• Title/Summary/Keyword: 비 정렬 격자

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Numerical Simulation of 2-D Lid-Driven Cavity Plow at High Reynolds numbers (높은 Re수에서의 2차원 Lid-Driven 캐비티유동의 수치해석)

  • Myong H. K.;Kim J. E.
    • 한국전산유체공학회:학술대회논문집
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    • 2005.04a
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    • pp.153-158
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    • 2005
  • Numerical simulations of two-dimensional steady incompressible lid-driven flow in a square cavity are presented to verify the validity of a new solution code(PowerCFD) with unstructured grids. The code uses the non-staggered(collocated) grid approach which is very popular for incompressible flow analysis because of its numerical efficiency on the curvilinear or unstructured grids. Solutions are obtained for configurations with a Reynolds number as high as 10,000 with both rectangular and hybrid types of unstructured grid mesh. Interesting features of the flow are presented in detail and comparisons are made with benchmark solutions found in the literature. It is found that the code is capable of producing accurately the nature of the lid-driven cavity flow at high Reynolds numbers.

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IMPLEMENTATION OF A SECOND-ORDER INTERPOLATION SCHEME FOR THE CONVECTIVE TERMS OF A SEMI-IMPLICIT TWO-PHASE FLOW ANALYSIS SOLVER (물-기체 2상 유동 해석을 위한 Semi-Implicit 방법의 대류항에 대한 이차정확도 확장)

  • Cho, H.K.;Lee, H.D.;Park, I.K.;Jeong, J.J.
    • 한국전산유체공학회:학술대회논문집
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    • 2009.04a
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    • pp.290-297
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    • 2009
  • A two-phase (gas and liquid) flow analysis solver, named CUPID, has been developed for a realistic simulation of transient two-phase flows in light water nuclear reactor components. In the CUPID solver, a two-fluid three-field model is adopted and the governing equations are solved on unstructured grids for flow analyses in complicated geometries. For the numerical solution scheme, the semi-implicit method of the RELAP5 code, which has been proved to be very stable and accurate for most practical applications of nuclear thermal hydraulics, was used with some modifications for an application to unstructured non-staggered grids. This paper is concerned with the effects of interpolation schemes on the simulation of two-phase flows. In order to stabilize a numerical solution and assure a high numerical accuracy, the second-order upwind scheme is implemented into the CUPID code in the present paper. Some numerical tests have been performed with the implemented scheme and the comparison results between the second-order and first-order upwind schemes are introduced in the present paper. The comparison results among the two interpolation schemes and either the exact solutions or the mesh convergence studies showed the reduced numerical diffusion with the second order scheme.

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Numerical Analysis of Viscous Flows on Unstructured Grids Using the Optimal Method of Strongly Implicit Procedure (비정렬 격자계에서 S.I.P. 최적화 방법을 이용한 점성유동 수치해석)

  • Shin, Young-Seop
    • Journal of the Society of Naval Architects of Korea
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    • v.49 no.2
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    • pp.196-202
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    • 2012
  • In this study, numerical analysis of viscous flows is carried out based on the unstructured grid. There exist some difficulties in expressing and computing numerical derivatives on the unstructured grid due to lack of the structured characteristics. The general computer algorithms are developed to perform numerical derivatives easily and extended to be applicable to various geometries composed of hybrid meshes. And the optimal method of strongly implicit procedure is newly contrived to accelerate the rate of convergence in solving the pressure Poisson equation. To verify numerical schemes, the driven cavity problems of 2 and 3 dimension are simulated. The numerical results are compared with others and our numerical schemes are shown to be valid.

Robust and Efficient LU-SGS Scheme on Unstructured Meshes: Part Ⅱ - Efficient Implementation (비정렬 격자계에서 강건하고 효율적인 LU-SGS 기법 개발: Part Ⅱ- 효율적인 적용)

  • Kim Joo Sung;Kwon Oh Joon
    • Journal of computational fluids engineering
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    • v.9 no.3
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    • pp.39-48
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    • 2004
  • In the present study, an efficient implementation technique of the van Leer's implicit operator is suggested in accordance with the Roe's explicit operator. By using an efficient treatment of the off-diagonal terms, which occupy most of the memory requirement for the linear system of equations, it is shown that the improved scheme only requires less than 30% of memory and is approximately 10-20% faster than the baseline scheme.

Robust and Efficient LU-SGS Scheme on Unstructured Meshes: Part I - Implicit Operator (비정렬 격자계에서 강건하고 효율적인 LU-SGS 기법 개발: Part I - 내재적 연산자)

  • Kim Joo Sung;Kwon Oh Joon
    • Journal of computational fluids engineering
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    • v.9 no.3
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    • pp.26-38
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    • 2004
  • A study has been made for the investigation of the robustness and convergence of various implicit operators of the LU-SGS scheme using linear stability analysis. It is shown that the behavior of the implicit operator is not determined by its own characteristics, but is determined relatively depending on the dissipative property of the explicit operator. It is also shown that, as the dissipation level of the implicit operator increases, the robustness of the scheme increases, but the convergence rate can be deteriorated due to the excessive dissipation. The numerical results demonstrate that the dissipation level of the impliict operator needs to be higher than that of the explicit operator for computing stiff problems.

Calculation of Turbulent Flows Using an Implicit Scheme on Two-Dimensional Unstructured Meshes (2차원 비정렬 격자에서의 내재적 기법을 이용한 난류 유동 재산)

  • Kang Hee Jung;Kwon Oh Joon
    • Journal of computational fluids engineering
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    • v.2 no.2
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    • pp.26-34
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    • 1997
  • An implicit viscous turbulent flow solver is developed for two-dimensional geon unstructured triangular meshes. The flux terms are discretized based on a cell-centered formulation with the Roe's flux-difference splitting. The solution is advanced in time us backward-Euler time-stepping scheme. At each time step, the linear system of equation approximately solved wi th the Gauss-Seidel relaxation scheme. The effect of turbulence is with a standard k-ε two-equation model which is solved separately from the mean flow equation the same backward-Euler time integration scheme. The triangular meshes are generated advancing-front/layer technique. Validations are made for flows over the NACA 0012 airfoil. Douglas 3-element airfoil. Good agreements are obtained between the numerical result experiment.

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HIGH-ORDER ACCURATE SIMULATIONS OF BLADE-VORTEX INTERACTION USING A DISCONTINUOUS GALERKIN METHOD ON UNSTRUCTURED MESHES (비정렬 격자계에서 고차정확도 불연속 갤러킨 기법을 이용한 블레이드-와류 간섭 현상 모사)

  • Lee, H.D.;Kwon, O.J.
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03a
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    • pp.57-70
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    • 2008
  • A high-order accurate Euler flow solver based on a discontinuous Galerkin finite-element method has been developed for the numerical simulations of blade-vortex interaction phenomena on unstructured meshes. A free vortex in freestream was investigated to assess the vortex-preserving property and the accuracy of the present flow solver. Blade-vortex interaction problems in subsonic and transonic freestreams were simulated by adopting a multi-level solution-adaptive dynamic mesh refinement/coarsening technique. The results were compared with those of other numerical and experimental methods. It was shown that the present discontinuous Galerkin flow solver can preserve the vortex structure for significantly longer vortex convection time and can accurately capture the complex unsteady blade-vortex interaction flows, including generation and propagation of acoustic waves.

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A STUDY ON AN INTERFACE CAPTURING METHOD APPLICABLE TO UNSTRUCTURED MESHES FOR THE ANALYSIS OF FREE SURFACE FLOW (자유표면유동 해석을 위한 비정렬격자계에 적합한 경계면포착법 연구)

  • Myong, H.K.;Kim, J.E.
    • Journal of computational fluids engineering
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    • v.11 no.4 s.35
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    • pp.14-19
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    • 2006
  • A conservative finite-volume method for computing 3-D flow with an unstructured cell-centered method has been extended to free surface flows or two-fluid systems with topologically complex interfaces. It is accomplished by implementing the high resolution method(CICSAM) by Ubbink(1997) for the accurate capturing of fluid interfaces on unstructured meshes, which is based on the finite-volume technique and is fully conservative. The calculated results with the present method are compared to show the ease and accuracy with available numerical and experimental results reported in the literature.

DEVELOPMENT OF A LARGE EDDY SIMULATION METHOD ON UNSTRUCTURED MESHES (비정렬 격자를 이용한 LES 기법 개발)

  • Lee, K.S.;Baek, J.H.
    • 한국전산유체공학회:학술대회논문집
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    • 2006.10a
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    • pp.106-109
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    • 2006
  • A large eddy simulation with explicit filters on unstructured mesh is presented. Two explicit filters are adopted for reducing the aliasing error of the nonlinear convective term and measuring the level of subgrid scale velocity fluctuation, respectively. The developed subgrid scale model is basically eddy viscosity model which depends on the explicitly filtered fields and needs no additional ad hoc wall treatment such as van Driest damping function. As a validation problem, the flows around a sphere at several Reynolds numbers, including laminar and turbulent regimes, are calculated and compared to experimental data and numerical results in the literature.

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HIGH-ORDER ACCURATE SIMULATIONS OF BLADE-VORTEX INTERACTION USING A DISCONTINUOUS GALERKIN METHOD ON UNSTRUCTURED MESHES (비정렬 격자계에서 고차정확도 불연속 갤러킨 기법을 이용한 블레이드-와류 간섭 현상 모사)

  • Lee, H.D.;Kwon, O.J.
    • 한국전산유체공학회:학술대회논문집
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    • 2008.10a
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    • pp.57-70
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    • 2008
  • A high-order accurate Euler flow solver based on a discontinuous Galerkin finite-element method has been developed for the numerical simulations of blade-vortex interaction phenomena on unstructured meshes. A free vortex in freestream was investigated to assess the vortex-preserving property and the accuracy of the present flow solver. Blade-vortex interaction problems in subsonic and transonic freestreams were simulated by adopting a multi-level solution-adaptive dynamic mesh refinement/coarsening technique. The results were compared with those of other numerical and experimental methods. It was shown that the present discontinuous Galerkin flow solver can preserve the vortex structure for significantly longer vortex convection time and can accurately capture the complex unsteady blade-vortex interaction flows, including generation and propagation of acoustic waves.

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