• Title/Summary/Keyword: Unstructured Grid

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LEAST-SQUARE SWITCHING PROCESS FOR ACCURATE AND EFFICIENT GRADIENT ESTIMATION ON UNSTRUCTURED GRID

  • SEO, SEUNGPYO;LEE, CHANGSOO;KIM, EUNSA;YUNE, KYEOL;KIM, CHONGAM
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.24 no.1
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    • pp.1-22
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    • 2020
  • An accurate and efficient gradient estimation method on unstructured grid is presented by proposing a switching process between two Least-Square methods. Diverse test cases show that the gradient estimation by Least-Square methods exhibit better characteristics compared to Green-Gauss approach. Based on the investigation, switching between the two Least-Square methods, whose merit complements each other, is pursued. The condition number of the Least-Square matrix is adopted as the switching criterion, because it shows clear correlation with the gradient error, and it can be easily calculated from the geometric information of the grid. To illustrate switching process on general grid, condition number is analyzed using stencil vectors and trigonometric relations. Then, the threshold of switching criterion is established. Finally, the capability of Switching Weighted Least-Square method is demonstrated through various two- and three-dimensional applications.

NUMERICAL SIMULATION OF LID-DRIVEN FLOW IN A SQUARE CAVITY AT HIGH REYNOLDS NUMBERS (정사각 캐비티내 고레이놀즈수 Lid-Driven 유동의 수치해석)

  • Myong H. K.
    • Journal of computational fluids engineering
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    • v.10 no.4 s.31
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    • pp.18-23
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    • 2005
  • Numerical simulations of two-dimensional steady incompressible lid-driven flow in a square cavity are presented by a new solution code(PowerCFD) which adopts an unstructured cell-centered method. Solutions are obtained for configurations with a Reynolds number as high as 10,000 with both rectangular and hybrid types of unstructured grid mesh in order to validate the code's independency of grid type. 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 with no grid type dependency.

Unstructured discretisation of a non-local transition model for turbomachinery flows

  • Ferrero, Andrea;Larocca, Francesco;Bernaschek, Verena
    • Advances in aircraft and spacecraft science
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    • v.4 no.5
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    • pp.555-571
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    • 2017
  • The description of transitional flows by means of RANS equations is sometimes based on non-local approaches which require the computation of some boundary layer properties. In this work a non-local Laminar Kinetic Energy model is used to predict transitional and separated flows. Usually the non-local term of this model is evaluated along the grid lines of a structured mesh. An alternative approach, which does not rely on grid lines, is introduced in the present work. This new approach allows the use of fully unstructured meshes. Furthermore, it reduces the grid-dependence of the predicted results. The approach is employed to study the transitional flows in the T106c turbine cascade and around a NACA0021 airfoil by means of a discontinuous Galerkin method. The local nature of the discontinuous Galerkin reconstruction is exploited to implement an adaptive algorithm which automatically refines the mesh in the most significant regions.

Multi-dimensional Finite-Volume Flow Computation Using Unstructured Grid (비정렬격자 다차원 FVM유동계산)

  • Kim J. K.;Chang K.-S.
    • 한국전산유체공학회:학술대회논문집
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    • 1995.10a
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    • pp.182-187
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    • 1995
  • The present paper explains some advancement made by the authors for the compressible flow computation of the Euler equations based on the unstructured grid and vertex- centered finite volume method. Accurate solutions to the unsteady axisymmetric shock wave propagation problems and three-dimensional airplane flows have been obtained by a high-order upwind TVD and FCT schemes. Unstructured grid adaption is made for the unsteady shock wave problems by the dynamic h-refinement/unrefinement procedure and for the three-dimensional steady flows by the Delaunay point-insertion method to generate three-dimensional tetrahedral mesh enrichment. Some physics of the shock wave diffraction phenomena and three-dimensional airplane flow are discussed.

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Adaptive Unstructured-Grid Computation of Shock Wave Propogation in the Gas-Particle Suspension (비정렬 적응격자를 이용한 기체-입자 혼합유체에서의 충격파 전파의 계산)

  • Park Ki-Cheol;Chang Keun-Shik
    • 한국전산유체공학회:학술대회논문집
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    • 1999.11a
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    • pp.36-41
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    • 1999
  • Shock wave propagating in the particle suspension has important applications. Examples are shock waves occurring in the solid rocket plume and detonation of dusty particles by shock waves. Experimental and numerical investigations on this subject have drawn much attention. More recently, Sivier et al. numerically simulated the experiment of Sommerfeld using the unstructured adaptive grid. They used the Eulerian-Eulerian approach based on the continuum assumption for both gas and particles. In the present paper, a new numerical method using the Lagrangian particle tracing technique and unstructured particle-adaptive grid for the polydisperse system is presented. It is explained why the existing numerical calculation has showed discrepancy with the experimental results by Sommerfeld.

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Unstructured Grid Simulations of Supersonic Mixing Using Ramp Injectors

  • Kitazume, Yoshiyuki;Miyaji, Koji
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2004.03a
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    • pp.433-439
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    • 2004
  • This paper reports the grid resolution issues on the supersonic mixing simulation inside the engine for future aerospace vehicles. Unstructured finite volume method is used for the simulations. Three types of grids are used, namely, hybrid unstructured grids composed of prism and tetrahedron cells, locally refined grids, and hexahedral grids. Hexahedral grids are used to take advantage of fine distribution naturally behind the edge of the ramp where the vortex is generated. These latter two grids show much improved evaluations of the vortex motion and the mixing of the injected and the main flows.

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Analysis of Three-dimensional Cavity flow by using Unstructred grid (비정규 격자를 이용한 3차원 Cavity 유동 해석)

  • Kang, Hyo-Kil;Kim, Moon-Chan;Chun, Ho-Hwan
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2003.10a
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    • pp.192-197
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    • 2003
  • Three-dimensional cavity flow is analyzed with the code by using unstructured grid. Incompressible Navier-Stokes equations are used as governing equations, and governing equations are discretized by Finite Volume Method. Artificial compressibility method, proposed by Chorin, and developed by Soh, is used for coupling a pressure and a velocity. Cell-centered scheme is adopted in the code, this has the effect of having denser grid than nodal scheme when the same grid is used. Weighted Averaging scheme is used for the value at a nodal point. Cavity flow is analyzed, and this computed results are compared with the results in the research report

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Development of 3-D Flow Analysis Code Using Unstructured Grid System (II) - Code's Performance Evaluation - (비정렬격자계를 사용하는 3차원 유동해석코드 개발 (II) - 코드성능평가 -)

  • Kim, Jong-Tae;Kim, Jong-Eun;Myong, Hyon-Kook
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.9 s.240
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    • pp.1057-1064
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    • 2005
  • A conservative finite-volume numerical method using unstructured meshes, which is developed by the authors, is evaluated for its application to several 2-D benchmark problems using a variety of quadrilateral, triangular and hybrid meshes. The present pressure-based numerical method for unstructured mesh clearly demonstrates the same accuracy and robustness as that fur typical structured mesh.

NUMERICAL SIMULATION OF INCOMPRESSIBLE LAMINAR ENTRY FLOWS IN A SQUARE DUCT OF $90^{\circ}$ BEND BY UNSTRUCTURED CELL-CENTERED METHOD (비정렬 셀 중심 방법에 의한 정사각형 단면을 갖는 $90^{\circ}$ 곡관 층류유동의 수치해석)

  • Myong H. K.;Kim J. E.
    • 한국전산유체공학회:학술대회논문집
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    • 2005.10a
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    • pp.81-85
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    • 2005
  • Three-dimensional steady incompressible laminar entry flows in a square duct of $90^{\circ}$ bend are numerically simulated by a new solution code(PowerCFD) using unstructured cell-centered method. Solutions are obtained with three unstructured grid types of hexahedron, prism and hybrid at a Reynolds number, based on the hydraulic diameter and bulk velocity, of 790. Interesting features of the flow are presented in detail. Detailed comparisons between the computed solutions and the available experimental data are given mainly for the velocity distributions at cross-sections in a $90^{\circ}$ bend of a square duct with fully-developed entry flows. It is found that the code is capable of producing the nature of laminar flow in curved square duct with no grid type dependency.

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Unstructured Finite-Volume Analysis of Vaporization Characteristics of Fuel Droplets in Laminar Flow Field (비정렬 유한체적법을 이용한 유동장 내의 연료액적 증발 특성 해석)

  • Kim, T.J.;Kim, Y.M.;Sohn, J.L.
    • Journal of ILASS-Korea
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    • v.5 no.1
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    • pp.13-22
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    • 2000
  • The present study has numerically analyzed the vaporization characteristics of fuel droplets in the high temperature convective flow field. The axisymmetric governing equations for mass, momentum, energy, and species are solved by an iterative and implicite unstructured finite-volume method. The moving boundary due to vaporization is handled by the deformable unstructured grid technique. The pressure-velocity coupling in the density-variable flows is treated by the SIMPLEC algorithm. In terms of the matrix solver, Bi-CGSTAB is employed for the numerically efficient and stable convergence. The n-decane is used as a liquid fuel and the initial droplet temperature is 300K. Computations are performed for the nonevaporating and evaporating droplets with the relative interphase velocity(25m/s). The unsteady vaporization process has been simulated up to the nondimensional time, 25. Numerical results indicate that the mathematical model developed in this study succesfully simulates the main features of the droplet vaporization process in the convective environment.

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