Chimera Grid Tools User's Manual

Introduction

Chimera Grid Tools (CGT) is a software package containing a variety of pre- and post-processing tools for the Chimera overset grid approach [1] for computational fluid dynamics analysis on complex configurations. Several examples of recent computations that used CGT/EPOGS for the creation of the grid systems are shown on Figure 1. Further examples of recent applications that used CGT manual meshing and scripting tools are shown in Figure 2. The current procedure for performing overset CFD analysis on such configurations is outlined in Figure 3. A typical starting point is a description of the surface geometry in CAD format, while typical outputs from the process are force and moment coefficients, and pressure distributions of the configuration under certain specified freestream conditions. The complete suite of tools necessary to perform such a process includes CAD tools for geometry manipulation, and geometry defects elimination, Chimera Grid Tools for grid generation and post-processing [2,3], PEGASUS [4,5], DCF-Xrays [6], C3P [7] (or other equivalent tool) for domain connectivity, OVERFLOW [8], or LAVA [9] for solution computation, and FOMOCO Utilities [10,11,12], or USURP [13] for force and moment computation. Overviews on best practices for overset grid generation are given in Refs [14,15]. Individual tools used in various parts of the process are illustrated in red in Figure 3.

Figure 1: Recent Applications of Chimera Grid Tools - EPOGS

Application	Grid Figures	Volume Grid Info/Pubs/POC	Solutions/Videos/Links/Figs
Tiltwing Test Rig (TWTR) Experiment		511 grids, 156 million points Jensen, J. C., Chuen, A. M., Chan, W. M. Pre-Test CFD Analyses for the Tiltwing Test Rig Experiment AIAA 2025-3384
AIAA Drag Prediction Workshop 8 / Aeroelastic Prediction Workshop 4		35 grid systems across 15 different geometries Mesh family with 6 levels of grid resolutions for some geometries (L1: 11-16M pts, L6: 1.0-1.6B pts) Chan, W. M., Chuen, A. M., Jensen, J. C., Schauerhamer, D. G. Overset Structured Mesh Generation on Complex Configurations Using the EPOGS Toolset Submitted to AIAA Aviation Forum 2026
Various RVLT eVTOL Concept Vehicles		Chan, W. M., Chuen, A. M., Jensen, J. C. Advances in Automation of Overset Structured Volume Mesh Generation and Domain Connectivity AIAA 2024-4305
VAERA Fire-Fighting Drone		275 grids, 109 million points Chan, W. M., Peters, N. J. Overset Structured Mesh Generation on Complex Configurations Using the EPOGS Toolset Submitted to AIAA Aviation Forum 2026
Multi-Rotor Test Bed 3 (Preliminary geometry)		736 grids, 0.62 million points (surface only) Chan, W. M. Work in progress Unpublished
Isolated Ducted Propeller		361 grids, 17 million points Chuen, A. M., Hosseini, S. S., Jensen, J. C., Chan, W. M. Aerodynamic Simulations for Complex Geometries Using Automatically Generated Structured Overset Meshes AIAA 2023-3602
Juncture Flow Experiment F6 Wing/Body		439 grids, 45.5 million points Chuen, A. M., Hosseini, S. S., Jensen, J. C., Chan, W. M. Aerodynamic Simulations for Complex Geometries Using Automatically Generated Structured Overset Meshes AIAA 2023-3602

Figure 2: Recent Applications of Chimera Grid Tools - Manual/scripted meshing

Application	Grid Figures	Volume Grid Info/Pubs/POC	Solutions/Videos/Links/Figs
Artemis I		1949 grids, 1.08 billion points Dalle, D. J., Rogers, S. E., Meeroff, J. G., Burkhead, A. C., Schauerhamer, D. G., Diaz, J. F. Launch Vehicle Ascent Computational Fluid Dynamics for the Space Launch System, J. Spacecraft & Rockets, Vol. 61, No. 2, 2023
Glenn Icing Research Tunnel (IRT)		1615 grids, 795 million points Koch, J. R. Modeling effort funded by AETC to understand and map the flow of the IRT Unpublished
Dragonfly Rotorcraft Lander		342 grids, 450 million points Ventura Diaz, P., Yoon, S., Edquist, K. High-Fidelity Computational Modeling of Dragonfly Lander during Preparation for Powered Flight 81st VFS Annual Forum and Technology Display, 2025
Dragonfly Lander Test Article iin NFAC		239 grids, 280 million points Ventura Diaz, P., Yoon, S., Edquist, K. High-Fidelity Simulations of a Dragonfly Lander Test Article in the National Full-Scale Aerodynamics Complex AIAA 2025-3665
Subsonic Single Aft Engine (SUSAN) Electrofan Concept		78 grids, 109 million points Chau, T., Anibal, J. L., Lowe, B. M., Machado, L. M., Duensing, J. C. High-Fidelity Aeropropulsive Assessment of Distributed Electric Propulsion and Boundary Layer Ingestion for the SUSAN Electrofan AIAA 2025-1275
NASA Tilt-Wing Air Taxi		1082 grids, 501 million points Garcia Perez, D., Ventura Diaz, P., Sanguinetti, A., Yoon, S. Tiltwing Transition Flight Using High-Fidelity CFD 80th VFS Annual Forum and Technology Display, 2024
Iced 8.9% Scale Semispan Swept Wing		529 grids, 531 million points Craig Penner, D.,, Housman, J. A., Stich, G. D., Souza, V. C., Koch, J. R., Duensing, J. C. Wall-Modeled Large-Eddy Simulations of a Swept Wing with Leading-Edge Ice AIAA 2024-3999
Conventional Tube-and-Wing Aerodynamic Shape Optimization		20 grids, 10 million points Chau, T., Anibal, J. L., Lowe, B. M., Machado, L. M., Duensing, J. C. High-Fidelity Aeropropulsive Assessment of Distributed Electric Propulsion and Boundary Layer Ingestion for the SUSAN Electrofan AIAA 2025-1275
Boundary Layer Ingestion Inlet to Distortion Tolerant Fan (BLI2DTF)		138 grids, 44 million points Heinlein, G., Dumlupinar, E., Housman, J. A., Jensen, J. C. Performance Characteristics of a Boundary Layer Ingestion Inlet - Distortion Tolerant Fan Through CFD Code Coupling AIAA 2024-1195
NASA Open Fan		200 grids, 97 million points Fernandes, L. F., Housman, J. A., Kenway, G. K., Stitch, G. D., Kiris, C. C. Fan Noise Predictions of the NASA Source Diagnostic Test using Unsteady Simulations with LAVA Part I: Near-Field Aerodynamics and Turbulence AIAA 2023-0793
NASA Quiet Single Main Rotor (QSMR) helicopter		73 grids, 564 million points Ventura Diaz, P., Garcia Perez, D., Yoon, S. Computational Analysis of a Quiet Single-Main Rotor Helicopter for Air Taxi Operations 78th VFS Annual Forum and Technology Display, 2022
NASA Quadcopter Air Taxi		92 grids, 472 million points Ventura Diaz, P., Garcia Perez, D., Yoon, S. Computational Study of NASA Quadrotor Urban Air Taxi Concept AIAA 2020-0302
NASA Side-By-Side Air Taxi		74 grids, 300 million points Ventura Diaz, P., Johnson, W., Ahmad, J., Yoon, S. Computational Study of the Side-By-Side Urban Air Taxi Concept 75th VFS Annual Forum and Technology Display, 2019
Space Launch System Block 1		1832 grids, 800 million points Dalle, D. J., Rogers, S. E., Chan, W. M., Lee, H. C. Inviscid and Viscous CFD Analysis of Booster Separation for the Space Launch System Vehicle AIAA 2016-0797
High-Lift Common Research Model (HLCRM)		102 grids, 564 million points Chan, W. M. Best Practices on Overset Structured Mesh Generation for the High-Lift CRM Geometry AIAA 2017-0362
JAXA Standard Model (JSM)		231 grids, 243 million points Jensen, J. C., Stich, G. D., Housman, J. A., Denison, M. F., Kiris, C. C. LAVA Simulations for the 3rd AIAA CFD High-Lift Prediction Workshop using Body Fitted Grids AIAA 2018-2056
Blackhawk Helicopter in Forward Flight		14533 grids, 1290 million points Chaderjian. N. M. Navier-Stokes Simulation of UH-60A Rotor/Wake Interaction Using Adaptive Mesh Refinement, 73rd AHS Forum, 2017
Open Rotor Noise Study		303 grids, 428 million points Housman, J. A., Kiris, C. C. Structured Overlapping Grid Simulations of Contra-Rotating Open Rotor Noise AIAA 2016-0814

Tools in CGT can be grouped into the following categories: surface grid generation tools, volume grid generation tools, grid utilities, configuration automation scripts, utility scripts, and post-processing tools. See Table 1 below for a brief description of each tool, the category for which it resides, and access to more detailed documentation.

The package is organized with the following directories:

doc/

Contains documentation and sample input files for the various grid tools and scripts, as well as a log of the changes made for each release of CGT.

examples/

Contains a suite of examples to test the tools, and also includes a self-verification tool named verify to check that the tools are running properly.

gui/

Contains files for a graphical user interface called OVERGRID [16] that can be used to access the various grid tools. For a user facing a new problem, it is much easier to perform grid generation with the assistance of a graphical tool for the first time. Once the gridding strategy has been identified, scripts can be constructed to generate grids for similar configurations.

smart/

Contains files for the solution monitoring and analysis reporting tool OVERSMART [17].

include/

Contains header files that are included into various source code files through use of the preprocessor.

lib/

Contains libraries of FORTRAN and C routines that are common to many of the grid tools. These routines include computation of stretching functions, computation of grid normals, projections of grids, grid topology determination and enforcement, and many others.

scriptbin/

Contains a number of Tcl scripts which can automate the building of an overset grid system following the process illustrated in Figure 3. These scripts will build input files, execute, and provide error checking for a number of programs, including: volume grid generation ( HYPGEN [18,19] and LEGRID), volume grid smoothing ( SMOGRD) , domain connectivity using PEGASUS 5 (complete input file) or PEGSUS 4.1 (partial input file) [5], surface fringe point projection ( PROGRD ), hybrid surface grid generation for force and moment computation [10,11,12], flow solution computation using OVERFLOW [8]. See the scripts manual for more details. Such scripts have been used to create complex grid systems for high-lift configurations [20].

scriptlib/

Contains a library of Tcl script procedures that are called by some of the scripts in the scriptbin directory, and are available to the user by using the lappend auto_path scriptlib command. These procedures are also highly useful when building specific grid generation scripts.

src/

Contains the source code for the high-level batch-mode FORTRAN codes that can be run by the user.

tutorials/

Contains tutorials for

• Various modules in OVERGRID
• EPOGS (4 cases)
• Basic functions of the Script Library
• Grid-centric and component-centric approaches for building grid generation and pre-processing scripts for complex configurations

Below is a figure showing the hierarchy of the various modules in the Chimera Grid Tools package:

Components of Chimera Grid Tools

Software modules in Chimera Grid Tools consist of a main graphical interface called OVERGRID, and a number of independent tools in the form of Fortran programs or Tcl scripts that can be called in batch mode. A brief description of each tool and access to further information is given in Table 1.

Table 1: GUI and Batch Modules in Chimera Grid Tools

Program	Category	Description
OVERGRID	GUI	Graphical user interface for visualization and processing of geometry and grids, grid generation, domain connectivity and flow solver input
autobc	Grid Utility	Automatic boundary conditions determination
boxgr	Volume Grid Generation	Generation of stretched cartesian background grids and elliptic far-field grids
BuildIngrid	Configuration Automation Script	Builds the INGRID file used by PEGSUS 4.1
BuildMixsuri	Configuration Automation Script	Builds the MIXSUR/OVERINT input file from OVERFLOW input files
BuildOveri	Configuration Automation Script	Builds the OVERFLOW input files from individual "stubs"
BuildPegi/BuildPeg5i	Configuration Automation Script	Builds the PEGSUS 4.1/5.0 input file template (no hole boundaries for 4.1)
BuildPlot	Configuration Automation Script	Creates a PLOT3D command file to view family and boundary condition surfaces. Can also be used in a standalone mode with just an OVERFLOW input file. Type "BuildPlot -help" for documentation on its command-line parameters.
BuildProgrdi	Configuration Automation Script	Builds the PROGRD input file from the OVERFLOW input file information
BuildSurf	Configuration Automation Script	Runs 'make' for each component grid to update configuration surface grids
BuildVol	Configuration Automation Script	Creates volume grids via either makevol or boxgr
cad2srf (unsupported)	Surface Grid Generation	Generate surface triangulation and edge curves from native solid CAD part
cgtclean	Utility Script	Cleans output from most CGT tools
collar	Utility Script	Script to create collar grids [21]
combinemx	Grid Utility	Combine any number of PLOT3D grid files into one PLOT3D multiple grid file
combinemq	Grid Utility	Combine any number of PLOT3D Q files into one PLOT3D multiple grid Q file
compx	Grid Utility	Computation of difference between two grids
conmug	Surface Grid Generation	Auto-concatenation of multiple surface and curve grids
curvar	Grid Utility	Computation of areas bounded by one or more closed curves in an x, y, or z constant plane
cva	Post Processing	Computation of cut planes on overset grid system and solution
diffxq	Grid Utility	Computation of differences between two grid files with iblanks or two solution files
egads2srf	Surface Grid Generation	Generate discretized BREP faces BREP edges, and triangulations from IGES, STEP, or EGADS geometry files
epogs	EGADS2SRF & POGS	Automation of grid generation and input files preparation for overset CFD computations
extractsrf	Utility Script	Parses MIXSUR input file to create SPLITMX/SPLITMQ inputs for just surface info
FFIO Library	General I/O Library	Library for file I/O for grid, flow solution, triangulation, x-ray map, domain connectivity data files
gencore	Volume Grid Generation	Generation of H-topology volume grid inside core of a tube
genpipe	Surface Grid Generation	Generation of constant diameter pipe surface grid from 3-D centerline curve
gen_x	Grid Utility	Domain connectivity pre-processing tool for creating object images
grided	Grid Utility	Compilation of a variety of grid editing functions for structured grids
gridinf	Grid Utility	Computes basic grid information
hypgen	Volume Grid Generation	Generation of a hyperbolic volume grid from a single surface grid [18,19]
hypin	Volume Grid Generation	Generation of normal spacing function for volume grids
intchk	Grid Utility	Domain connectivity donor stencil quality checks
intgrd	Surface Grid Generation	Generation of a new surface grid onto a reference grid via interpolation
loadis	Post Processing	Computation of sectional force coefs on components
lsect	Surface Grid Generation	Find intersection curve between one intersector surface grid and multiple intersectee surface grids
makevol	Utility Script	Creates a volume grid via HYPGEN/LEGRID, and runs SMOGRD using OVERFLOW input file
minterp	Post Processing	Interpolation of single/multiple grid and solution files
mixsur	Post Processing	Generation of hybrid surface grid for force/moment computation
overConvert	Grid Utility	Convert various files used in overset grid computations (x,q,X-ray,INTOUT,XINTOUT,tri,triq) between different formats
oversmart	Post Processing	Generation of solution convergence plot matrices from OVERFLOW history files
overhist	Post Processing	Extraction of residual and flow coefficients data from OVERFLOW history files
overint	Post Processing	Integration of force/moment and mass flow rate coefficients
overplot	Post Processing	GUI for plotting flow coefficients and sectional Cp cuts on components
pip	Grid Utility	Mass properties calculator
plothole	Post Processing	Creates PLOT3D command file for PEGSUS 4.1 boundaries
PreVol	Configuration Automation Script	Builds OVERFLOW input files, config.tcl, inputs.tcl from surface grid file
p3dtrans	Grid Utility	Conversion of PLOT3D format for curve grids to/from 2/3-column xyz data format
pogs	Grid Utility	Pre-Processor for Overset Grids Simulations
progrd	Grid Utility	Projection of points onto a collection of reference grids
qed	Grid Utility	Compilation of a variety of solution editing functions for structured grids
qinfo	Post Processing	Report OVERFLOW and PLOT3D solution-file information
recurv	Grid Utility	Grid-point redistribution
reord	Grid Utility	Grid-point re-ordering for a single grid-line
RunPeg	Configuration Automation Script	Runs BuildIngrid, pegsus41, and PROGRD using configuration information
runepogs	EPOGS Meshing Generation Script	Runs EGADS2SRF and POGS for list of cases with reporting of grid stats and timings
sblock (deprecated)	Surface Grid Generation	Partial surface domain decomposition and grid generation [22] (No longer supported)
ScriptClean	Configuration Automation Script	Cleans up .srf, .vol, .mvlog, etc. files for an entire configuration
scriptlib	Configuration Automation Script	Script library containing many Tcl procedures for grid scripts
seamcr	Surface Grid Generation	Automatic seam curve extraction and spider web grid generation [23]
seamcrt	Surface Grid Generation	Surface curves creation on surface triangulations
setzeta	Volume Grid Generation	Generate normal grid-spacing file zetastr.i for HYPGEN program
shftgrd	Grid Utility	Shifting/translating grid coordinates of a specified subset
smogrd	Grid Utility	Perform elliptic smoothing in selected grid subset to spread out region of fine spacing
smooth	Grid Utility	Smooth grid by performing second order smoothing
smosurf	Grid Utility	Perform grid spacing smoothing in one direction for volume grids
splitmx	Grid Utility	Extraction of arbitrary grid subsets from PLOT3D multiple grid file
splitmq	Grid Utility	Extraction of arbitrary q subsets from PLOT3D multiple grid q file
srap	Grid Utility	Perform splining, grid point redistribution and projection on curves/surfaces
srf2cad (unsupported)	Surface Grid Generation	Project structured surface grid back to native solid CAD part
srf2egads (untested)	Surface Grid Generation	Project structured surface grids onto IGES, STEP, or EGADS geometry files
str2tri	Grid Utility	Convert PLOT3D multiple structured surface panels to CART3D surface triangulation
strchk	Grid Utility	Computation and display of local stretching ratio info for grids
stretch	Grid Utility	Evaluation and display of 1D stretching functions
surgrd	Surface Grid Generation	Generation of a new surface grid onto a collection of reference grids via hyperbolic/algebraic surface grid generation [24]
Tscan	Utility Script	Computation of cross sectional area of a triangulated object versus x, y or z
triged	Grid Utility	Compilation of a variety of grid editing functions for surface triangulations
triload	Post Processing	Generation of line loads from surface triangulation grid and solution file [25]
usurp	Post Processing	Integration of force/moment and mass flow rate coefficients on overset surface grids using polygon clipping
vpro	Post Processing	Interpolate velocity profiles from a grid and solution at specified surface normals or lines
wingcap	Surface Grid Generation	Generation of surface grid in tip region of wing
wkcut	Surface Grid Generation	Generation of surface grid in wake region
xinted	Grid Utility	Perform various combination functions to grid, XINTOUT and INS3D bc files
xrayed	Grid Utility	Perform various operations on Xray files with multiple Xrays in each

What's New in Version 3.0

New tools and capabilities in version 3.0 include

• EPOGS - consists of 2 tools: egads2srf and pogs for performing automatic overset mesh generation and preparation of input files for flow solver and component aerodynamic loads computation
• FFIO update - updated library for detection and i/o of all files used in overset CFD analysis process. New features include C function calls API, subrecords treatment for records exceeding 32-bits in size
• Bladegen - tool for rotor/propeller blade mesh generation

Further details are described in cgt3.0.html

Tutorials

Tutorials for some of the main tools are contained in the chimera3.0/tutorial directory where the tutorial for each tool is contained in its own subdirectory (listed below). It is recommended that all users go through the OVERGRID tutorial first. Most users should also attempt the Script Library tutorial to gain basic experience in building grid generation scripts. Users interested in EPOGS should go through the EPOGS tutorial after trying at least the OVERGRID tutorial.

• overgrid - OVERGRID graphical user interface tutorial for interfacing with multiple pre- and post-processing modules of CGT.
• scriptlib - Script Library tutorial on basic grid generation scripts construction.
• epogs - EPOGS auto-meshing toolset tutorial that goes through the various capabilities of the toolset.
• bladegen - Blade geometry auto-meshing tool tutorial that goes through the various capabilities of the tool.
• scripts - Grid-centric configuration scripts tutorial that goes through an example on building grids using the grid-centric paradigm (Build* scripts).
• jclv - This tutorial uses a generic rocket example to illustrate development of a complete overset grid CFD simulation script using two different paradigms: (1) grid-centric, (2) component-centric.

Authors Information

Many people have contributed to the different parts of Chimera Grid Tools. A summary of the tools/scripts and their application is shown in Table 1. See the documentation for the individual tool to determine authorship. Questions and suggestions can be directed to the corresponding authors (see Table 2).

References

1. Steger, J. L., Dougherty, F. C. and Benek, J. A., "A Chimera Grid Scheme," Advances in Grid Generation , K. N. Ghia and U. Ghia, eds., ASME FED-Vol. 5, June, 1983.
2. Chan, W. M.," Advances in Software Tools for Pre-processing and Post-processing of Overset Grid Computations ," in Proceedings of the 9th International Conference on Numerical Grid Generation in Computational Field Simulations, San Jose, California, June, 2005.
3. Chan, W. M., CAD Interface, Strand Grid Technology, and Other New Developments in Chimera Grid Tools 2.0 , Proceedings of the 8th Symposium on Overset Composite Grids and Solution Technology, Houston, Texas, October, 2006.
4. Rogers, S. E., Suhs, N. E., Dietz, W. E., " PEGASUS 5: An Automated Preprocessor for Overset-Grid Computational Fluid Dynamics ," AIAA Journal, Vol. 41, No. 6, pp. 1037-1045, 2003.
5. Suhs, N. E., Dietz, W. E., Rogers, S. E., Nash, S. M. and Onufer, J. T., " PEGASUS User's Guide ," Version 5.1c, NASA Ames Research Center, July, 2000.
6. Meakin, R. L., "Object X-rays for Cutting Holes in Composite Overset Structured Grids," AIAA Paper 2001-2537, 2001.
7. Chan, W. M. and Pandya, S. A., "Advances in Distance-Based Hole Cuts on Overset Grids," AIAA Paper 2015-3425, 2015.
8. Nichols, R. H., Tramel, R. W. and Buning, P. G., "Solver and Turbulence Model Upgrades to OVERFLOW 2 for Unsteady and High-Speed Applications," AIAA Paper 2006-2824, 2006.
9. Kiris, C., Housman, J., Barad, M., Brehm, C., Sozer, E., and Moini-Yekta, S., "Computational Framework for Launch Ascent and Vehicle Aerodynamics," Aerospace Science and Technology, 55, 189--219, August, 2016.
10. Chan, W. M.," Enhancements to the Hybrid Mesh Approach to Surface Loads Integration on Overset Structured Grids ," AIAA Paper 2009-3990, June, 2009.
11. Chan, W. M. and Buning, P. G., "Zipper Grids for Force and Moment Computation on Overset Grids," AIAA Paper 95-1681, in Proceedings of the 12th AIAA Computational Fluid Dynamics Conference, 1995.
12. Chan, W. M. and Buning, P. G.," User's Manual for FOMOCO Utilities - Force and Moment Computation Tools for Overset Grids ," NASA TM~110408, July, 1996.
13. Boger, D. and Dreyer, J., "Prediction of Hydrodynamic Forces and Moments for Underwater Vehicles Using Overset Grids," AIAA Paper 2006-1148, 44th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, Jan., 2006.
14. Chan, W. M., Gomez, R. J., Rogers, S. E. and Buning, P. G., " Best Practices in Overset Grid Generation ," AIAA Paper 2002-3191, 32nd AIAA Fluid Dynamics Conference, St. Louis, Missouri, June, 2002.
15. Pandya, S. A., Chan, W. M., Kless, J.," Automation of Structured Overset Mesh Generation for Rocket Geometries ," AIAA Paper 2009-3993, June, 2009.
16. Chan, W. M.," The OVERGRID Interface for Computational Simulations on Overset Grids ," AIAA Paper 2002-3188, 32nd AIAA Fluid Dynamics Conference, St. Louis, Missouri, June, 2002.
17. Kao, D. L., Chan, W. M.," OVERSMART - A Solution Monitoring and Reporting Tool for the OVERFLOW Flow Solver ," AIAA Paper 2009-3998, June, 2009.
18. Chan, W. M. and Steger, J. L., "Enhancements of a Three-Dimensional Hyperbolic Grid Generation Scheme," Appl. Math. and Comput. 51 , 181--205, 1992.
19. Chan, W. M., Chiu, I.-T., and Buning, P. G., " User's Manual for the HYPGEN Hyperbolic Grid Generator and the HGUI Graphical User Interface ," NASA TM 108791, October, 1993.
20. Rogers, S. E., Roth, K., Nash, S. M., Baker, M. D., Slotnick, J. P., Whitlock, M., and Cao, H. V.," Advances in Overset CFD Processes Applied to Subsonic High-Lift Aircraft ," AIAA Paper 2000-4216, 18th AIAA Applied Aerodynamics Conference, Denver, Colorado, August, 2000.
21. Parks, S. J., Buning, P. G., Steger, J. L., and Chan, W. M., "Collar Grids for Intersecting Geometric Components Within the Chimera Overlapped Grid Scheme," AIAA-91-1587, Proceedings of the 10th AIAA Computational Fluid Dynamics Conference, Honolulu, HI, June 24-26, 1991.
22. Chan, W. M. and Meakin, R. L.," Advances Towards Automatic Surface Domain Decomposition and Grid Generation for Overset Grids ," AIAA Paper 97-1979, Proceedings of the 13th AIAA Computational Fluid Dynamics Conference, Snowmass, Colorado, 1997.
23. Chan, W. M. and Gomez, R. J.," Advances in Automatic Overset Grid Generation Around Surface Discontinuities ," AIAA Paper 99-3303, Proceedings of the 14th AIAA Computational Fluid Dynamics Conference, Norfolk, Virginia, 1999.
24. Chan, W. M. and Buning, P. G., "Surface Grid Generation Methods for Overset Grids," Computers and Fluids , 24 , No. 5, 509--522, 1995.
25. Pandya, S. A. and Chan, W. M.," Computation of Sectional Loads from Surface Triangulation and Flow Data ," AIAA Paper 2011-3680, 20th AIAA Computational Fluid Dynamics Conference, Honolulu, Hawaii, June, 2011.
26. Chan, W. M., Pandya, S. A. and Haimes, R., "Automation of Overset Structured Surface Mesh Generation on Complex Geometries ," AIAA Paper 2019-3671, AIAA Aviation Forum, Dallas, TX, June, 2019.
27. Chuen, A. M. and Chan, W. M., "Overlap Preservation Using Loosely-Coupled Boundary Conditions for Body-Fitted Structured Overset Grids, " AIAA Paper 2022-0216, AIAA SciTech Forum, San Diego, CA, Jan 2022.
28. Chan, W. M., Pandya, S. A. and Chuen, A. M., "Automation of Overset Structured Surface Mesh Generation on Boundary Representation Geometries, " AIAA Paper 2022-3607, AIAA Aviation Forum, Chicago, IL, Jun 2022.
29. Chuen, A. M., Hosseini, S. S., Jensen, J. C., Chan, W. M., "Aerodynamic Simulations for Complex Geometries Using Automatially Generated Structured Overset Meshes, " AIAA Paper 2023-3602, AIAA Aviation Forum, San Diego, CA, Jun 2023.
30. Hosseini, S. S., Chuen, A. M., Chan, W. M., "Computational Aerodynamics Study of the Lift+Cruise VTOL Concept Vehicle Components," 6th Decennial VFS Aeromechanics Specialists' Conference, Santa Clara, CA, Feb 2024.
31. Chan, W. M., Chuen, A. M. and Jensen, J. C., "Advances in Automation of Overset Structured Volume Mesh Generation and Domain Connectivity, " AIAA Paper 2024-4305, AIAA Aviation Forum, Las Vegas, NV, Aug 2024.
32. Chan, W. M., Chuen, A. M., Jensen, J. C., Schauerhamer, D. G., "Overset Structured Mesh Generation on Complex Configurations Using the EPOGS Toolset", AIAA Paper 2026-4121, AIAA Aviation Forum, San Diego, CA, June, 2026.

AMS Seminars on OVERGRID

A three-part tutorial on the various features of OVERGRID under the Advanced Modeling and Simulation (AMS) Seminar Series at NASA Ames Research Center can be found at

Chan, W. M., The OVERGRID Graphical User Interface in Chimera Grid Tools (Part 1) , AMS Seminar Series, May 13, 2014.

Chan, W. M., The OVERGRID Graphical User Interface in Chimera Grid Tools (Part 2) , AMS Seminar Series, May 20, 2014.

Chan, W. M., The OVERGRID Graphical User Interface in Chimera Grid Tools (Part 3) , AMS Seminar Series, May 29, 2014.

AMS Seminars on Automatic Overset Mesh Generation and EPOGS

Several AMS seminars have been given on the automation scheme for overset mesh generation and various test cases. These can be found at

Chan, W. M. and Chuen, A. M. Recent Developments on Automation of Overset Structured Mesh Generation , AMS Seminar Series, Jan 27, 2022.

Chuen, A. M. and Chan, W. M. A Study on Flow Solutions Computed on Automatically and Manually Generated Structured Overset Meshes , AMS Seminar Series, Sep 21, 2023.

Chan, W. M. Recent Development and Applications of the EPOGS Toolset for Automatic Structured Overset Mesh Generation , AMS Seminar Series, Jan 23, 2025.

Sponsors

Funding for this work has been partially provided by

• The NASA Subsonic Vehicle Technologies and Tools (SVTT) Project
• The NASA Revolutionary Vertical Lift Technology (RVLT) Project
• The NASA Transformational Tools and Technology (TTT) Project
• The NASA Subsonic Flight Demonstrator (SFD) Project

Past sponsors include

• The NASA Space Launch Systems Program
• The NASA Constellation Program under the Ares, Ground Operations, and Simulation-Assisted Risk Assessment (SARA) projects
• The DOD HIARMS project
• The NASA CICT/CNIS Program
• The NASA High Performance Computing and Communications Program
• The DOD High Performance Computing Modernization Program under the CHSSI CFD-4 Project
• The NASA Advanced Subsonic Technology Program
• The NASA Space Shuttle Program

Acknowledgements

A number of colleagues have provided valuable comments and code fragments to the development of CGT at various times. It would be difficult to list and thank them all. A partial list includes

• Darby Vicker (Amentum Technology/NASA JSC)
• Jeff Housman (NASA Ames)
• Marian Nemec (NASA Ames)
• Gerrit-Daniel Stich (Analytical Mechanics Associates/NASA Ames)
• Brad Richardson (Amentum Technology/NASA JSC)

• Patricia Ventura Diaz (Analytical Mechanics Associates/NASA Ames) and Chip Jackson (NASA Langley) for help in testing the software
• John Hardman (Analytical Mechanics Associates/NASA Ames) for his work on improving the CGT main webpage

Software Request Procedure

This software package can be requested and used by U.S. citizens and permanent residents belonging to a U.S. organization. The request can be made from the NASA Software Catalog

Copyright, Notices and Disclaimers

The following copyright, notices and disclaimers apply to all modules and libraries of the Chimera Grid Tools software package.

Copyright and Notices

Chimera Grid Tools 3.0

Copyright 2004, 2007, 2010, 2018, and 2026 United States Government as represented by the Administrator of the National Aeronautics and Space Administration. All Rights Reserved.

Unique Surface Using Ranked Polygons (USURP)

Copyright 2005 The Pennsylvania State University. All Rights Reserved. USURP is a tool bundled with CGT 3.0 and distributed with permission under license from the Pennsylvania State Research Foundation. Portions of USURP created by David Boger under funding provided by Office of Naval Research, NASA, and the Applied Research Laboratory.

The CGT 3.0 software and documentation shall not be provided to foreign persons (as defined by 22 CFR § 120.16). It is available to U.S. citizens and permanent residents (as defined in 8 U.S.C. § 1101(a)(20)) only after signing the SUA.

The CGT 3.0 software and documentation shall not be distributed to any third parties without NASA’s consent, nor shall it be provided to any person (as defined by 22 CFR §120.14) on the Consolidated Screening List available at Consolidated Screening List.

CGT 3.0 is a software package used for performing pre- and post-processing of computational fluid dynamics analysis on complex configurations using overset grids. This software is provided without any express or implied warranties, as a collection of software tools for which the accuracy, reliability, and applicability of results generated by CGT 3.0—including all solvers, modules, and post-processing tools—depend on the user's modeling choices, input data, and verification efforts.

By using this software, you acknowledge that you are solely responsible for validating results and ensuring their suitability for your intended purpose. NASA, the CGT 3.0 development team, and all contributors or distributing parties assume no liability for any outcomes, damages, or losses arising from the use or misuse of this software.

See the related Software Usage Agreement/License for additional disclaimer, waiver and other liability provisions that apply to the software.

This software may only be used, reproduced, and provided to others as permitted under the terms of the agreement under which it was acquired from the U.S. Government. Otherwise, this software may not be redistributed, shared, or transferred to any unauthorized third parties without explicit permission from the appropriate NASA authorities. Neither title to, nor ownership of, the software is hereby transferred. This notice shall remain on all copies of the software.

Disclaimers

THE SOFTWARE AND/OR TECHNICAL DATA ARE PROVIDED "AS IS" WITHOUT ANY WARRANTY OF ANY KIND, EITHER EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, ANY WARRANTY THAT THE SOFTWARE AND/OR TECHNICAL DATA WILL CONFORM TO SPECIFICATIONS, ANY IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR FREEDOM FROM INFRINGEMENT, ANY WARRANTY THAT THE SOFTWARE AND/OR TECHNICAL DATA WILL BE ERROR FREE, OR ANY WARRANTY THAT TECHNICAL DATA, IF PROVIDED, WILL CONFORM TO THE SOFTWARE. IN NO EVENT SHALL THE UNITED STATES GOVERNMENT, OR ITS CONTRACTORS OR SUBCONTRACTORS, BE LIABLE FOR ANY DAMAGES, INCLUDING, BUT NOT LIMITED TO, DIRECT, INDIRECT, SPECIAL OR CONSEQUENTIAL DAMAGES, ARISING OUT OF, RESULTING FROM, OR IN ANY WAY CONNECTED WITH THIS SOFTWARE AND/OR TECHNICAL DATA, WHETHER OR NOT BASED UPON WARRANTY, CONTRACT, TORT, OR OTHERWISE, WHETHER OR NOT INJURY WAS SUSTAINED BY PERSONS OR PROPERTY OR OTHERWISE, AND WHETHER OR NOT LOSS WAS SUSTAINED FROM, OR AROSE OUT OF THE RESULTS OF, OR USE OF, THE SOFTWARE AND/OR TECHNICAL DATA.

THE UNITED STATES GOVERNMENT DISCLAIMS ALL WARRANTIES AND LIABILITIES REGARDING THIRD PARTY COMPUTER SOFTWARE, DATA, OR DOCUMENTATION, IF SAID THIRD PARTY COMPUTER SOFTWARE, DATA, OR DOCUMENTATION IS PRESENT IN THE NASA SOFTWARE AND/OR TECHNICAL DATA, AND DISTRIBUTES IT "AS IS."

RECIPIENT AGREES TO WAIVE ANY AND ALL CLAIMS AGAINST THE UNITED STATES GOVERNMENT AND ITS CONTRACTORS AND SUBCONTRACTORS, AND SHALL INDEMNIFY AND HOLD HARMLESS THE UNITED STATES GOVERNMENT AND ITS CONTRACTORS AND SUBCONTRACTORS FOR ANY LIABILITIES, DEMANDS, DAMAGES, EXPENSES OR LOSSES THAT MAY ARISE FROM RECIPIENT'S USE OF THE SOFTWARE AND/OR TECHNICAL DATA, INCLUDING ANY DAMAGES FROM PRODUCTS BASED ON, OR RESULTING FROM, THE USE THEREOF.

IF RECIPIENT FURTHER RELEASES OR DISTRIBUTES THE NASA SOFTWARE AND/OR TECHNICAL DATA, RECIPIENT AGREES TO OBTAIN THIS IDENTICAL WAIVER OF CLAIMS, INDEMNIFICATION AND HOLD HARMLESS AGREEMENT WITH ANY ENTITIES THAT ARE PROVIDED WITH THE SOFTWARE AND/OR TECHNICAL DATA.