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Parameter Investigation with Line-Implicit Lower-Upper Symmetric Gauss-Seidel on 3D Stretched Grids
2014 (English)Conference paper, Published paper (Refereed)
Abstract [en]

An implicit Lower-Upper Symmetric Gauss-Seidel (LU-SGS) solver has been implemented as a multigrid smoother combined with a line-implicit methodas an acceleration technique for Reynolds-Averaged Navier-Stokes (RANS) simulation on stretched meshes.The Computational Fluid Dynamics code concerned is Edge, an edge-based finite volume Navier-Stokesflow solver for structured and unstructured grids.The paper focuses on the investigation of the parameters related to our novel line-implicit LU-SGSsolver for convergence acceleration on 3D RANS meshes. The LU-SGS parameters are defined as the Courant-Friedrichs-Lewy number, the Left Hand Side dissipation,and the convergence of iterative solution of the linear problem arising from the linearisation of the implicit scheme.The influence of these parameters on the overall convergence is presented and default values are defined formaximum convergence acceleration. The optimized settings are applied to 3D RANScomputations for comparison with explicit and line-implicit Runge-Kutta smoothing. For most of the cases, a computing time acceleration of the order of 2 is found depending on the mesh type, namely the boundary layer and the magnitude of residual reduction.

Place, publisher, year, edition, pages
2014.
National Category
Aerospace Engineering
Identifiers
URN: urn:nbn:se:kth:diva-156411OAI: oai:DiVA.org:kth-156411DiVA: diva2:766615
Conference
AIAA AVIATION 2014 - 44th AIAA Fluid Dynamics Conference
Note

QC 20141201

Available from: 2014-11-27 Created: 2014-11-27 Last updated: 2014-12-01Bibliographically approved
In thesis
1. Acceleration of Compressible Flow Simulations with Edge Using  Implicit Time Stepping
Open this publication in new window or tab >>Acceleration of Compressible Flow Simulations with Edge Using  Implicit Time Stepping
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Computational fluid dynamics (CFD) is a significant tool routinely used indesign and optimization in aerospace industry. Often cases with unsteadyflows must be computed, and the long compute times of standard methods hasmotivated the present work on new implicit methods to replace the standardexplicit schemes. The implementation and numerical experiments were donewith the Swedish national flow solver Edge, developed by FOI,universities, and collaboration partners.The work is concentrated on a Lower-Upper Symmetric Gauss-Seidel (LU-SGS)type of time stepping. For the very anisotropic grids needed forReynolds-Averaged Navier-Stokes (RANS) computations of turbulent boundary layers,LU-SGS is combined with a line-implicit technique.  The inviscid flux Jacobians which contribute to the diagonalblocks of the system matrix are based on a flux splitting method with upwind type dissipation giving  control over diagonal dominance and artificial dissipation.The method is  controlled by several parameters, and comprehensivenumerical experiments were carried out to identify their influence andinteraction so that close to optimal values can be suggested. As an example,the optimal number of iterations carried out in a time-step increases with increased resolution of the computational grid.The numbering of the unknowns is important, and the numberings produced by mesh generators of Delaunay- and advancing front-type wereamong the best.The solver has been parallelized with the Message Passing Interface (MPI) for runs on multi-processor hardware,and its performance scales with the number of processors at least asefficiently as the explicit methods. The new method saves typicallybetween 50 and 80 percent of the runtime, depending on the case, andthe largest computations have reached 110M grid nodes. Theclassical multigrid acceleration for 3D RANS simulations was foundineffective in the cases tested in combination with the LU-SGS solverusing optimal parameters. Finally, preliminary time-accurate simulations for unsteady flows have shown promising results.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xv, 97 p.
Series
TRITA-AVE, ISSN 1651-7660 ; 2014:72
Keyword
Compressible CFD, Convergence Acceleration, Implicit Time-Stepping, LU-SGS, Upwind Type Dissipation, Line-implicit, Ordering, Parallelization, Parameters, Multigrid
National Category
Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-156414 (URN)978-91-7595-370-0 (ISBN)
Public defence
2014-12-12, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20141201

Available from: 2014-12-01 Created: 2014-11-27 Last updated: 2014-12-01Bibliographically approved

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Otero, Evelyn

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