• Title/Summary/Keyword: Staggered grid

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The Basic Study on the Technique of Fluid Flow Analysis Using the Immersed Boundary Method (가상 경계 방법을 이용한 유동 해석 기법에 관한 기초 연구)

  • Yang, Seung-Ho;Ha, Man-Yeong;Park, Il-Ryong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.6
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    • pp.619-627
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    • 2004
  • In most industrial applications, the geometrical complexity is combined with the moving boundaries. These problems considerably increase the computational difficulties since they require, respectively, regeneration and deformation of the grid. As a result, engineering flow simulation is restricted. In order to solve this kind of problems the immersed boundary method was developed. In this study, the immersed boundary method is applied to the numerical simulation of stationary, rotating and oscillating cylinders in the 2-dimensional square cavity. No-slip velocity boundary conditions are given by imposing feedback forcing term to the momentum equation. Besides, this technique is used with a second-order accurate interpolation scheme in order to improve the accuracy of flow near the immersed boundaries. The governing equations for the mass and momentum using the immersed boundary method are discretized on the non-staggered grid by using the finite volume method. The results agree well with previous numerical and experimental results. This study presents the possibility of the immersed boundary method to apply to the complex flow experienced in the industrial applications. The usefulness of this method will be confirmed when we solve the complex geometries and moving bodies.

Effect of DVI Nozzle Location on the Thermal Mixing in the RVDC (DVI 노즐 위치가 원자로 하향유로내의 냉각수 열적혼합에 미치는 영향 분석)

  • Kang Hyung Seok;Cho Bong Hyun;Kim Hwan Yeol;Yoon Juhyeon;Bae Yoon Yeong
    • Journal of computational fluids engineering
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    • v.3 no.1
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    • pp.89-99
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    • 1998
  • 한국형 차세대원자로에서는 비상노심 안전주입수가 저온관을 통하지 않고 원자로용기에 직접 주입된다. 원자로용기의 가압열충격과 열수력적 관점에서 최적의 노즐위치를 결정하기 위해서 전산유체역학을 활용하였다. 상용 전산유체코드인 CFX를 이용하여 원자로 하향유로를 모사하는 해석대상 격자를 다중불록으로 형성한 다음 유동장을 비압축성 Navier-Stokes 운동량 방정식, 에너지 방정식과 표준 k-ε 난류모형 등으로 모형화하여 3차원 비정상상태 계산을 수행하였다. CFX에서는 경계 밀착좌표계, 비엇물림격자와 SIMPLE 알고리즘을 사용한다. 본 연구결과 원자로용기의 가압열충격 관점에서 가장 보수적인 사고인 증기관 파단사고시에도 열적혼합이 잘 일어나 가압열충격이 발생할 가능성이 없는 것으로 판단되며 안전주입수 노즐이 저온관 바로 위에 위치할 때 원자로 하향유로 내의 온도 분포가 가장 균일하여 열적 혼합 관점에서는 최적의 위치로 판단된다.

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A Study on the Selection of Dependent Variables of Momentum Equations in the General Curvilinear Coordinate System for Computational Fluid Dynamics (전산유체역학을 위한 일반 곡률좌표계에서 운동량 방정식의 종속변수 선정에 관한 연구)

  • Kim, Won-Kap;Choi, Young Don
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.2
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    • pp.198-209
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    • 1999
  • This study reports the selection of dependent variables for momentum equations in general curvilinear coordinates. Catesian, covariant and contravariant velocity components were examined for the dependent variable. The focus of present study is confined to staggered grid system Each dependent variable selected for momentum equations are tested for several flow fields. Results show that the selection of Cartesian and covariant velocity components intrinsically can not satisfy mass conservation of control volume unless additional converting processes ore used. Also, Cartesian component can only be used for the flow field in which main-flow direction does not change significantly. Convergence rate for the selection of covariant velocity component decreases quickly as with the increase of non-orthogonality of grid system. But the selection of contravariant velocity component reduces the total mass residual of discretized equations rapidly to the limit of machine accuracy and the solutions are insensitive to the main-flow direction.

Velocity and Pressure Measurement of Channel Cavity Flow by PTV (PTV에 의한 채널캐비티 유동의 속도 및 압력계측)

  • Cho, D.H.;Kim, J.G.;Lee, Y.H.
    • Solar Energy
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    • v.17 no.3
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    • pp.59-66
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    • 1997
  • The present study adopted the PTV method for the velocity acquisition. The system consists of an image grabber built-in a personal computer and a laser-based sheet light projector and particle identification softwares. Velocity vectors are obtained, by PTV and they are used as velocity components for Poisson equation for pressure. Related boundary conditions and no-slip condition at solid wall and the linear velocity extrapolation on the upper side of cavity are well examined for the present study. For calculation of pressure, resolution of grid is basically $40{\times}40$ and 2-dimensional uniform mesh using MAC staggered grid is adopted. The result of experiment reveal that, newly suggested measuring method is capable of estimating pressure and velocity distribution of flow field reasonably.

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A Study on the Choice of Dependent Variables of Momentum Equations in the General Curvilinear Coordinate (일반곡률좌표계 운동량방정식의 종속변수 선정에 관한 연구)

  • Kim, Tak-Su;Kim, Won-Gap;Kim, Cheol-Su;Choe, Yeong-Don
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.11
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    • pp.1500-1508
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    • 2001
  • This paper represents the importance of dependent variables in non-orthogonal curvilinear coordinates just as the importance of those variables of convective scheme and turbulence model in computational fluid dynamics. Each of Cartesian, physical covariant and physical contravariant velocity components was tested as the dependent variables of momentum equations in the staggered grid system. In the flow past a circular cylinder, the results were computed to use each of three variables and compared to experimental data. In the skewed driven cavity flow, the results were computed to check the grid dependency of the variables. The results used in Cartesian and physical contravariant components of velocity in cylinder flow show the nearly same accuracy. In the case of Cartesian and contravariant component, the same number of vortex was predicted in the skewed driven cavity flow. Vortex strength of Cartesian component case has about 30% lower value than that of the other two cases.

A Study on Flow Characteristics of Two-Dimensional Backward-Facing Step by CFD (CFD에 의한 2차원 후향계단에서의 재부착 유동특성에 관한 연구)

  • 이영호
    • Journal of Advanced Marine Engineering and Technology
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    • v.23 no.1
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    • pp.9-18
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    • 1999
  • The present study is aimed to investigate flow characteristics of two-dimensional backward-fac-ing step by numerical approach. A convection conservation difference scheme based upon SOLA algorithm is used for the solution of the two-dimensional incompressible Navier-Stokes equations to simulate the laminar transitional and trubulent flow conditions at which the experimental data can be available for the backlward-facing step. The twenty kinds of reynolds number are used for the calculations. In an effort to demonstrate that the reported solutions are dependent on the mesh refinement computations are performed on seven different meshes of uniformly increasing refinement. also to investigate the result of inflow dependence two kinds of the inflow profile are chosen for the laminar flow. Irregular grid is adopted to minimize the errors on the satis-faction fo the discretized continuity. As criterion of benchmarking the result of numerical simula-tion reattachment lengthis used for the selected Reynolds numbers. The results of the present study prove the fact that the numerical predictions agree well with the experimental data and the flow characteristics are shown at the backward-facing step.

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The study of the characteristics of the stationary, rotating and oscillating cylinders using the immersed boundary method (가상 경계 방법을 이용한 정지, 회전 및 진동하는 실린더의 유동 특성에 관한 연구)

  • Yang, Seung-Ho;Ha, Man-Yeong;Park, Il-Ryong
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.916-921
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    • 2003
  • In most industrial applications, the geometrical complexity is combined with the moving boundaries. These problems considerably increase the computational difficulties since they require, respectively, regeneration and deformation of the grid. As a result, engineering flow simulation is restricted. In order to solve this kind of problems the immersed boundary method was developed. In this study, the immersed boundary method is applied to the numerical simulation of stationary, rotating and oscillating cylinders in the 2-dimensional square cavity. No-slip velocity boundary conditions are given by imposing feedback forcing term to the momentum equation. Besides, this technique is used with a second-order accurate interpolation scheme in order to improve the accuracy of flow near the immersed boundaries. The governing equations for the mass and momentum using the immersed boundary method are discretized on the non-staggered grid by using the finite volume method(FVM). This study presents the possibility of the immersed boundary method to apply to the complex flow experienced in the industrial applications.

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Numerical study for performance analysis and design of a counterflow type cooling tower (대향류형 냉각탑에 대한 설계 및 성능해석을 위한 수치해석적 연구)

  • 이상윤;이정희;최영기;유홍선
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.10 no.5
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    • pp.535-549
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    • 1998
  • A numerical study for performance analysis of a counterflow type forced draft tower and natural draft cooling tower has been performed based on the method using the finite volume method with non-orthogonal body fitted and non-staggered grid system. For solving the coupling problem between water and air, air enthalpy balance, moisture fraction balance, water enthalpy balance, and water mass balance equations are solved with Navier-Stoke’s equations simultaneously. For the effect of turbulence, the standard k-$\varepsilon$ turbulent model is implied in this analysis. The predicted result of the present analysis is compared with the experimental data and the commercial software result to validate the present study, The predicted results show good agreement with the experimental data and the commercial software result. To investigate the influence of the cooling tower design parameters such as approach, range and wet bulb temperature, parametric studies are also peformed.

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Numerical Study for the Performance Analysis and Design of a Crossflow- Type Forced Draft Cooling Tower

  • Choi, Young-Ki;Kim, Byung-Jo;Lee, Sang-Yun;Lee, Jung-Hee
    • International Journal of Air-Conditioning and Refrigeration
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    • v.8 no.1
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    • pp.1-13
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    • 2000
  • A numerical study for performance analysis of a crossflow-type forced draft cooling tower has been performed based on the finite volume method with non-orthogonal body fitted, and non-staggered grid system. For solving the coupling problem between water and air, air enthalpy, moisture fraction, water enthalpy, and water mass balance equations are solved with Navier-Stoke's equations simultaneously. For the effect of turbulence, the standard k-$\varepsilon$ turbulent model is implied in this analysis. The predicted result of the present analysis is compared with the experimental data and the commercial software result to validate the present study. The predicted results show good agreement with the experimental data and the commercial software result. To investigate the influence of the cooling tower design parameters such as approach, range and wet bulb temperature, parametric studies are also performed.

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The Theory of Smoke Movement by a Fire in an Enclosure (밀폐공간에서의 화재에 의한 연기의 유동 이론)

  • 노재성;유홍선
    • Proceedings of the Korea Institute of Fire Science and Engineering Conference
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    • 1996.11a
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    • pp.5-9
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    • 1996
  • In foreign country such as U.S.A and Japan, considerable research has been done regarding the spread of smoke in room of fire involvement by using computer. But, in our country it has not been. So, this paper presents a detailed qualitative description of phenomena which occures during typical fire scenarios through numerical analysis. This research, in the view of field model, is focused on finding out the smoke movement and temperature distribution. And it is planned to analyze governing equation including smoke diffusion equation by numerical analysis with finite volume method and non-staggered grid system. The SIMPLE method for pressure-velocity couple and power-law scheme for convection terms are used. It shows that a plume is formed, hot plume is formed, hot plume gases impinge on the ceiling and they spread across it. then, it eventually reaches the bounding walls of the enclosure. It takes 60s for smoke to fill the enclosure.

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