Geometry Generation for Cart3D Tutorial
This component of the Cart3D tutorial will walk through the process of creating a simple geometry to analyze with Cart3D. For this example, we will build a model of the Onera M6 wing.
Onera M6 Definition
The Onera M6 wing is a standard transonic test case frequently used to demonstrate CFD codes. The geometry, experimental setup, and experimental results are documented in AGARD AR-138. These results are also summarized by the NASA NPARC Alliance Validation Archive.
The Onera M6 wing uses uses an Onera D airfoil normal to the 40.18% chord line. VSP generally works with airfoils specified in the streamwise direction. The NPARC Alliance web site includes a Fortran program to transform the airfoil coordinates; it also includes an airfoil file which results from the transformation. That file was modified to create an airfoil in the VSP airfoil format. The Onera M6 airfoil file is available here.
The planform of the Onera M6 wing is depicted in the following figure pulled from AGARD AR-138. This image has been cropped and rotated slightly so it is ready-to-use as a background image in VSP; you may want to save a copy of the image for that purpose. The simplicity of the Onera M6 makes use of a background image somewhat unnecessary, but this does provide a good example of using a background image.
The Onera M6 wing is described by the following parameter values
Semispan 1.1963 m
Root chord 0.8059 m
Taper ratio 0.562
Aspect ratio 3.8
Sweep (LE) 30 deg
Building the Onera M6
As you proceed through the tutorial to build the Onera M6, remember that images have been included as thumbnails, so any place you see a picture, click on it for a larger version.
Run OpenVSP
Launch OpenVSP ready to create a new model.
Add wing component
In 'Geom Browser', choose 'MS WING' from the component type pulldown.
Click 'Add' to add the component to the model.

Delete unneeded wing sections
In 'Multi Section Wing Geom', select the 'Sect' tab.
Repeatedly click the right-facing arrow by 'Section ID:' until the most outboard wing section is active.
Repeatedly click the 'Del' button until only one wing section remains. VSP will not let you delete the last wing section.

Change model view
You may wish to rotate, zoom, or pan the model view to provide a different perspective on the model. This can be done at any time in VSP.

Add background image
VSP can display a background image in the main graphics window. This is often a good way to start a model when all you have is a three-view drawing. The Onera M6 geometry is well specified, so this step is not strictly needed. However, it still provides a good sanity check.
Save the Onera M6 planform drawing above to your hard drive.
Go to the 'Window' menu and then select 'Background…'.

In the 'Background' window, click the 'JPEG Image' button to activate a background image

In the 'Select File' window, navigate to the location where you stored the background image, select the file, and click 'Accept'.

If needed, you can scale and offset the background image so that it fits well in the display window. Close the 'Background' window when you are satisfied with the background display.
In the 'View' window, click 'Top' (or press F5) to change the view orientation to a top-view of the model.
Change driver group
There are six canonical interdependent parameters frequently used to describe a trapezoidal wing – aspect ratio (AR), taper ratio (TR), Area, Span, tip chord (TC), and root chord (RC). Usually, if three of these parameters are specified, the other three can be calculated. VSP lets the user choose which parameters to specify when building the model.
In the 'Multi Section Wing Geom' window, on the 'Sect' tab, in the 'Section Planform' area, click the 'Driver:' pulldown and then select 'AR-TR-Span'. This will activate aspect ratio, taper ratio, and span as the independent variables.

Set span and adjust view
In the 'Section Planform' area, enter '1.1963' into the box next to 'Span'. This is the semi-span of the Onera M6 wing in meters.
Adjust the pan and zoom of the model view until the wing root and tip match the background image. If you accidentally rotate the model, just press 'F5' to reset to the top view.

Set wing planform
The published Onera M6 wing parameters over-specify the wing shape and because of the limited precision included in the report, the published parameters are not perfectly self-consistent. Consequently some amount of compromise is required when modeling this wing. Each independent parameter is set by entering the value into the box to the right of the parameter.
Set the sweep to 30 degrees.
Set the taper ratio to 0.562.
Set the aspect ratio to 1.9. VSP uses the aspect ratio of a single section instead of the whole wing. Consequently, the aspect ratio is 1.9 instead of the published value of 3.8.
Pan the model until the leading edge origin aligns with the background image.

Change driver group
Click the 'Driver:' pulldown and select 'Span-TC-RC' as the driver group. This will activate span, tip chord, and root chord as the independent variables. Aspect ratio, taper ratio, and area will be calculated to agree.

Set the root chord to 0.8059.
Set airfoil section
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In the 'Multi Section Wing Geom' window, on the 'Foil' tab, click the 'Read File' button to pull up a 'Select File' dialog.

In the 'Select File' window, navigate to the location where you stored the airfoil, select the file, and click 'Accept'. This will set the root airfoil section.
Click the right-facing arrow by 'Airfoil' to change control to the tip airfoil section.
Repeat the 'Read File', navigate, 'Accept' sequence to set the tip airfoil to the Onera M6 section.
Round the wingtips
In the 'Multi Section Wing Geom' window, at the bottom of the the 'Plan' tab, click the 'Rounded Tips' button.

Change part name
In the 'Multi Section Wing Geom' window, on the 'Gen' tab, enter 'OneraWing' in the text field next to 'Name:'.

In this example, the background image has also been deactivated by clicking 'Window', 'Background…', 'JPEG Image', and then 'Cancel'.
Save model
In the 'File' window, click 'Save' to bring up a 'Select File' dialog to navigate the hard drive and specify an appropriate file name.

When you are satisfied, click 'Accept'
Next Steps
Once the geometry definition is complete, the next step is to generate a triangulated surface mesh for analysis in Cart3D. This process is detailed on the Mesh Generation page.
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Geometry Generation (This Page)
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