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회전하는 원형 실린더 주위의 층류 유동장에 관한 수치적 연구
이용석(Yong-Suk Lee),윤현식(Hyun-Sik Yoon),두정훈(Jeong-Hoon Doo),하만영(Man-Yeong Ha) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.11
The present study numerically investigates three-dimensional laminar flow past a rotating circular cylinder placed in a uniform stream. For the purpose of a careful analysis of the modification of flow by the effect of the rotation on the flow, numerical simulations are performed at a various range of rotational coefficients (0≤α≤2.5) at one Reynolds number of 300. As α increases, flow becomes stabilized and finally a steady state beyond the critical rotational coefficient. The 3D (three dimensional) wake mode of the stationary cylinder defined at this Reynolds number has been disorganized according to α, which were observed by the visualization of 3D vortical structures. The variation of the Strouhal number is very weak when the wake pattern is changed according to the rotational coefficient. As α increases, the lift increases, whereas the drag decreases.
종횡비에 따른 자유 회전하는 사각 실린더 주위의 유동장에 관한 수치적 연구
박용갑(Yong-Gap Park),윤현식(Hyun-Sik Yoon),하만영(Man-Yeong Ha) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
In this paper we investigate two-dimensional laminar flow around freely rotating rectangular cylinders placed in a uniform stream. Numerical simulations are performed, using finite volume method, in the ranges of 50≤Re≤150 and 0.2≤W/H≤1.0, where Re and W/H are the Reynolds number and the width-to-height ratio, respectively. The immersed boundary method is used to handle the rectangular cylinder in a rectangular grid system. Comparisons with the previous results show good agreement in Strouhal number and rotational rate. The present study reports the detailed information of flow structure at different width-to-height ratios.
회전하는 원형 실린더 주위의 층류 유동장에 관한 수치적 연구
이용석(Yong Suk Lee),두정훈(Jeong Hoon Doo),하만영(Man Yeong Ha),윤현식(Hyun Sik Yoon) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
The present study numerically investigates three-dimensional laminar flow past a rotating circular cylinder placed in a uniform stream. For the purpose of a careful analysis of the modification of flow by the effect of the rotation on the flow, numerical simulations are performed at a various range of rotational speeds (0≤α≤2.5) at one Reynolds number of 300. As α increases, flow becomes stabilized and finally a steady state beyond the critical rotational speed. The 3D (three dimensional) wake mode of the stationary cylinder defined at this Reynolds number has been disorganized according to α, which were observed by the visualization of 3D vortical structures. The variation of the Strouhal number is significant when the wake pattern is changed according to the rotational speed. As α increases, the lift increases, whereas the drag decreases.
타원형 실린더의 각도 변화가 사각 밀폐계 내부의 자연대류 현상에 미치는 영향
손용진(Yong Jin Son),하만영(Man Yeong Ha) 대한설비공학회 2018 설비공학 논문집 Vol.30 No.2
This study investigated the effect of variation in the angle of the elliptic cylinder as well as the presence of circular cylinder on natural convection inside a square enclosure. The Rayleigh number was varied between 10<SUP>3</SUP> and 10<SUP>6</SUP>, and the Prandtl number was fixed to 0.7. In the present study, the angle of the elliptic cylinder was changed from 0° to 90°, and the perimeter of the elliptic cylinder was same as that of the circular cylinder. The immersed boundary method was used to capture the virtual wall boundary of the inner cylinder. With the increasing angle of the elliptic cylinder, the surface-averaged Nusselt numbers on the cylinder and the enclosure increased. In the Rayleigh number range considered in the present study, the surface-averaged Nusselt number on the elliptic cylinder over = 45° was higher than that of the circular cylinder. The effect of elliptic cylinder’s angle on natural convection in the enclosure was analyzed according to the flow and thermal fields, and the distributions of the Nusselt number.
Lid-Driven 캐비티 내의 혼합대류에 의한 원형 실린더의 운동 특성에 관한 수치적 연구
김다용(Da Yong Kim),윤현식(Hyun Sik Yoon),하만영(Man Yeong Ha) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5
본 논문은 좌측의 벽면이 일정한 속도로 움직이는 Lid-driven 캐비티 내의 혼합대류에 의에 부유하는 원형 실린더의 운동 특성 규명하는 연구를 수행하였다. 이차원 원형실린더의 운동 특성을 해석하기 위해 Direct forcing/Fictitious domain 방법을 사용하였다. Lid-driven 캐비티 내의 고체와 유체의 밀도 비에 따란 원형 실린더의 운동 특성을 연구하기 위해 밀도비를 변경하면서(0.97, 0.98, 0.99, 1.01, 1.02, 1.03) 수치해석을 수행하였으며 캐비티 내의 Richardson number는 1로 고정하였다. The present study numerically investigates the motion of a solid body suspended in the lid-driven cavity with mixed convection. Flows are driven by the left lid, which slides in its own plane constant velocty. A two-dimensional circular cylinder levitated thermally has been simulated by using the direct forcing /fictitious domain (DF/FD) method. In order to identify the effect of fluid density on circular cylinder motion in lid-driven cavity, the computation is carried out for wide ranges of the fluid density ratio (=0.97, 0.98, 0.99, 1.01, 1.02, 1.03) and fixed Richardson number (=1).
열 전달이 있는 2차원 채널에서 움직이는 원형 입자에 대한 수치적 연구
김다용(Da Yong Kim),윤현식(Hyun Sik Yoon),하만영(Man Yeong Ha) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
This paper reports the result of direct simulation of fluid-structure interaction (FSI) two dimensional channel with thermal convection. We performed numerical simulation about a isothermal circular particle for ρ<SUB>s</SUB>/ρ<SUB>f</SUB>=1.00232 where ρ<SUB>s</SUB>/ρ<SUB>f</SUB> denotes a particle to fluid density ratio in vertical channel having different temperatures on both walls. The cold or hot particle is initially located at a third of channel from top. The particle has been simulated by using the direct forcing/fictitious domain (DF/FD) method. The results of numerical study indicate that a circular particle motion can be classified into three regimes: steady settling close to one of the wall motion, stationary motion and levitating motion. The motion is significantly depended on the Grashof number and the effect of wall confinement.
난류 용탕 In-situ 합성 믹서의 설계 및 Cu-TiB<sub>2</sub> 나노 복합재료의 제조
최백부,박정수,윤지훈,하만영,박용호,박익민,Choi, Baek-Boo,Park, Jung-Su,Yun, Ji-Hun,Ha, Man-Young,Park, Yong-Ho,Park, Ik-Min 한국재료학회 2007 한국재료학회지 Vol.17 No.1
Turbulent in-situ mixing process is a new material process technology to get dispersed phase in nanometer size by controlling reaction of liquid/solid, liquid/gas, flow ana solidification speed simultaneously. In this study, mixing which is the key technology to this synthesis method was studied by computational fluid dynamics. For the simulation of mixing of liquid metal, static mixers investigated. Two inlets for different liquid metal meet ana merge like 'Y' shape tube having various shapes and radios of curve. The performance of mixer was evaluated with quantitative analysis with coefficient of variance of mass fraction. Also, detailed plots of intersection were presented to understand effect of mixer shape on mixing. The simulations show that the Reynolds number (Re) is the important factor to mixing and dispersion of $TiB_2$ particles. Mixer was designed according to the simulation, and $Cu-TiB_2$ nano composites were evaluated. $TiB_2$ nano particles were uniformly dispersed when Re was 1000, and cluster formation and reduction in volume fraction of $TiB_2$ were found at higher Re.