Cartesian Mesh Simulations for Complex Geometry

Technical Summary Author: Capt. Michael J. Aftosmis, USAF/NASA

Co-investigators: John. E. Melton, Code AAC, NASA Ames

Research Objective

To understand the near-field aerodynamics of an advanced high wing transport aircraft.

Approach

This project was approached as an application of an existing Cartesian mesh package for solving the Euler equations around arbitrary geometries. The Cartesian approach uses a non-body fitted Cartesian hexagons which are permitted to intersect the geometry and leave irregularly shaped cells at the body surface. Successive subdivision of mesh cells is used to automatically resolve both flow gradients and small geometric features. This specific project was conducted part of an effort in advanced development of the Cartesian mesh method, and focused on automation of the adaptation scheme over many flow solve/adapt cycles.

Accomplishment Description

The first figure shows a front 3/4 view of an advanced transport in an approach configuration with high-lift devices deployed. The geometry consisted of 18 separate (but intersecting) components. These components were described by surface triangulations containing 700,000 vertices. The adaptive Cartesian volume mesh sown in the second figure contained 1.65M cells at 9 levels of refinement thus providing resolution to about 1/2 inch on the scale of the actual geometry. The stream-ribbons shown in the third figure provide a view of a typical discrete solution for this configuration. This example required a maximum of 256Mw of memory and was arrived at without user intervention after the original specification of the geometry.

Significance

The rapid turnaround afforded by the Cartesian approach permitted timely analysis of the flow near the rear of the aircraft as part of a larger government and contract effort aimed at adopting a safe egress strategy for the aircraft.

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Future Plans

The surface modeling, mesh generation and flow solver are currently undergoing significant revision to improve their utility, decrease memory requirements and improve computational efficiency. The new "Cart3d" Cartesian mesh system will be complete sometime during the '96 NAS year. The package is aimed not only at the HWT project discussed here, but at a variety of projects which involve 3D flow around realistically complex configurations.

Publications

Aftosmis, M.J., Melton, J.E., and Berger, M.J., "Adaptation and Surface Modeling for Cartesian Mesh Methods." AIAA Paper 95-1725-CP, Jun. 1995.

Aftosmis, M.J., "Emerging CFD Technologies and Aerospace Vehicle Design," Proceedings of the NASA Workshop on Surface Modeling, Grid Generation and Related Issues, NASA Lewis Rsch Cntr, NASA CP 3291, May 1995.

Melton, J.E., Berger, M.J., Aftosmis, M.J., and Wong M.D.,"Development and Application of a 3D Cartesian Grid Euler Method"Proceedings of the NASA Workshop on Surface Modeling, Grid Generation and Related Issues, NASA Lewis Rsch Cntr, NASA CP 3291, May 1995.

Schreck, S.J., "Use of Computational Fluid Dynamics Optimizes C-17 Paratroop Deployment," AFOSR Research Highlights, May 1995. Air Force Off. of Sci. Rsch., Bolling AFB, DC 20332.