Workflow for Virtual Wind Tunnel

Altair Forum User

Hello,

 

 

 

 

there were a few questions coming up, concerning the workflow for virtual wind tunnel analysis. You can have a look at the tutorials in the help of VWT (File --> Help --> Tutorials) to get a first idea of how to set up a model from the beginning. Additionally, you will find a video on

 

 

http://training.altairuniversity.com/analysis/cfd/virtual-wind-tunnel/

 

 

 

 

 

To answer the questions in detail:

 

 

1) What CAD formats can be read into VWT

 

 

The VWT does not read CAD data directly. You have to provide an Finite Element Surface Mesh in Nastran (Fluent) format instead. This mesh can be done in HyperMesh (Engineering Solutions --> CFD user profile). HyperMesh can read solidworks, Catia, ProE, Siemens NX, STEP, Iges and other CAD formats. Go to File --> import --> geometry and choose the filter type in this menu

 

 

 

 

 

2) How should you save the Mesh File in HyperMesh?

 

 

After meshing, you need to check if your surface mesh is enclosed and of good quality. Go to the Checks Toolbar --> Edges and see for free edges and T-Connections. The status bar should say  'no edges / T-Connections were found, selected elements enclose a volume'. Next go to the element check (F10) and look for elements with poor quality (tria angle < 5°, Skew > 80), duplicates and connectivity. Clean up the failed elements. After the element check is complete, export under file --> export --> solver deck and choose Nastran (Fluent) format as solver type

 

 

 

 

 

3) Meshing Tutorials:

 

 

The tutorials on meshing can be found in the Altair HyperMesh Help, e.g. CFD-1400: Wind Tunnel Mesh

 

 

Note, that for VWT, only the 2D surface mesh is needed.

 

 

 

 

 

Best Regards

 

 

 Jan

 

ydigit

Troubleshooting tips for VWT.

 

In case VWT run does not start or appears to be doing nothing, make the following checks:

Check for a directory with Name_ of_Run _time_stamp under the run path (VWT > File > Options > AcuSolve > Run Path > Directory name for VWT run)

 

1. In case mesh_intersections.dat and/or mesh_intersections.nas  exist in this folder, it means there were some issues with .Nas file exported from HyperMesh.

 

Go back to HyperMesh and make the following checks before exporting .Nas (Fluent) file.

• Connectivity
• Duplicates
• Free Edges
• Intersections and Penetrations

Check for scaling before exporting. VWT imports in Meters.

 

2. If intersection issue is not there then, check if CAD.DIR and MESHSIM.DIR were created in the run folder (Name_ of_Run _time_stamp).

     This indicates that the meshing process was started. Open the file vwtAnalysis.MeshSim.txt in a text editor. This is meshing log file that indicates how far the meshing process went. In case volume mesh was successfully created, the last few lines of this file would be similar to:

 

acuMeshSim: --------------------------------------------------------------
acuMeshSim:              Number of Nodes =
acuMeshSim:           Number of Elements =
...
acuMeshSim:            Total Memory Size =e+002 Mbytes

 

If such a section is missing from this file, it probably means that RAM on the computer was not enough for meshing. Either use a computer with higher RAM or reduce the element size.

 

 

...TBC