THE APPLICATIONS OF AN UNSTRUCTURED GRID BASEDOVERSET GRID SCHEME TO APPLIED AERODYNAMICS

THE APPLICATIONS OF AN UNSTRUCTURED GRID BASED

OVERSET GRID SCHEME TO APPLIED AERODYNAMICS

Thomas C. Wey ∗

Hernandez Engineering Inc. Houston, TX. U.S.A. wey@

ABSTRACT

The traditional structured grid based chimera grid scheme is extended to include the unstructured hexahedrons as the component grids. Recent developments of a quadrilateral based radiated grid (also known as hair grid) and a hexahedral based tree grid generators are described. The main input method for the quadrilateral dominated sur-face mesh generator is through IGES files from most CAD packages. Example is given for X-38, a crew return spacecraft designed by JSC/NASA.

Keywords: mesh generation, chimera, overset, quadrilateral, hexahedral, IGES, tree grid.

∗

Specialist II.

Copyright © 1999 by Hernandez Engineering, Inc. Published by 8th International Meshing Roundtable with permission. In ac-cordance with Public Law 96-517, the Author has elected to retain tile to this Paper. Inquiries concerning rights for its commer-cial use should be addressed to: Hernandez Engineering, Inc., ATTN: Legal Office, 17625 El Camino Real, Suite 200, Houston,Texas 77058.

1. INTRODUCTION

Overset grid techniques allow each component or partition of a given configuration to be gridded independently and superimposed to form a composite of overset meshes for partial differential equations 1. Because each meshes are generated independently, some mesh points lie within another body boundary and these points are ‘cut out’leaving holes in the mesh. Such hole points and pointers used to update overset mesh boundaries are automatically located with available software 2 3. To resolve the viscous boundary layer, CFD simulations require extremely fine grid spacing in the direction `normal’ to the body surface and practical issues dictate that the solution algorithm be implicit in this direction. Along the body surface and away from the body the grid spacing requirements are much reduced. Since it is only necessary to radiate a grid a short

distance away from the body to a rather modest back-ground mesh that covers the field, one might simply grid a body with multiple structured component grids. As the configurations to be analyzed become more complex, the time required to grid the entire body even with multiple structured grids is increased dramatically. It remains a time consuming task and requires some user expertise and significant effort. The automatic surface domain creation is becoming one of emerging topics in the surface mesh generation. One approach developed by Chan and Gomez 4implemented an automatic seam curve and corner identifi-cation scheme and a spider web grid generation method to complete the seam grid generation and achieve the auto-mation for certain classes of geometry. Depending on the nature of topology of the grids, the interface of volume meshes between component grids are still time consuming tasks. Even the automatic overset volume mesh interface programs, such as OVERGC (see Reference 3) and PEG-