric study has been carried out to elucidate the characteristics of channel flow with a streamwise-periodic array of cylinders. This flow configuration is relevant to heat exchanger applications. The presence of cylinders in channel flow causes the attached wall boundary layer to separate, leading to significant change in flow instabilities. There exist two kinds of instabilities; flow undergoes a primary instability (Hopf bifurcaiton) at a lower Reynolds number, and the unsteady two-dimensional flow becomes unstable to three-dimensional disturbances at a higher Reynolds number. We report here the dependencies of the primary instability as well as the flow characteristics of the subsequent unsteady flow, including flow-induced forces and Strouhal number of vortex shedding, on the distance between the cylinder and the channel wall.