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Adaptive grid generation for 3D unstructured grids
KTH, School of Engineering Sciences (SCI), Mechanics.
(English)Manuscript (preprint) (Other academic)
National Category
Fluid Mechanics and Acoustics
URN: urn:nbn:se:kth:diva-24076OAI: diva2:343227
QC 20100812Available from: 2010-08-12 Created: 2010-08-12 Last updated: 2010-08-12Bibliographically approved
In thesis
1. Hybrid Grid Generation for Viscous Flow Computations Around Complex Geometries
Open this publication in new window or tab >>Hybrid Grid Generation for Viscous Flow Computations Around Complex Geometries
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A set of algorithms building a program package for the generation of twoandthree-dimensional unstructured/hybrid grids around complex geometrieshas been developed.

The unstructured part of the grid generator is based on the advancing frontalgorithm. Tetrahedra of variable size, as well as directionally stretched tetrahedracan be generated by specification of a proper background grid, initiallygenerated by a Delaunay algorithm.

A marching layer prismatic grid generation algorithm has been developedfor the generation of grids for viscous flows. The algorithm is able to handleregions of narrow gaps, as well as concave regions. The body surface is describedby a triangular unstructured surface grid. The subsequent grid layers in theprismatic grid are marched away from the body by an algebraic procedurecombined with an optimization procedure, resulting in a semi-structured gridof prismatic cells.

Adaptive computations using remeshing have been done with use of a gradientsensor. Several key-variables can be monitored simultaneously. The sensorindicates that only the key-variables with the largest gradients give a substantialcontribution to the sensor. The sensor gives directionally stretched grids.

An algorithm for the surface definition of curved surfaces using a biharmonicequation has been developed. This representation of the surface canbe used both for projection of the new surface nodes in h-refinement, and theinitial generation of the surface grid.

For unsteady flows an algorithm has been developed for the deformationof hybrid grids, based on the solution of the biharmonic equation for the deformationfield. The main advantage of the grid deformation algorithm is that itcan handle large deformations. It also produces a smooth deformation distributionfor cells which are very skewed or stretched. This is necessary in orderto handle the very thin cells in the prismatic layers.

The algorithms have been applied to complex three-dimensional geometries,and the influence of the grid quality on the accuracy for a finite volumeflow solver has been studied for some simpler generic geometries.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. viii, 48 p.
Trita-MEK, ISSN 0348-467X ; 2009:17
grid generation, unstructured grids, hybrid grids, surface grids, three-dimensional grids, adaptive grids, moving grids, grid quality, accuracy
National Category
Fluid Mechanics and Acoustics
urn:nbn:se:kth:diva-11934 (URN)978-91-7415-491-7 (ISBN)
Public defence
2010-02-19, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:15 (English)
QC 20100812Available from: 2010-01-27 Created: 2010-01-27 Last updated: 2010-08-12Bibliographically approved

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