Viewgraphs on 3-dimensional Euler solutions using automated Cartesian grid generation are presented. Topics covered include: computational fluid dynamics (CFD) and the design cycle; Cartesian grid strategy; structured body fit; grid generation; prolate spheroid; and ONERA M6 wing

Berger, Marsha J.

Enomoto, Francis Y.

Melton, John E.

English

NASA Technical Reports Server

N94:22367
3D EULER SOLUTIONS USING
AUTOMATED CARTESIAN GRID
GENERATION
JOHN E. MELTON
NASA AMES RESEARCH CENTER
FRANCIS Y. ENOMOTO
NASA AMES RESEARCH CENTER
MARSHA J. BERGER
NEW YORK UNIVERSITY
PNieEDtNg PAGE BLA;'_K NOT FtLME[,
251
https://ntrs.nasa.gov/search.jsp?R=19940017894 2020-06-16T18:22:24+00:00Z
Aqenda
• History
• Cartesian Overview
• Technique Comparisons
• 3D Cartesian Grid Generation Strategy
• Survey of simple test cases
• Current research and future plans
• Summary
History
• Lessons from ATP grid generation
• AIAA 91-0637 with Thomas and Cappuccio
- Unstructured, refined, hexahedral body-fitted grid
- Euler FV RK4 Jameson flow solver algorithm (FLO57)
• TIGER = Iopologically I_ndependent, _E_EulerRefinement
• GIRAFFE = Grid I_nteractive Refinement and
Flow Eield Examination
252
CFD and the Desian Cycle
Compute better solutions faster and cheaper
Analysis Issues
Resolution adequate for detailed design
- refinement appropriate for each Mach, a, 13
Flexibility Geomet_ Issues
- Multi-block
- Unstructured
i
I_Turnaro n ,ns,,ethe0esi nc c'eiUse of CAD/CAM and automated
geometry handling wherever possible
253
Three !moortant Questions
Are CFDers doomed to eternal grid generation?
Why shouldn't CFD be like structural FEA?
I How can we automate the geometry manipulationand grid generation processes? I
(_artesian Grid Strategy
• South, Clarke, Salas, Hassan, Berger, LeVeque,
Powell, Epstein, Morinishi, TRANAIR
• Make the computer do the work
- Interactivity _ Automation
- Divorce surface grid from field grid
- Use computational geometry algorithms
to extract surface/cell intersection information
- Use NURBs (Non-Uniform Rational B-Splines)
to maintain a single, accurate, database
• Use grid refinement for "efficient" resolution
- Unstructured grid (block or cell)
- Flowfield and geometry-based refinement
254
_Task
Grid generation
Flux and BCs
Connectivity
overhead
Grid refinement/
adaptation
Flow solver
Techniaue Comparisons
Structured Body-fitted
tedious and boring
time-consuming
requires surface grid
good tools are available
Cartesian
automated
NURB accuracy
no surface grid
research software
"simple" and familiar "complicated"
minimal
-60 words/cell
not automated
difficult
automated for both
geometry and flowfield
highly vectorizable vectorizable
TIGER Surface GeomQtry
Triangles
NURBS
Advantages
"Simple" intersections
LaWGS / FEM / PANAIR
Compute -inexpensive
Direct from CAD
Complete accuracy
Complete information
NASNIGES standard
Disadvantages
Poor refinement accuracy
Creation
Loss of surface information
"Nonlinear" intersections
- tolerance specifications
- polynomial root-finding
Topology determination
Unfamiliarity
Compute - expensive
2_
2-Step Cartesian Grid Generation Alqorithm
1 - Create initial equi-spaced Cartesian grid
F Flag cells that intersect with surfaceRefine along with a number of neighbors
Repeat to create desired resolution
2 - Compute cell geometric information
• face areas
• body surface normals
• cell volumes
• face and volume centroids
Gqrrent TIGER Connectivity Data Structure
Item
Pointer to connecting cells
Face BC flags
Face area vectors
Cell Refinement Level
Cell BC flag
Cell volumes
Words per cell
6 faces x 4 connections per face
6 faces x 2 flags per face
7 faces x 3 components per face
1
1
1
Unstructured Cartesian Overhead - 60+ words per cell
256
Survey of Test Cases
• Prolate Spheroid - NURB input
• ONERA M6 wing - Triangle input
• HSCT with LE flap - Triangle input
CarteSian TIGER -i_
257
ONERA M6 Mach=0.84 _=3.06
-15 I l I 1 I I , I I
1.L£..-L [ J • J.,_65% i
I:.. ,_,,,'@-"ff_'":_'-" 1:_"_',;',_,,.,,_ I
1i: I I1_Data, It I I I I
0 0,1 02 03 0.4 05 0+6 07 0.8 09 1
WC
-' _l= 90
"..
0 ' ' " "*"'*,.._,..--;;
o,_-ri i i i i [ i. t..:.!
,i:l II1l II
0 0.1 02 03 0.4 0.5 0.6 0.7 0.8 0.9 I
x/c
-15
cp ol,,..!,...<,."_f",t..-
0.5 _ L , ° °'%'°'
,,. II
0 01 02 03 04 _006 07 08 09 1
-_s --I I I I I
-°._..._q!.: _+.Cp ... _1""': '';'j._ : _.k°._._ ... _--
0.5 "
0 0.1 0.2 0.3 04 03 06 07 08 09 1
x/c
258
HSCT Grid Generation Command Files
Step 1
1 1 use tiger.net data 2: use tiger.tri
1 1 flip y-z O: don't flip
1 1 make new base grid 2: restart
-1 4000 x-range
-1300 1700 y-range
0 1201
17 15
1
6
2
1
1
z-range
dims
1: split surface cells O: stop
: number of splitting passes
: number of buffer layers
1: reset symmetry plane cells O: skip
1: compress the files O: skip
Step 2
1 read from tiger.net 2: tiger.tri
1 flip y-z O: don't flip
1 reset symmetry plane cells O: skip
1: compress files O: skip
\
259
Current Research and Future Plan-_
• Improved flux and dissipation modeling
• Improved boundary conditions
• "Intelligent" grid generation
• Flowfield refinements
• Validations
Summary
• Use of a single NURB geometry database for design and analysis has
many advantages
- allows for geometry manipulation with commercial CAD/CAM tools
provides analyst with complete and accurate surface information
- provides consistent method for data transfer
• A mature unstructured Cartesian approach will have additional advantages
- eliminate surface and volume gridding tasks via automation
- provide local resolution appropriate for each flow condition
- shrink CFD turnaround from months to hours
- allow designers to concentrate on aerodynamic performance instead of
computational geometry and numerical analysis
• Interactive techniques should be viewed as short term solutions, and not
as long term CFD goals
260


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