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횡방향으로 정렬된 2개의 정사각주 후류에서의 3차원 불안정성
최춘범(C.-B. Choi),장용준(Y.-J. Jang),윤동혁(D.-H. Yoon),양경수(K.-S. Yang) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
Three-dimensional linear instability in the flow past two square cylinders in side-by-side arrangements are numerically studied by using a Floquet analysis. The distance between the neighboring faces of the two cylinders (G) is the key parameter which affects the secondary instability under consideration. In this paper, we plan to present the critical Reynolds number for the three-dimensional instability and the corresponding spanwise wave number of the most unstable (or least stable) wave for each G. Our results would shed light on a complete understanding of the onset of three-dimensional instability in the presence of two side-by-side square cylinders.
최춘범(C.-B. Choi),장용준(Y.-J. Jang),양경수(K.-S. Yang) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.5
Floquet stability analysis has been carried out to detect the onset of the secondary instability in the laminar flow past a two-dimensional angulated obstacle. The shape of the obstacles considered here includes a normal flat plate up to square cylinder as the aspect ratio(AR) varies. As AR decreases, mode B and mode QP vanish and mode A2 and mode QP2 emerge. This has not been observed in case of flow past a square cylinder. Mode A2 has an odd RT(Reflection Translation) symmetry, and the dominant spanwise wavelength of mode A2 is much shorter than that of mode A. On the other hand, the dominant spanwise wavelength of mode QP2 is about twice longer than that of mode QP. In a partial range of AR, mode A instability becomes unstable and then stable again as Re increases. This distinctive phenomenon can be seen via a closed curve on the neutral stability diagram. Three dimensional calculations of some selected cases were performed for validation.
최춘범(C.-B. Choi),장용준(Y.-J. Jang),이경준(K. Lee),양경수(K.-S. Yang) 한국전산유체공학회 2011 한국전산유체공학회지 Vol.16 No.4
In this study, Fire Dynamic Simulator (FDS) has been improved with the implementation of marker particles. Convectional FDS is able to implement only two curved geometries, namely, circular cylinders and spheres. The introduction of marker particles made it possible to implement arbitrarily curved objects. Moreover, an algorithm that extracts the marker particle information from a model designed by AutoCAD was developed. With the present implementation, applicability of FDS is greatly enhanced, beneficial to both academia and industry.
수직방향으로 정렬된 정사각주 후류에서의 3차원 불안정성
최춘범(C.-B. Choi),장용준(Y.-J. Jang),윤동혁(D.-H. Yoon),양경수(K.-S. Yang) 한국전산유체공학회 2010 한국전산유체공학회지 Vol.15 No.2
Secondary instability in the flow past two square cylinders in side-by-side arrangements is numerically studied by using a Floquet analysis. The distance between the neighboring faces of the two cylinders (G) is the key parameter which affects the secondary instability under consideration. In this paper, we present the critical Reynolds number for the secondary instability and the corresponding spanwise wave number of the most unstable (or least stable) wave for each G. Our results would shed light on a complete understanding of the onset of secondary instability in the presence of two side-by-side square cylinders.
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.
3차원 Floquet 안정성 분석을 위한 가상 경계법의 적용
윤동혁(D.-H. Yoon),양경수(K.-S. Kang),최춘범(C.-B. Choi) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
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.