A grid generation procedure combining interactive and batch grid generation programs was put together to generate multi-block grids for complex aircraft configurations. The interactive section provides the tools for 3D geometry manipulation, surface grid extraction, boundary domain construction for 3D volume grid generation, and block-block relationships and boundary conditions for flow solvers. The procedure improves the flexibility and quality of grid generation to meet the design/analysis requirements

Appleby, Ruth

Kao, T. J.

Su, T. Y.

English

NASA Technical Reports Server

N92-244t9
AN INTERACTIVE MULTI-BLOCK GRID GENERATION SYSTEM
T. J. Kao and T. Y. Su
Aerodynamics Research, Engineering Division
Boeing Commercial Airplane Group
Seattle, WA
Ruth Appleby
CFD Computing
Boeing Computer Services
Seattle, WA
SUMMARY
A grid generation procedure combining interactive and batch grid generation programs has been put
together to generate multi-block grids for complex aircraft configurations. The interactive section provides
the tools for 3D geometry manipulation, surface grid extraction, boundary domain construction for 3D
volume grid generation, and block-block relationships and boundary conditions for flow solvers. The
procedure improves the flexibility and quality of grid generation to meet the design/analysis requirements.
INTRODUCTION
The process for conducting a computational fluid dynamics (CFD) analysis usually follows four steps:
• Geometry modeling
• Model discretization (2D and 3D)
• Flow analysis
• Result interpretation.
As the flow codes become more reliable and easy to use, the flowtime for acquiring a solution becomes
relatively small when compared to the pre-processing step of geometry modeling and discretization, the
most difficult and time-consuming aspects of the process.
This paper describes a multiblock grid generation approach in which geometry continuity is maintained
and the required surface grids and block definition are prepared using the Boeing-developed Aero Grid and
Paneling System (AGPS)[ 1,2 ], and the block-block relationship bookkeeping and boundary conditions
are achieved using an interactive graphics interface program, BCON[3].
A unique feature of AGPS is that it is a geometry programming language. It allows users to create
command files to perform specific tasks. This has allowed us to develop a collection of command files
specifically for grid generation problems. This grid generation package contains geometry manipulation
tools, various gridding functions, and graphics utilities for generating surface grids and defining block
topology. And most importantly, the surface grids in AGPS are based on the actual mathematical
surfaces, not approximations.
BCON is a menu-driven graphics interface program. BCON input consists of strings.or arrays of
points generated from AGPS or another CAD tool/surface geometry source. It generates input files that
contain the block definitions, the block relationships and the block boundary conditions required for a
multi-block volume grid generation and flow solver.
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The combination of AGPS and BCON provides an effective means of producing surface and field
grids for arbitrary three-dimensional configuration. In the following sections, we discuss some of the
results in applying current procedures.
METHOD/APPROACH
The current approach is to use AGPS to define lines, curves, and surfaces at the block or sub-block
boundaries and then to extract the edge and surface grids on these lines, curves, and surfaces. After the
edge and surface grids are defined, BCON interactively combines those edge and surface grids into
blocks, then writes out block data for 3D volume grid generation and block-block relationships with
boundary conditions for an Euler or Navier-Stokes flow solver [4]. We are currently generating 3D
volume grids with the Eglin Arbitrary Geometry implicit Euler (EAGLE), a batch-oriented
algebraic/elliptical grid code[5]. Figure 1 shows the relationships of each step. It should be noted that this
approach is not limited to a particular 3D grid code.
AGPS CAPABILITY
A 3D surface geometry system, AGPS was designed by aerodynamicists primarily for aerodynamics
applications. AGPS is a useful tool during the preprocessing and postprocessing steps of the CFD
process because of its ability to model both general and complex geometric shapes. It allows for double-
valued curves and surfaces and has a variety of surface and curve types, including bicubic, biquintic,
conic, interpolated, non-uniform rational B-spline (NURBS), and ruled. It generates surface intersections
easily and accurately and has a unique subrange surface capability that allows surfaces to be broken or
trimmed into smaller regions while keeping the exact mathematical definition used in the original. AGPS-
generated surface lofts can be checked thoroughly for flaws using shaded graphics, curvature plots, and
various other methods, helping the user achieve a surface with the desired characteristics.
Most importantly, AGPS is more like a geometry programming language than a program itself. The
command files make it easy to repeat tasks. In addition, a playback feature is available to interactively
record the steps followed.
With the AGPS user-accessible menu (Figure 2) and command file smactures, we have developed a
grid generation package that includes data I/O, geometry manipulation, various gridding functions, and
graphics utilities. Inexperienced users need only limited CAD or geometry training and do not need to
understand internal data smacture or remember a multitude of object names during the operations. With
some experience, users can tailor the package to fit their particular needs.
Currently, the primary function of the grid generation package is to define block edges and faces for a
multiblock structured grid. As shown in Figure 2, the package allows users to
1. Input AGPS geometry and extracted grids
2. Manipulate curve and surface geometry
3. Extract curve and surface grids
4. Output grids in a specified format
5. Manipulate graphics displays and a geometry database
These functions give engineers a set of highly interactive graphics tools in a single environment to generate
geometry, distribute points, and interface with a particular 3D grid generator and/or flow solver.
After preparing the block layout topology, including the number blocks, shape and size of each block,
and location of the blocks, the user then creates the block layout interactively by defining lines,curves,
and surfaces at the block and sub-block boundaries. Next, the edge and surface grids are generated. The
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pointsareextracteddirectly from thecurvesandsurfacesandlie preciselyon theoriginal mathematical
definitions.Theusercanalsocontrolgriddistributionandperformgrid manipulations uchasmergingand
splitting.
BCONCAPABILITY
BCONis amenu/mouse-driven,interactivegraphicsinterfaceprogramwrittenin C andusingNASA-
AmesResearchCenter'sPANELLibrary for a graphicaluserinterfaceon theSiliconGraphicsInc.'sIRIS
graphicsworkstations.Theuserfirst preparesthegeometrysurfacedefinitionanddecideson theblock
topology,aswell assurfacegrids,with AGPS. With BCON,theuserthendefinesblocks,block-block
relationships,andboundaryconditionsfor input to thevolumegrid code(currently,EAGLE) andtheflow
solver. BCONacceptsinputin theform of stringsor arraysof pointsfrom AGPSor other
geometry/surfacegrid generationsources.It is highlymodular,whichallowsnewfeaturesto be
incorporatedeasily.
MajorfunctionsBCONprovidesare
1. Input
2. Defineblock
3. Define i, j, k indexsystemfor eachblock
4. Imposeboundaryconditions
5. Write EAGLErunstreamandinputdatadeck
6. Write block-blockrelationshipandboundaryconditionsinput files for flow solvers
To simplify thedatapreparationandreduceredundantdata,uniqneedge/faceis requiredandeach
block shouldberepresentedbyasmanyedges/sub-edgesa possible.In casesof original geometry,or
whenit is necessaryto preservethedistributionof interfacepoints,blocksarerepresentedby
faces/subfaces.Onceafaceis defined,noedgeassociatedwith thatfaceneedsto beprepared;BCON
codecanidentify theedgefrom therelatedface.
Eachblockcanbeformedbyacombinationof edges/sub-edgesandfaces/sub-faces.Fora simpleface,
only two edgesneedto bedefined.For asimpleblock,only twooppositefacesneedto bedefined. If a
block hascomplexfaces,thesefacesneedto bedefinedf'u'st.Similarly, if a facehascomplexedges,the
edgesneedto bedefinedfirst. BCONpicksup theremainingsimpleedges/facesautomaticallyandforms
theblock.
BCONletstheuserinteractivelyselectheorigin fromoneof theblockverticesanddefinethe
directionsof the local indicesi, j, andk for thefirst block. Thecodewill propagatetheseindices
throughoutall theblocksdef'medin theblockingprocess.Theblock-blockrelationshipis established
duringthisprocess.Oncetheblockingprocessis finished,only thefaceswithoutneighborblocksare
displayed;on thesefaces,theusercanimposea varietyof boundaryconditions,i.e. solid wall, symmetry
plane,inlet, exhaust,andfar-field. Outputfiles includetheEAGLE runstreamandinputdatadeckfor 3D
volumegrid generation,aswell asblock-blockrelationshipsandboundaryconditioninputfiles for flow
solvers.
APPLICATIONS
To demonstratethecapabilityof thepresentprocedure,wehavestudiedseveraltestcases,from simple
twoblockswing/bodyto full configurationfour-enginetransportairplane. Figure3 showsthesurface
gridof awing/nacelle/strutconfiguration.Thecompleteflow field consistsof 20blocks(Figure4) with a
totalnumberof 60,000grid points. An H-typegrid is usedfor all externalflow field, andacylindrical
grid is usedfor nacelleinlet andexhaustflow. Figure5 showstheisobarsof Euleranalysison the
configurationsurfaces.
Figure6 showssurfacegridsfor thebody/wing/strut/nacelletwin-enginetransportmodel. The
volumegrid containedapproximately1.2million grid pointsandwascomposedof 26 to 32blocks,
335
depending on the nacelle simulation. The entire flow through nacelle configuration (with pylon, wing, and
fuselage) is modelled with 32 blocks (Figure 7). Fifteen of these blocks are used for the flow-through
core and fan cowls. Figure 8 shows constant K plane field grid with part of the surface grid of a fan cowl.
Figure 9 shows a comparison of computed wing Cp with wing tunnel data for nacelle installed at
eta=0.34, at M=0.77 with C1=0.55.
The third case is the high speed civil transport (HSCT). Figures 10 shows a symmetry plane and
surface grid for cruise configuration with vertical tail. Figure 11 shows the surface grids for high-lift
configuration without a vertical tail. The general block layout for high-lift and cruise configuration is
shown in Figure 12. It used 10 blocks for a cruise case and 18 blocks for a high-lift case. Figure 13
shows the surface streamlines for both cruise and high-lift cases.
The last case is a four-engine 747-200 full configuration for Navier-Stokes analysis. The complete
flow field consists of approximately 45 blocks with over 2 million grid points. Figure 14 shows the
complete geometry surface grids. Figure 15 shows a layout of some blocks near the configuration. For
this case, the viscous calculation was limited to the wing. It took 14 blocks to cover the boundary layer
region. Figure 16 shows viscous blocks near a wing/body junction.
CONCLUSION
The combination of the AGPS Grid Generation Package and the BCON program significantly reduces
the flowtime required for generating and pre-processing 3D multiblock grids. The long term goal of this
effort is to merge these two capabilities with 3D volume grid generation into one integrated environment,
giving users timely, accurate 3D grid generation.
REFERENCES:
.
.
.
.
D.K.Snapp and R. C. Pomeroy, "A Geometry System for Aerodynamic Design," AIAA/AHS/ASEE
Aircraft Design, System, and Operations Meeting, AIAA-87-2902, September 14-16, 1987.
W. K. Capron and K. L. Smit, "Advanced Aerodynamic Applications of an Interactive Geometry and
Visualization System," 29th Aerospace Sciences Meeting, AIAA-91-0800, January 7-10, 1991.
T. Y. Su, R. A. Appleby, and H. C. Chen, A General Multiblock Euler Code for Propulsion
Integration, Volume H: User Guide for BCON, Preprocessor for Grid Generation and GMBE, NASA
CR187484, May 1991.
N. J. Yu, H. C. Chen, T. Y. Su, and T. J. Kao, "Development of a General Multiblock Flow Solver
for Complex Configuration," Proceedings of the Eighth GAMM Conference on Numerical Methods in
Fluid Mechanics, 1990.
5. J.F. Thompson, Program EAGLE User's Manual, AFATL-TR-88-117, Vol. III, September, 1988.
336
AGPS
Geometry definition/manipulation
Block layout
Edge/surface grid
BCON
Block-block relationship
Boundary condition
EAGLE
field grid
FLOW SOLVER
Navier-Stokes
Figure 1. Multiblock grid generation process.
I AGPS DEFAULT MENU J
TASK MENUS I
GRID GENERATION I
•--[ GEOMETRY INPUT
"--[CREATE LINFJCURVE
•-_ CREATE SURFACE
•-.( DEFINE EDGE
-[DEFINE FACE
--{ OUTPUT GRIDS
--[ UTILITIES
Figure 2. AGPS user-accessible menu.
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Figure 3. Surface grids for a wing/nacelle/strut.
338
Figure 4. Bl_)ckslayout for a wing/nacelle/strut.
Figure 5. Isobar for a wing/nacelle/strut configuration
at Mach=0.8, Alpha=2.0.
Figure 6. Surface grids for a body/wing/nacelle/strut.
339
I_" _ _ _-_ \_.\
\
Figure 7. Blocks layout for a body/wing/nacelle/strut.
Figure 8. Constant K-plane field grid with fan cowl surface grids.
340
Cp
-15
-I .0
-0.5
0.0 -
0.5- 0
1.0 I
-0.1
I I I I I I I I I I I
0.1 0.3 0.5 0.7 0.9 I.!
X/C
(a)
Cp
-1.5 -
-1.0 -
-0.5 -
0.0-
0.5-
1.0
-0.1
- GMBE 1] = 0.277
00o o EXIrF T] = 0.277
°o2_° o _° °o'_'-.
W. o 2oo',,,"
I I I I I I I I I I I
0.1 0.3 0.5 0.7 0.9 1.1
X/C
(b)
Cp
-1.5
-I .0 -
-0.5
0.0 ¸
0.5-
1.0
-0,1
Lower surface orifices only
- GMBE rI = 0.310
o EXIT 1] = 0.310
o o
I I I I I I I I I I I I
0.1 0.3 0.5 0.7 0.9 1.1
X/C
(C)
Cp
-!.5 _ Lower surface orifices only
-1.0q - GMBE rl = 0.371
A o EXIrF q = 0.375
I
-0.5 -"
0.0
0.5_
-lo
1.0 I I I I 1 I I I I I I 1 I
-0.1 0.1 0.3 0.5 0.7 0.9 1.1
X/C
(d)
(711
.I.5
.1.0 -_
O5 -
(I.o '
I).5
-i
1.0
-0. I
- GMBE 'q = 0.407 -I.5-
o EXl'rr q = 0.400
-1.0 -
o -
o o -0.5 -
11.0 -
0,5-
1.0 '
.0.1
o
I
- GMBE rl = 0,886
o E.X'Tq"rl = 0.900
I I I I I I I I I I -1 I I I I l I I I l l I ]
0.1 0.3 0.5 0.7 0.9 1.1 0.1 0.3 0.5 0.7 0.9 1.1
x/c x/c
(c) (0
Figure 9. Comparison of computed wing Cp with wing-tunnel data.
for nacelle installed at 11=0.34, Mach--0.77 with C1=0.55.
341
Figure 10. Surface grid and symmetry plane for HSCT cruise configuration.
Figure 1 I. Surface grid for HSCT high lift configuration.
342
JFigure 12. Blocks layout for HSCT cruise (10 blocks) and high lift (18 blocks) configurations.
343
:5: : • _ !
Figure 13a. Streamline traces for HSCT cruise configuration.
MACII
x53 GRID 1
3x27. GRID 2
33_27 GRID 3
73x33_1] GRID 4
73_33_17 GRID
73_33xl7 GRID o
73x33_.11 GRID 7
17x3]a53 GRID _,
I 7x33x53 GR ID '_
17x25_,33 bRID ltl
33_2_27 GRID ] I
33x25x27 GRID i2
73x25xll GRIL) 13
73x23x17 GRID i4
73x25_17 GRID 15
73_25xll GRID 16
17x25x'_3 GRIt) i7
17x25x53 _.,R 11) l_
Figure 13b. Streamline traces for HSCT high lift configuration at L. E. flap.
344
Figure 15. Near field blocks layout for four engines 747-200
Figure 14. Complete surface grids for 747-200.
\
Figure 16. Viscous blocks near a wing/body junction.
345



An interactive multi-block grid generation system

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