• 제목/요약/키워드: Vertical Cylinder

검색결과 227건 처리시간 0.024초

일정 열유속 실린더를 갖는 수평 환형 공간에서의 공기의 이중 자연대류 유동 (Dual Natural-Convective Flows of Air in a Horizontal Annulus with a Constant Heat Flux Cylinder)

  • 유주식
    • 한국전산유체공학회지
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    • 제4권2호
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    • pp.1-8
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    • 1999
  • Natural convection in a horizontal annulus with the inner cylinder heated by the application of a constant heat flux and the isothermally cooled outer cylinder is considered, and the transition of flows and the bifurcation phenomenon are numerically investigated for air with Pr=0.7. The zero initial condition always induces a crescent-sheped eddy flow. A bicellular flow in which the fluid descends along the vertical central plane of the annulus can be obtained at high Rayleigh number by introducing artificial numerical disturbances. Dual solutions are found above a certain critical Rayleigh number. Hysteresis phenomena have not been observed.

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불안정 성층화를 가진 원통형 용기 내의 회전유동에 관한 연구 (Rotating Flows in a Circular Cylinder with Unstable Stratification)

  • 김재원
    • 한국전산유체공학회지
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    • 제3권2호
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    • pp.27-38
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    • 1998
  • Rotating flow of a stratified fluid contained in a circular cylinder with unstable temperature gradient imposed on the side wall of it has been numerically studied. The temperatures at the endwall disks are constant. The top disk of the container is coider than that of the bottob disk, as much as the temperature difference n${\Delta}$T, (0${\leq}$n${\leq}$3). Flows in the vessel are driven by an impulsive rotation of the hot bottom disk with respect to the central axis of the cylinder. Flow details have been acquired. For this flow, the principal balance in the interior core is characterized by a relationship between the radial temperature gradient and the vertical shear in the azimuthal velocity. As the buoyancy effect becomes appreciable, larger portions of the meridional fluid transport are long-circuit from the bottom disk to the interior region via the side wall.

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회전요동하는 원통내의 유동특성 - 이론적 해석 (Fluid Flow in a Circular Cylinder Subject to Circulatory Oscillation-Theoretical Analysis)

  • 서용권;김현민
    • 대한기계학회논문집B
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    • 제20권12호
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    • pp.3960-3969
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    • 1996
  • A fluid flow inside a circular cylinder subject to horizontal and circular oscillation is analyzed theoretically. Under the assumption of small-amplitude oscillation, the governing equations take linear forms. The velocity field is obtained in terms of the first kind of Bessel function of order 1. It was found that a particle describes an orbit close to a circle in the central region and an arc near the side wall. We also obtained the Stokes' drift velocity induced by the traveling wave along the circumferential direction. The Eulerian streaming velocities at the edge of the bottom and side boundary layers were also obtained. It was shown that the vertical component of the steady streaming velocity on the side wall is almost proportional to the amplitude of the free surface motion.

방위각방향 온도변화를 가지는 실린더 내의 부력 유동 (Buoyant Convection in a Cylinder with Azimuthally-varying Sidewall Temperature)

  • 정광효;현재민;송태호
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2000년도 춘계학술대회논문집B
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    • pp.45-50
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    • 2000
  • A numerical investigation is made of three-dimensional buoyant convection of a Boussinesq-fluid in a vertical cylinder. The top and bottom endwalls are thermally insulated. Flow is driven by the substantial azimuthal variations in thermal boundary conditions. Comprehensive numerical solutions to the Navier-Stokes equations are obtained. The representative Rayleigh number is large, thus, the overall flow pattern is of boundary layer-type. Three-dimensional (low characteristics are described. Specially, the global flow and the heat transfer features are delineated when the severity of azimuthal variation of sidewall temperature n, is intensified. Temperature and velocity fields on the meridional planes and the planes of constant height are presented. The global flow weakens as n becomes large. The pattern of the local Nusselt number on the surface of cylinder is similar regardless of n. The convective gain in heat transfer activities is reduced as n increases.

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원통 내 수평 보텍스 링의 거동 (Movement of a Horizontal Vortex Ring in a Circular Cylinder)

  • 여창호;서용권
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2003년도 추계학술대회
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    • pp.640-645
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    • 2003
  • In this paper, we report the numerical and experimental solutions of the vortical flows driven by an impingement of fluid from the bottom wall of a circular cylinder. We managed to visualize successfully the flow pattern shown on the vertical plane through the container axis. The numerical results are shown to compare well with the experimental results for the case of infinity Rossby number. The satisfactory agreement between the two results was possible when in the numerics the free surface was treated as a solid wall so that a no-slip condition was applied on the surface. The numerical solutions reveal that inertial oscillation plays an important role at small Rossby numbers, or at a large background rotation.

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회전하는 원형단면 실린더 주위의 난류유동 물질전달에 대한 직접수치모사 ( I ) - 높은 Schmidt 수에 대하여 - (Direct Numerical Simulation of Mass Transfer in Turbulent new Around a Rotating Circular Cylinder ( I ) - At Sc=1670 -)

  • 황종연;양경수
    • 대한기계학회논문집B
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    • 제29권7호
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    • pp.837-845
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    • 2005
  • In this paper, an investigation on high-Schmidt number (Sc=1670) mass transfer in turbulent flow around a rotating circular cylinder is carried out by Direct Numerical Simulation. The concentration field is computed for three different values of low Reynolds number, namely 161, 348 and 623 based on the cylinder radius and friction velocity. Statistical study reveals that the thickness of Nernst diffusive layer is very small compared with that of viscous sub-layer in the case of high Sc mass transfer. Strong correlation of concentration field with streamwise and vertical velocity components is observed. However, that is not the case with the spanwise velocity component. Instantaneous concentration visualization reveals that the length scale of concentration fluctuation typically decreases as Reynolds number increases. Statistical correlation between Sherwood number and Reynolds number is consistent with other experiments currently available.

Exploration of power take off in wave energy converters with two-body interaction

  • Wang, Hao;Sitanggang, Khairil;Falzarano, Jeffrey
    • Ocean Systems Engineering
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    • 제7권2호
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    • pp.89-106
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    • 2017
  • The study explores a novel design of wave energy converter (WEC) that utilizes the interaction between an inside heaving vertical cylinder with an outside fixed hollow cylinder. This design originates from the oscillating water column (OWC) type WEC but replaces the pneumatic power take off (PTO) through the Wells turbine with the hydrodynamic PTO through the inside heaving cylinder. To effectively evaluate the maximum power output, the system has been modeled in the hydrodynamic software AQWA (developed by ANSYS Inc) that has accumulated extensive offshore industry users. Ranges of the PTO parameters have been examined to make sure that proper linear damping can be implemented to simulate the PTO force. Comparing the efficiency of the pneumatic PTO with the hydrodynamic PTO, it appears that the hydrodynamic PTO is more promising than the traditional Wells turbine for an OWC system.

조수 및 소수력 발전을 위한 회수를 위한 중력엔진의 개념 및 에너지 정산 (A Concept and Energy performance of a Gravity Engine for Tidal and Hydro-Power)

  • Lee, Jae-Young
    • 한국에너지공학회:학술대회논문집
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    • 한국에너지공학회 1999년도 추계 학술발표회 논문집
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    • pp.231-236
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    • 1999
  • This paper is to propose a concept and performance of the gravity engine which could extract energy from sea or river as a clean and renewable and sustainable power, the tidal or hydro-power. The vertical motion of the buoyancy cylinder of the present gravity engine is converted to the mechanical work directly without any hydraulic loss. The increased gravity potential during high tide is harnessed proportional to the length of the buoyancy cylinder times tidal height which is greater than the conventional tidal power using water mill. This energy amplification results from the net energy gain between the resource energy and the imposed energy to extract water out of the buoyancy cylinder. Its efficiency is higher than the conventional water mill due to its direct mechanical conversion.

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Application of Immersed Boundary Method for Flow Over Stationary and Oscillating Cylinders

  • Lee Dae-Sung;Ha Man-Yeong;Kim Sung-Jin;Yoon Hyun-Sik
    • Journal of Mechanical Science and Technology
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    • 제20권6호
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    • pp.849-863
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    • 2006
  • IBM (Immersed Boundary Method) with feedback momentum forcing was applied to stationary and moving bodies. The capability of IBM to treat the obstacle surfaces, especially with moving effect has been tested for two dimensional problems. Stationary and oscillating cylinders were simulated by using IBM based on finite volume method with Cartesian coordinates. For oscillating cylinder, lateral and vertical motions are considered, respectively. Present results such as time histories of drag and lift coefficients for both stationary and oscillating cases are in good agreement with previous numerical and experimental results. Also, the instantaneous wake patterns of oscillating cylinder with different oscillating frequency ratios well represented those of previous researches. More feasibility study for IBM has been carried out to two oscillating cylinders. Drag and lift coefficients are presented for two cylinders oscillating sinusoidally with phase difference of $180^{\circ}$.

인공 폐 보조장치 내에서의 유체 유동 모델링에 대한 연구 (Study on the Fluid Dynamics Modeling in Artificial Lung Assist Device)

  • 김기범;박영란;김상진;홍철운;강형섭;김진상;김성종;김민호
    • Korean Chemical Engineering Research
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    • 제49권2호
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    • pp.230-237
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    • 2011
  • 본 연구에서는 혈관 내 인공 폐(intravenous lung assist device)를 개발하기 위하여 CFD를 사용하여 새로운 형태의 인공 폐 모형에 대한 유체의 흐름 특성을 모델링하였다. 모델링을 위하여 중공사(hollow fiber)는 무시하였으며 vertical type과 tangential type이 모델로 사용되었다. 유체의 흐름 특성을 예측하기 유체의 입출구로 1개로 하였을 때와 2개로 하였을 때 그리고 입출구를 관의 중심부(vertical)와 관 벽의 접선방향(tangential)에 위치하였을 때의 흐름 특성을 파악 하였다. 실험 결과, tangential type과 같이 원통의 접선 방향으로 유체의 입구와 출구를 설정할 경우 vertical type에서 나타나는 흐름이 없는 영역(정체층)을 제거할 수 있었다. 또한 tangential type은 와류형태의 흐름이 지배적이며 한쪽으로 편중된 흐름이 아닌 복잡한 형태의 흐름이 발생하는 것으로 나타났다. 또한 유체의 입출구가 2개일 때 유체가 편중된 흐름이 발생하지 않고 관 전체에 복잡한 형태로 흐름이 발생하는 것으로 나타났다. 실험 결과를 통하여 우리는 유체가 유입되는 입구와 출구가 tangential type이며 각각 2개일 때 유체의 흐름이 복잡하며 정체층이 발생하지 않는 흐름이 발생한다는 것을 확인할 수 있었다.