• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.622-625
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• 2008

While the research for flow over a circular cylinder has been actively carried out up to the present, it has been known that the flow has not been clarified even now. Various complex flow and aero-acoustic characteristics exist around a circular cylinder such as flow separation, wake and pressure wave propagation. In this paper, research was carried out for wake flow and aeroacoustics over a circular cylinders by using high order, high resolution techniques that are used in two dimensional aero- acoustic analysis. OpenMP parallel processing method was used. For the numerical result, the periodic characteristic of Strouhal Number due to vortex shedding was comparatively analyzed with other experiment values and two dimensional numerical results.

• 대한기계학회논문집
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• 제17권6호
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• pp.1518-1528
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• 1993

본 연구는 단일 원주의 와여기 진동특성에 관한 연구의 연속연구로서 풍동내 에 직렬로 배열된 두 원주의 직교유동에 의한 두 가지 경우의 동적 거동을 조사하였다. 첫째는 상류측 탄성지지 원주의 후류내에 가깝게 놓여진 하류측 고정원주의 간섭에 의한 상류측 원주의 진동(proximity-induced vibration)이며, 둘째는 상류측의 고정원 주의 후류내에 가깝게 놓여진 하류측 탄성지지 원주의 공기역학적 진동(wake-induced vibration)이다. 본 연구의 목적으로 직렬로 배열된 동일 직경의 두 원주에 있어서 어느 한 쪽의 원주가 탄성지지가 되어 있을 경우, 두 원주사이의 간격과 유속변화에 따른 와여기 진동과 유력탄성 불안정 진동의 진동특성 및 후류내에서의 와유출 특성을 명확히 하기 위해 실험적으로 조사, 연구하였다.

• 설비공학논문집
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• 제15권12호
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• pp.1095-1102
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• 2003

Flow characteristics of turbulent steady fluid flow past a cylinder in rectangular duct are measured by 5 W laser doppler velocity meter. The fluid flow is also computed by commercial software of STAR-CD for comparison between the measurement and computation. The turbulent models applied in the computations are standard K-epsilon model, RNG K-epsilon model and Chen K-epsilon model. Acurracy of standard K-epsilon model is a little bit better than acurracies of other models even though those models have almost the same order of error compared to measured data. The computations predict satisfactorily the measured velocity profiles at middle section of the circular cylinder before the fluid flow diverges. However, there are some disagreements between them at down stream from the circular cylinder.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1460-1465
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• 2004

Flow patterns around a rotating circular cylinder having square dimpled surface were visualized by the hydrogen bubble technique at velocity ratios from a=0 to 4.8 and Reynolds number of $Re=1.0{\times}10^{4}$. The wake region of the cylinder was reduced as the velocity ratios increase and was smaller than that of the smooth cylinder without dimples at the same velocity ratio. The hydrodynamic characteristics on the cylinder was investigated by measuring of lift and drag at velocity ratios from a=0 to 4.1 and Reynolds number from $Re=1.2{\times}10^{4}$ to $Re=2.0{\times}10^{4}$. As the velocity ratios increase, the average lift and drag coefficients were increased and at the same velocity ratio, the average lift was larger but the average drag was smaller than that of the smooth cylinder.

• 대한기계학회논문집B
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• 제28권4호
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• pp.486-492
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• 2004

Flow patterns around a rotating circular cylinder having square dimpled surface were visualized by the hydrogen bubble technique at velocity ratios from a=0 to 4.8 and Reynolds number of Re=1.0${\times}$10$^4$. The wake region of the cylinder was reduced as the velocity ratios increase and was smaller than that of the smooth cylinder without dimples at the same velocity ratio. The hydrodynamic characteristics on the cylinder was investigated by measuring of lift and drag at velocity ratios from a=0 to 4.1 and Reynolds number from Re=1.2${\times}$10$^4$ to Re=2.0${\times}$10$^4$. As the velocity ratios increase, the average lift and drag coefficients were increased and at the same velocity ratio, the average lift was larger but the average drag was smaller than that of the smooth cylinder.

• Wind and Structures
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• 제19권4호
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• pp.389-404
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• 2014

The flow characteristics of a circular cylinder surrounded by an outer permeable cylinder were experimentally investigated using Particle Image Velocimetry Technique in deep water flow. In order to consider the effects of diameter and porosity of the outer cylinder on flow structures of the inner cylinder, five different outer cylinder diameters (D=37.5, 52.5, 60, 75 and 90 mm) and eight different porosities (${\beta}$=0.4, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8 and 0.85) were selected. During the experiments, the diameter of inner cylinder was kept constant as d=30 mm. The depth-averaged free-stream velocity was adjusted as U=0.156 m/s, which corresponds to the Reynolds number of Re=5000 based on the inner cylinder diameter. It has been concluded that both the outer permeable cylinder diameter and the porosity have important influences on the attenuation of vortex shedding in the wake region. The presence of outer permeable cylinder decreases the magnitude of Reynolds shear stress and turbulent kinetic energy compared to the bare cylinder case. Moreover, the spectral analysis of vortex shedding frequency has revealed that the dominant frequency of vortex shedding downstream of the cylinder arrangement also reduces substantially due to the weakened Karman shear layer instability.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.582-587
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• 2001

A numerical method using FLUENT code was employed to investigate fluid drag and lift forces on a cylinder in a group of circular cylinders, subjected to a uniform cross flow. The cylinders can be arranged in tandem or in a staggered arrangements relative to the free stream flow. A vortex street behind the cylinder pairs or jets between the cylinders forms according to the arrangements. Vibration on a cylinder can occurs due to vortex shedding, fluid-elastic stiffness and wake galloping. The flow is first investigated and then the forces acting on the cylinder are calculated. The lift and drag forces on an elastically mounted cylinder in the wake of an upstream fixed cylinder arise from the mean flow plus velocity and pressure gradients in the wake. The analytical results of two staggered cylinder were compared with the existing experimental ones for validation of the present method. The analytical results of the forces were in good agreement with the experimental ones. The present method can be used for the analysis of the fluid induced vibration where the group of circular cylinders are subjected to a cross flow.

• 설비공학논문집
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• 제30권2호
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• pp.58-67
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• 2018

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 $10^3$ and $10^6$, and the Prandtl number was fixed to 0.7. In the present study, the angle of the elliptic cylinder was changed from $0^{\circ}$ to $90^{\circ}$, 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 = $45^{\circ}$ 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.

• 대한기계학회논문집B
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• 제21권7호
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• pp.882-890
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• 1997

A buoyant jet flow impinging on a circular cylinder is investigated including heat conduction through the cylinder. Temperature and flow fields are obtained by an iterative method, and the effects of the non-uniform wall temperature on the flow and heat transfer are analyzed. Effects of three-dimensionality and the traversing of the jet are also included. Nusselt number over the cylinder surface for the conjugate case is relatively small as compared with the constant wall temperature case due to the small temperature gradient. As the conductivity of the cylinder becomes lower, Nusselt number decreases due to the reduced temperature gradient. Increasing jet traversing speed causes the surface temperature of the cylinder to decrease, which increases local Nusselt number over the surface.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2489-2494
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• 2008

The two-dimensional circular cylinder freely falling in a channel has been simulated by using Immersed boundary - lattice Boltzmann method in order to analyze the characteristics of motion originated by the interaction between the fluid and the solid. The wide range of the solid/fluid density ratio has been considered to identify the effect of the solid/fluid density ratio on the motion characteristics such as the falling time, the terminal velocity and the trajectory in the vertical and horizontal directions. In addition, the effect of the gap between the cylinder and the wall on the motion of two-dimensional circular cylinder freely falling has been revealed by taking into account a various range of the gap size. The Reynolds number in terms of the terminal velocity is diminished as the cylinder becomes close to the wall at the initial dropping position, since the repulsive force induced between the cylinder and wall constrains the vertical motion. Quantitative information about the flow variables such as the pressure coefficient and vorticity on the cylinders is highlighted.