Release of Chimera Grid Tools Version 3.0

To obtain a copy, visit the NASA Software Catalog

CGT 3.0 has been ported to the following OS and compilers

• Linux
• GNU (gfortran, gcc, g++) version: 8, 9, 10, 11, 12, 13, 14, 15
• Intel (ifort, icc, icpc) version: 2023, 2024
• Intel (ifx, icx, icpx) version: 2024
• Mac OS
• GNU (gfortran, gcc, g++) version: 12, 13, 14, 15

For Windows users utilizing WSL, review https://learn.microsoft.com/en-us/windows/wsl/tutorials/gui-apps and then install CGT following the normal Linux procedures. Existing users of CGT have reported successful builds with earlier versions of CGT using this method, but the authors have not attempted this themselves.

New Tools and Libraries

• EPOGS - A software toolset for automation of pre-processing of overset structured mesh computational fluid dynamics (CFD) analysis. This toolset consists of two tools: EGADS2SRF and POGS.
• EGADS2SRF - A tool for generating grid files used as starting point for overset surface mesh generation from a Boundary Representation (BREP) solid geometry definition file in IGS, STP or EGADS format. Output files include surface triangulation, discretized BREP faces in untrimmed structured grid patches with iblanks, discretized BREP edges, and a BREP edge/face topology data file.
• POGS (Pre-Processor for Overset Grid Simulations) – A tool for auto-generation of overset structured surface and volume meshes, domain connectivity data, input files for OVERFLOW and LAVA flow solvers, and input file for forces/moments computation using the FOMOCO/USURP tools in CGT. Input files for POGS are auto-generated by EGADS2SRF.
• Current status
• The main objective of the development of EPOGS is to automate overset structured mesh generation and creation of various input files needed for flow computation.
• The chance of success in using EPOGS is significantly enhanced if the BREP geometry follows the best practices outlined in EPOGS Workflow
• While a significant reduction in the mesh generation time has been demonstrated, manual repairs on a small fraction of meshes are typically needed. These may include
• regeneration of hyperbolic near-body volume mesh to remove negative Jacobians and self-intersections (0 - 1% of meshes)
• regeneration of near-body surface/volume meshes to improve mesh overlap (0 - ~10% of meshes)
• A sample of recent applications and related publications of EPOGS and are shown in the CGT main page
• The following new tutorials are available for EPOGS:
• Wingbody – a simple wing/body case with introductory exercises for the entire process.
• Drone – a test case involving components in relative motion: a mainbody, a set of clockwise-rotating blade, and a set of counter-clockwise rotating blades.
• L+C – a test case on a full eVTOL vehicle (the Lift+Cruise from the NASA RVLT Project). Components include fuselage, wing, htail, vtail, booms, landing-gears. This example is used to illustrate options for (1) the symmetric configuration treatment, and (2) face mesh reconstruction.
• RunCases - an example on using the runepogs script to setup and run a collection of cases.
• FFIO Library - New capabilities added include
  • Subrecords I/O for handling large grid/solution files that exceed the 32-bit record marker limit in a single grid
  • Binary (no record markers) I/O for PLOT3D grid files
  • C API for calling library from C code

• BladeGen – A tool for auto generation of rotor blade grids from sectional definitions using CGT low level library functions.

Enhancement to existing modules in alphabetical order

• BOXGR - Added auto-splitting of large grids into smaller grids with specifiable split direction
• Build Scripts - Improved internal process and data consistency
• CVA - Added option to write csv format
• DIFFXQ - Enabled differencing of files with different attributes such as IFORM, IMG, etc.
• GRIDED - New options were added include
• reset the iblank value for a specified subset.
• copy iblank value at L=1 to all other L locations.
• extract iblanks from XINTOUT file and substitute into grid file.
• GRIDINF - New options were added to output histograms for
• grid stretching ratios.
• grid spacings relative to a given reference grid spacing.
• turning angle.
• grid size.
• INTCHK – New features include
  • allowance of zero donor stencil grid number for orphan points.
  • reporting of donor stencil interpolation coefficients with distance from fringe point to interpolated point.
  • checking of L index compatibility of near-body grid donor stencils for fringe points at L=2.
• MINMAX – Added reporting of number of grids with negative Jacobians.
• OVERCONVERT – This utility was completely rewritten from a C code to a Fortran 95 code, and now uses the FFIO Library for all its functions.
• MIXSUR – Added output of prism volumes histogram and fixed various bugs related to uninitialized variables, array deallocation, axis topology detection.
• OVERGRID
• Files i/o were converted to use the latest FFIO Library.
• Code was updated to be compatible with Tcl/Tk up to version 8.6.17 or earlier, but not 9.0.*.
• OVERINT – Added capability to read q.turb from OVERFLOW, and extract turbulent eddy viscosity at the wall for inclusion in computation of viscous forces, allowing for modeling of wall roughness.
• OVERSMART - Updated code to be compatible with python 3. Introduced proper prototyping for all C functions.
• PROGRD – Converted code from Fortran 77 to Fortran 95 format.
• SBLOCK - This tool has been removed from the list of compiled tools and is currently no longer supported. The source code remains in the src directory.
• SRAP – Added ability to carry iblank information from original to redistributed grid, and fixed various bugs.
• SURGRD
• Updated snap to edge test for determination of initial curve vertex location on surface triangulation.
• Introduced NSUB optional input parameter for sub-steps.
• Replaced projection scheme with a walking scheme for multiple panel network reference surface when donor cell is oscillating between two surfaces on each side of a sharp edge.
• TRIGED
• Improved robustness and speed of DIFFTRIQ function.
• Added output of edge dihedral angle min/max and histogram.
• Added capability to compute differences in face-centered Q data.
• AUTOBC,COMPX,DIFFXQ,INTCHK,MIXSUR,OVERINT,PROGRD,SEAMCR,SEAMCRT,SURFLOBC - Implemented FFIO Library calls for file i/o.
• COMPX,SEAMCR,SURFLOBC,WKCUT – Converted code from Fortran 77 to Fortran 95 format.
• LOADIS,MINTERP,VPRO - Converted code to use Fortran allocatable arrays.
• Various bug fixes and minor improvements have been made to the following modules: BOXGR, COMBINEX, COMBINEQ, CVA, DIFFXQ, GEN_X, HYPGEN, QINFO, SMOOTH, SPLITMX, SPLITMQ, XRAYED, Script Library.
• Dynamic array allocations for all tools/libraries in CGT were converted from pointers to allocatables.

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