• Title/Summary/Keyword: 예조건화된 Navier-Stokes 방정식

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Temperature Preconditioning for Improving Convergence Characteristics in Calculating Low Mach Number Flows, II: Navier-Stokes Equations (저속 유동 계산의 수렴성 개선을 위한 온도예조건화 II: 나비어스톡스 방정식)

  • Lee, Sang-Hyeon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.35 no.12
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    • pp.1075-1081
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    • 2007
  • The temperature preconditioning is applied to the Navier-Stokes equations. Also, a new concept of diffusion Mach numbers is introduced to modify the reference Mach number for the Navier-Stokes equations. Flows over a circular cylinder were calculated at different Reynolds numbers. It is shown that the temperature preconditioning improves the convergence characteristics of Navier-Stokes equations. Also, it is shown that the modified reference Mach number alleviates the convergence problems at locally low speed regions.

Effects of Characteristic Condition Number on Convergence in Calculating Low Mach Number Flows, II : Navier-Stokes Equations (저속 유동 계산의 수렴성에 미치는 특성 조건수의 영향 II : 나비어스톡스 방정식)

  • Lee, Sang-Hyeon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.36 no.2
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    • pp.123-130
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    • 2008
  • The effects of characteristic condition number on the convergence of preconditioned Navier-Stokes equations were investigated. The two-dimensional preconditioned Navier-Stokes adopting Choi and Merkle's preconditioning and the temperature preconditioning are considered. Preconditioned Roe's FDS scheme was adopted for spatial discretization and preconditioned LU-SGS scheme was used for time integration. It is shown that the convergence characteristics of the Navier-Stokes equations are strongly affected by the characteristic condition number. Also it is shown that the optimal characteristic condition numbers for viscous flows are larger than that in inviscid flows.

Application of Preconditioning to Navier-Stokes Equations (예조건화 방법론의 Navier-Stokes 방정식에의 적용)

  • 이상현
    • Journal of the Korean Society of Propulsion Engineers
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    • v.8 no.1
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    • pp.16-26
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    • 2004
  • The objective of this study is to apply preconditioning to Wavier-Stokes equations with a turbulence model. The concept of a pseudo sonic speed was adopted. Roe's FDS was used for spatial discretization, LU-SGS scheme was used for time integration. In order to test the algorithms, the low speed flows around NACA airfoils and the flows through supersonic nozzle were calculated. The algorithm developed in the present study shows good performance in the calculations of low speed viscous flows and supersonics flows.

An Approach to Alleviate Cancellation Problem of Temperature Preconditioned Navier-Stokes Equations (온도예조건화 나비어스톡스 방정식의 계산오차 문제 완화 방법 연구)

  • Lee, Sang-Hyeon
    • Journal of the Korean Society of Propulsion Engineers
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    • v.14 no.1
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    • pp.11-19
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    • 2010
  • An approach to reduce cancellation errors of the temperature preconditioned Navier-Stokes equations is proposed. This approach is also applied to the conventional preconditioning methods. Adiabatic laminar viscous flows around a circular cylinder are calculated at different Mach numbers. It is shown that a redefinition of total enthalpy for reducing magnitude of the enthalpy remarkably alleviates cancellation problems of the temperature preconditioning.

Convergence Study of the Multigrid Navier-Stokes Simulation : II. Implicit Preconditioners (다중 격자 Navier-Stokes 해석을 위한 수렴 특성 연구 : II. 내재적 예조건자)

  • Kim, Yoon-Sik;Kwon, Jang-Hyuk
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.32 no.6
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    • pp.1-8
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    • 2004
  • The objective of this study is convergence acceleration of multigrid Navier-Stokes solvers. This study has been performed to enhance the performance of preconditioned multi-stage time stepping method which is a popular smoother for the multigrid Navier-Stokes solvers. Comparative study on the convergence characteristics of the ADI and DDADI preconditioners has been conducted. It is shown that the DDADI preconditioner has better performance than the ADI by numerical tests on the 2-D compressible turbulent flows past airfoils. The Spalart-Allmaras turbulent model and the Baldwin-Lomax turbulent model have been compared with the multigrid calculations.

Parallel lProcessing of Pre-conditioned Navier-Stokes Code on the Myrinet and Fast-Ethernet PC Cluster (Myrinet과 Fast-Ethernet PC Cluster에서 예조건화 Navier-Stokes코드의 병렬처리)

  • Lee, G.S.;Kim, M.H.;Choi, J.Y.;Kim, K.S.;Kim, S.L.;Jeung, I.S.
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.30 no.6
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    • pp.21-30
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    • 2002
  • A preconditioned Navier-Stokes code was parallelized by the domain decomposition technique, and the accuracy of the parallelized code was verified through a comparison with the result of a sequential code and experimental data. Parallel performance of the code was examined on a Myrinet based PC-cluster and a Fast-Ethernet system. Speed-up ratio was examined as a major performance parameter depending on the number of processor and the network communication topology. In this test, Myrinet system shows a superior parallel performance to the Fast-Ethernet system as was expected. A test for the dependency on problem size also shows that network communication speed in a crucial factor for parallel performance, and the Myrinet based PC-cluster is a plausible candidate for high performance parallel computing system.

Convergence Acceleration Methods for the Multigrid Navier-Stokes Computation (다중 격자 Wavier-Stokes 해석의 수렴성 증진 기법)

  • Kim Yoonsik;Kwon Jang Hyuk;Choi Yun Ho;Lee Seungsoo
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.35-38
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    • 2002
  • The convergence acceleration methods for the compressible Wavier-Stokes equations are studied ,which are multigrid method and implicit preconditioned multistage time stepping method. In this paper, the performance of implicit preconditioning methods are studied for the full-coarsening multigrid methods on the high Reynolds number compressible flow computations. The effect of numerical flux on the convergence are investigated for the inviscid and viscous calculations.

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Convergence Study of the Multigrid Navier-Stokes Simulation: I. Upwind Schemes (다중 격자 Navier-Stokes 해석을 위한 수렴 특성 연구 : I. 상류 차분 기법)

  • Kim, Yoon-Sik;Kwon, Jang-Hyuk
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.32 no.3
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    • pp.1-9
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    • 2004
  • This study concentrates on the upwind schemes for convergence acceleration of the multigrid method for the Navier-Stokes equations. Comparative study of the upwind schemes in the Fourier space has been performed to identify why the second-order upwind scheme with enlarged stencil can be preconditioned better than the classical second-order upwind scheme. The full-coarsening multigrid method with implicit preconditioned multistage scheme has been implemented for verification of analysis. Numerical simulations on the inviscid and turbulent flows with the Spalart-Allmaras turbulent model have been performed. The results showed consistent trend with the analysis.

Parallel Preconditioner for the Domain Decomposition Method of the Discretized Navier-Stokes Equation (이산화된 Navier-Stokes 방정식의 영역분할법을 위한 병렬 예조건화)

  • Choi, Hyoung-Gwon;Yoo, Jung-Yul;Kang, Sung-Woo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.6
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    • pp.753-765
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    • 2003
  • A finite element code for the numerical solution of the Navier-Stokes equation is parallelized by vertex-oriented domain decomposition. To accelerate the convergence of iterative solvers like conjugate gradient method, parallel block ILU, iterative block ILU, and distributed ILU methods are tested as parallel preconditioners. The effectiveness of the algorithms has been investigated when P1P1 finite element discretization is used for the parallel solution of the Navier-Stokes equation. Two-dimensional and three-dimensional Laplace equations are calculated to estimate the speedup of the preconditioners. Calculation domain is partitioned by one- and multi-dimensional partitioning methods in structured grid and by METIS library in unstructured grid. For the domain-decomposed parallel computation of the Navier-Stokes equation, we have solved three-dimensional lid-driven cavity and natural convection problems in a cube as benchmark problems using a parallelized fractional 4-step finite element method. The speedup for each parallel preconditioning method is to be compared using upto 64 processors.

Application of A Local Preconditioning Method for 3-D Compressible Low Mach Number Flows (3차원 저속 압축성 유동 해석을 위한 국소 예조건화 기법 적용 연구)

  • Yoo, Il-Yong;Jin, Min-Suk;Kwak, Ein-Keun;Lee, Seung-Soo
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.36 no.10
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    • pp.939-946
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    • 2008
  • Euler codes or Navier-Stokes codes for compressible flows suffer severe degradation in convergence as Mach number approaches zero. The convergence problem arose from the wide disparity in characteristic speeds can be solved using preconditioning methods without large modifications. In this paper, a preconditioned RANS(Reynolds Averaged Navier-Stokes) solver is developed for analysis of low Mach number flows. In order to validate the method, computational examples are chosen and the results are compared with the experimental data and the existing computed results showing a good accuracy and convergence characteristics for steady inviscid, laminar and turbulent flows at low Mach number.