Doctoral defense
Hybrid grid generation for viscous flow computations around complex geometries
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| Defendant |
Main Advisor |
Extra Advisor |
Date |
| Lars Tysell |
Laszlo Fuchs |
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2010-02-19 |
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| Opponent |
| Nigel Weatherill, University of Birmingham, UK
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| Evaluation committee |
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AbstractA set of algorithms building a program package for the generation of two- and three-dimensional unstructured/hybrid grids around complex geometries has been developed. The unstructured part of the grid generator is based on the advancing front algorithm. Tetrahedra of variable size, as well as directionally stretched tetrahedra can be generated by specification of a proper background grid, initially generated by a Delaunay algorithm. A marching layer prismatic grid generation algorithm has been developed for the generation of grids for viscous flows. The algorithm is able to handle regions of narrow gaps, as well as concave regions. The body surface is described by a triangular unstructured surface grid. The subsequent grid layers in the prismatic grid are marched away from the body by an algebraic procedure combined with an optimization procedure, resulting in a semi-structured grid of prismatic cells. Adaptive computations using remeshing have been done with use of a gradient sensor. Several key-variables can be monitored simultaneously. The sensor indicates that only the key-variables with the largest gradients give a substantial contribution to the sensor. The sensor gives directionally stretched grids. An algorithm for the surface definition of curved surfaces using a biharmonic equation has been developed. This representation of the surface can be used both for projection of the new surface nodes in h-refinement, and the initial generation of the surface grid. For unsteady flows an algorithm has been developed for the deformation of hybrid grids, based on the solution of the biharmonic equation for the deformation field. The main advantage of the grid deformation algorithm is that it can handle large deformations. It also produces a smooth deformation distribution for cells which are very skewed or stretched. This is necessary in order to 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 volume flow solver has been studied for some simpler generic geometries.
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