CD2TET

1 INTRODUCTION

CD2TET is a pre/post-processing software whose development started at the Center for Aerospace Structures at the University of Colorado at Boulder to perform, among others, the generation of the top-level input files of the three-dimensional AERO-F3D fluid code — that is, SOWER's and MATCHER's input files — from the output of the ICEM CFD mesh generation software. This User's Manual documents the basic operations of CD2TET.

2 WHAT CAN CD2TET BE USED FOR?

CD2TET can be used to perform the following tasks:

• Read a binary ICEM CFD mesh file and generate the corresponding
  • ASCII XPost (or FieldView) fluid mesh geometry file for input to the MATCHER and/or SOWER code(s).
  • ASCII FieldView mesh file for post-processing using the FieldView software.
• Create the distance-to-the-wall input file required by AERO-F for turbulent flow simulations using the Spalart-Allmaras turbulence model.
• Convert meshes from the XPost format to the Sinus format and vice versa.
• Convert meshes from the XPost or Sinus format to the ICEM CFD format. This option is useful when a mesh is generated using a different software than ICEM CFD, but the user wishes to input it to ICEM CFD for assessing its quality or editing it as follows:
  • Smoothing volume elements.
  • Identifying and correcting meshing errors.
  • Refining parts or all of the mesh.
  • Extruding prism layers.
  In addition, if only a surface mesh is available to the user, this option enables the generation of a volume mesh and/or the extraction of a faceted geometry by loading this surface mesh into ICEM CFD and performing the desired operation.
• Symmetrize a mesh with respect to a user-specified symmetry plane.

The instructions for performing the above tasks are expressed via line commands as described in LineCommandInput.

3 INPUT FILES

The CD2TET input files do not follow any naming convention. They are organized in two categories as follows.

• Input Files Generated by ICEM-CFD
• Other Input Files

3.1 INPUT FILES GENERATED BY ICEM-CFD

The most important purpose of CD2TET is perhaps to read a binary ICEM CFD mesh file and generate the corresponding ASCII XPost and/or FieldView mesh file(s) required by AERO-F's pre- and post-processing codes MATCHER and SOWER. In this case, the two input files required by CD2TET are:

• <file name>.uns. This binary mesh (or domain) input file is generated by ICEM CFD. It describes the unstructured discretization of the fluid domain. The mesh usually contains multiple surface and element sets. Each set contains a certain number of elements and is usually referred to as a subdomain. However, it is important not to confuse ICEM CFD's subdomains with those generated by Metis when applied to decompose the fluid mesh into subdomains.
• <file name>.fbc. This ASCII file specifies the boundary conditions and fluid material properties for the different subdomains defined in the mesh file. The format of this file is given in Appendix1.

• Get the CD2TET source code.
• Locate the files aerof3d, aerof3d.bcinfo and aerof3d.tcl in the directory Cd2tet.d/icemcfd/. These files constitute the source code of the AERO-F-ICEM CFD interface.
• Copy the aforementioned files to the directory ICEM_ACN/icemcfd/output-interfaces, where ICEM_ACN denotes the path to the ICEM CFD installation directory. For example, it can be /ansys_inc/v110/icemcfd/linux64_amd for the 64-bit version 11.0 of ICEM CFD or /ansys_inc/v110/icemcfd/linux for its 32-bit version 11.0.
• In the file solver_table.tcl located in the directory ICEM_ACN/icemcfd/output-interfaces, add under

       set solver_interfaces {
  

  the following line

              {{Aero-F3D}                   aerof3d     aerof3d       0 }
  

3.2 OTHER INPUT FILES

CD2TET can also be used to convert meshes from the XPost format to the Sinus format (and vice versa), create the distance-to-the-wall input file required by AERO-F for turbulent flow simulations using the Spalart-Allmaras turbulence model, and convert mesh files from the XPost or Sinus format to the ICEM CFD format. To perform any of these tasks, CD2TET requires one of the following input files:

• <file name>.top. This file contains in the XPost format the fluid mesh.
• <file name>.sinus. This file contains in the Sinus format the fluid mesh.

4 OUTPUT FILES

Unless otherwise specified by the user, the output files generated by CD2TET follow the naming convention given below. The user should also note that existing files with the same names as the files to be outputted are overwritten.

If the (mesh) input file to CD2TET is in the ICEM CFD or Sinus format, the following output files are generated by CD2TET:

• <file name>.top. This output file can be generated in either the XPost or FieldView format. It contains the fluid mesh and boundary conditions. The fluid domain is specified as an element with the name “FluidMesh”. The surface boundary conditions are organized in element sets with the following naming convention:
  • “OutletMoving” for the moving outflow boundary;
  • “InletMoving” for the moving inflow boundary;
  • “StickMoving” for the moving viscous wall boundary;
  • “SlipMoving” for the moving Euler wall boundary;
  • “Symmetry” for the symmetry boundary;
  • “SlipFixed” for the fixed Euler wall boundary;
  • “StickFixed” for the fixed viscous wall boundary;
  • “InletFixed” for the fixed inflow boundary;
  • “OutletFixed” for the fixed outflow boundary.
  The XPost and FieldView formats of a mesh file are given in Appendix2 (see also XPost's User's Manual and Appendix3, respectively).
• <file name>.top.dwall. This output file is generated in the XPost format. It contains for every mesh point its distance to the closest wall. The format of this file is described in Appendix4.

However, if the (mesh) input file to CD2TET is in the XPost format, CD2TET generates in this case the following output files:

• <file name>.sinus. This output file is created in the Sinus format. It contains the fluid mesh. The Sinus format of a mesh file is described in Appendix5.
• <file name>.sinus.dwall. This output file is generated in the Sinus format. It contains for every mesh point its distance to the closest wall.

Finally, if CD2TET is used to convert a mesh from the XPost or Sinus format to the ICEM CFD format, the following bindary output file is generated:

• <file name>.uns. This output file is created in the CD2TET binary format. It contains the fluid mesh and boundary conditions.

5 LINE COMMAND INPUT

The different line-commands for performing the various tasks described in Introduction are as follows:

• To generate the mesh and the distance-to-the-wall files in the XPost format starting from an ICEM CFD input mesh file

  cd2tet	-domain <domain file>	ICEM CFD mesh file.
  	-boco <boundary conditions file>	Boundary conditions and material properties file <name.fbc>.
  	[-output <output_file>]	Output file name. Default is icem.top (for the mesh file) and icem.top.dwall (for the distance-to-the-wall file).
  	[-fieldview]	Outputs the mesh in the FieldView format.
  	[-no_check]	Skips building interior and boundary faces and checking for ``internal'' boundary faces and negative volumes.
  	[-nowall]	Skips the generation of the distance-to-the-wall file.
  	[-xsym <location>]	Symmetrizes the mesh with respect to a plane parallel to the yz-plane and located at x=location.
  	[-ysym <location>]	Symmetrizes the mesh with respect to a plane parallel to the zx-plane and located at y=location.
  	[-zsym <location>]	Symmetrizes the mesh with respect to a plane parallel to the xy-plane and located at z=location.

  The domain and boundary conditions files are always required for the above command to work.

• To generate the mesh and distance-to-the-wall files in the XPost or Sinus format starting from a Sinus or XPost input mesh file

  cd2tet	-mesh <mesh file>	XPost or Sinus input mesh file.
  	[-output <output_file>]	Default is xpost.sinus and xpost.sinus.dwall for the Sinus output, and sinus.top and sinus.top.dwall for the XPost output.
  	[-no_check]	Skips building interior and boundary faces and checking for ``internal'' boundary faces and for negative volumes.
  	[-nowall]	Does not create the distance-to-the-wall file.
  	[-write_icem]	Outputs the mesh in the ICEM CFD format. The default is xpost.sinus.uns.
  	[-xsym <location>]	Symmetrizes the mesh with respect to a plane parallel to the yz-plane and located at x=location.
  	[-ysym <location>]	Symmetrizes the mesh with respect to a plane parallel to the zx-plane and located at y=location.
  	[-zsym <location>]	Symmetrizes the mesh with respect to a plane parallel to the xy-plane and located at z=location.

Notes:

1. by default, CD2TET computes for every mesh point its distance to the closest wall, i.e., to the “StickFixed” or “StickMoving” boundary faces; if the mesh does not contain this type of boundary faces, one must use the option -nowall because otherwise CD2TET will exit for not finding any solid wall;
2. when symmetrizing a mesh with respect to a symmetry plane, if the boundary faces that coincide with this symmetry plane are labeled “Symmetry” they are not duplicated; if the user wishes to duplicate these faces (and their corresponding nodes), he/she should not label these faces as “Symmetry”;
3. if CD2TET finds that the input mesh contains boundary faces that are surrounded by fluid elements, it prints a warning message indicating that a certain number of boundary faces are internal, and organizes these in a separate element set in the output file; this allows the user to easily visualize these faces using XPost and consequently fix the problem.

6 APPENDIX1: FORMAT OF THE BOUNDARY CONDITIONS AND FLUID VOLUME AND SURFACE IDENTIFICATION FILE GENERATED BY ICEM-CFD

The format of the boundary conditions and fluid volume identification file generated by ICEM CFD is described by the following example:

# family_boco file written by ANSYS ICEM CFD by boumosle on Wed Nov 16 09:53:31 PST 2005

## solver Aero-F3D

#ARGS noname noname noname noname noname noname noname noname noname noname noname

"WALL1"

"WALL1" "Stick" "Moving" 1 0 0 0 0 0 0 0 0 \

0 0

#ARGS noname noname noname noname noname noname noname noname noname noname noname

"WALL2"

"WALL2" "Stick" "Moving" 2 0 0 0 0 0 0 0 0 \

0 0

#ARGS noname noname noname noname noname noname noname noname noname noname noname

"OUTLET"

"OUTLET" "Outlet" "Fixed" 3 0 0 0 0 0 0 0 0 \

0 0

#ARGS noname noname noname noname noname noname noname noname noname noname noname

"SYMMETRY"

"SYMMETRY" "Symmetry" "" 4 0 0 0 0 0 0 0 0 \

0 0

#ARGS noname noname noname noname noname noname noname noname noname noname noname

"FLUID1"

"FLUID1" "FLUID" "" 1 0 0 0 0 0 0 0 0 \

0 0

#ARGS noname noname noname noname noname noname noname noname noname noname noname

"FLUID2"

"FLUID2" "FLUID" "" 2 0 0 0 0 0 0 0 0 \

0 0

Notes:

1. every line starting with a “#” is a comment line that is ignored by CD2TET;
2. every element set (referring to a fluid volume or boundary surface) name is enclosed between quotations and followed by the name of the volume or the type of boundary conditions of the surface, and 11 numbers; the first number is an integer identifying the volume or the surface; the next six real numbers are the coordinates of two points

   

   that define a rotation axis for the identified surface (for example, when it is a control surface); the last four numbers are ignored by CD2TET;

3. some versions of the ICEM CFD software output extra lines that contain the keyword “color”; such lines are ignored by CD2TET.

7 APPENDIX2: XPOST FORMAT OF A FLUID MESH

The format of an XPost fluid mesh (ASCII) file is described by the following example. Note that the comments used for explaining this format (right part of the page beginning with //) and the blank lines they induce are not part of the format. More details can be found in XPost's User's Manual.

Nodes FluidNodes	// Declaration and naming of a node set.
1 1.261110e-01 1.181100e-02 1.000000e-01	// Node number and x y z coordinates.
2 1.270000e-01 1.270000e-02 1.000000e-01
...
Elements FluidMesh_1 using FluidNodes	// Declaration and naming of an element set.
1 5 23236 165454 28776 55020	// Global element number, type and connectivity nodes.
2 5 71797 77629 962290 23279
...
Elements FluidMesh_2 using FluidNodes	// Declaration and naming of another element set.
536117 5 963129 502907 50115 60473	// Global element number, type and connectivity nodes.
536118 5 502904 502894 502896 502348
...
Elements StickMovingSurface_1 using FluidNodes	// Declaration, naming and identification of a boundary faces element set.
1 4 1 12437 67	// Global element number, type and connectivity nodes.
2 4 1 559 12437
...
Elements StickMovingSurface_2 using FluidNodes	// Declaration, naming and identification of another boundary faces element set.
1 4 30 2 12465	// Global element number, type and connectivity nodes.
2 4 2 30 12469
...
Elements OutletFixedSurface_0 using FluidNodes	// Declaration, naming and identification of another boundary faces element set.
1 4 3911 61498 12	// Global element number, type and connectivity nodes.
2 4 61498 4047 12
...

Note:

1. an integer that is appended to an element set name (and which becomes integral part of the element set name) identifies the volume or surface represented by that element set; the default (blank) integer value is 0.

8 APPENDIX3: FIELDVIEW FORMAT OF A FLUID MESH

The format of a FieldView mesh (ASCII) file is described by the following example. Note that the comments used for explaining this format (right part of the page beginning with //) and the blank lines they induce are not part of the format. More details can be found in FieldView's User's Manual.

FIELDVIEW_Grids 2 4	// Fieldview header and version identification (two integers).
Grids	// Grid declaration.
1	// Grid identification number.
Boundary Table	// Table of types of boundary conditions.
4	// Total number of types of boundary conditions in this table.
0 Symmetry	// The first entry is an integer that is either 0 if the boundary surface is not a wall, or 1 if it is a wall. The second entry is the name of the boundary condition.
0 InletFixed
0 OutletFixed
1 StickMoving
Nodes	// Declaration of a node set.
15610	// Total number of nodes in this set.
-5.000000e-01 1.000000e-01 2.667563e-04	// Nodal x y z coordinates.
-4.877294e-01 1.000000e-01 2.667563e-04
...
Boundary Faces	// Declaration of a boundary faces elements set.
31216	// Total number of boundary faces in this set.
1 3 2 1 4	// Pointer to the line of the Boundary Table, number of vertices in the face and connectivity nodes.
1 3 2 15610 1
...
Elements	// Declaration of a volume element set.
1 1 7805 7769 7807 7808	// Element type, subtype (here, always 1) and connectivity nodes.
1 1 7806 7769 7808 7807
...

9 APPENDIX4: COMMON XPOST AND SINUS FORMAT OF A DISTANCE-TO-THE-WALL FILE

The XPost (or Sinus) format of the distance-to-the-wall (ASCII) file is described by the following example. Note that the comments used for explaining this format (right part of the page beginning with //) and the blank lines they induce are not part of the format. More details on the format of a scalar result file can be found in XPost's User's Manual.

Scalar walldist under load for FluidNodes	// Declaration of a scalar result set named walldist for the node set named FluidNodes.
15610	// Total number of nodes in FluidNodes.
0.0	// Dummy time-step.
4.999433e-01	// Distance-to-the-wall value (for each node in FluidNodes).
4.876741e-01
...

10 APPENDIX5: SINUS FORMAT OF A FLUID MESH

The format of a Sinus mesh (ASCII) file is described by the following example. Note that the comments used for explaining this format (right part of the page beginning with //) and the blank lines they induce are not part of the format.

15610 45288 31216	// Total number of nodes, volume elements and boundary faces.
-5.000000e-01 1.000000e-01 2.667563e-04	// Nodal xyz coordinates.
-4.877294e-01 1.000000e-01 2.667563e-04
...
7769 7805 7807 7808	// Connectivity nodes of each volume element.
7769 7806 7808 7807
...
6	// Boundary condition type of each boundary face.
6
6
4
...
2 1 4	// Connectivity nodes of each boundary face.
2 15610 1
4 1 3
15610 3 1
...