1. 12 th International Meshing Roundtable Panel Discussion Darby Vicker darby.vicker@nasa.gov 281-483-6107 September 16, 2003

2. 2 Background NASA/JSC/EG3 – Applied Aeroscience and Computational Fluid Dynamics (CFD) Branch Typical uses of CFD in our branch include –Aero databases – stability and trajectory analysis –Calibration of flight instruments – X-38 FADS –Separation models – X-38/B-52 –Verification of engineering analysis –Complete flow fields for debris analysis and flow feature extraction SSLV – Reynaldo GomezX-38/B-52 – James GreathouseHigh Fidelity X-38– Darby Vicker X-38 FADS

3. 3 CFD Tools in EG3 Two primary codes –OVERFLOW – Navier-Stokes solver Requires chimera overset structured volume grids –CART3D – Euler solver Requires triangulated surface grids (geometry definition only) Automatic volume grids via sub-divided Cartesian grids Automation is important –CFD is becoming more accepted and relied upon as an analysis tool –The frequency and number of requested solutions is increasing EG3 has been asked to produce 150+ SSLV CFD solutions on a 33 million grid-point system for one of the return-to-flight tasks –Makes automation of the complete CFD process, including grid generation, essential SSLV elevon and body flap automation – animationanimation

4. 4 Chimera Grid Generation Structured grids that arbitrarily overlap Quick turn around from grid generation to solutions –Possible to grid complex geometry with structured grids in a relatively short time –Flow solvers available are very efficient SSLV External Tank & Solid Rocket Boosters

5. 5 CAD Getting a quality representation of geometry ready for grid generation is not trivial –We receive geometry from many CAD platforms (ProEngineer, CATIA, Unigraphics, etc.) –For complex geometry, there are often undesirable “features” Slivers, gaps, highly warped or twisted surfaces, etc. Currently we rely on 3 rd party software to fix geometry problems and (usually) translate to a neutral format

6. 6 Mesh Quality Triangulated grid in high curvature –Wing leading edge example

7. 7 Desirable Software Features Batch mode operation Easily accessible feature information –Vertex location, arc length, surface area, etc. Grid diagnostics –Tabulated numbers and graphical indication of open edges, non- manifold edges, etc. Improved (structured) surface grid creation via extrusion –Ease of use –Robustness –Variety of boundary conditions Basic: float; periodic; splay; constant X, Y or Z Advanced: Follow u or v of CAD patch; follow a curve; follow exact points on a curve;