Extruding a Structured Domain Out of an Airfoil

Normal extrusions can be a powerful tool when creating structured domains off airfoils and wings. There are several parameters in the Attributes tab that can be used to extrude your mesh with great control and precision.

This exercise will create a structured domain off a connector on the upper curve of a NACA 0012 airfoil using Normal extrusion. The connector has 51 grid points assigned and the spacing constraints at the leading and trailing edges have been set to 0.001.

1. Click on Structured on the toolbar.
2. Select the connector.
3. To obtain the best results from your extrusion, we always recommend that you make sure you have enough grid points to resolve the surface curvature and that there are no significant spacing discontinuities along the length of the edge you are extruding. The Examine, Length Ratio diagnostic function can be used to ensure the point distribution is smooth along the connector or edge you are extruding.

We will now create a structured domain off the upper connector using a Normal extrusion.

4. Create, Extrude, Normal
5. Click on the Attributes tab.
6. Check the Step Size frame.
7. Set Initial Δs to 0.0005.
8. Notice how this number is smaller than the Minimum Surface Spacing of 0.001 in this case. It is a good rule of thumb to set your initial Initial Δs to a value equal to or less than your Minimum Surface Spacing to get the best results from your extrusion.

9. Check the Orientation frame.
10. Click Flip if the arrows do not point outwards.

If you check the Extrusion Method frame, you will notice two options - Hyperbolic and Algebraic. The Hyperbolic method will only be available for structured extrusions. It solves a system of hyperbolic PDEs. The Algebraic method can be used for a structured extrusion but it is a numerical approximation of the Hyperbolic method. It was developed primarily for performing unstructured extrusions. We always recommend using the Hyperbolic method for structured extrusions for best results.

11. Check the Smoothing Parameters frame.
12. Set Volume to 0.3.
13. The Volume smoothing ranges from 0.0 to 1.0 and has a default value of 0.5. This smoothing determines how rapidly grid clustering in the front will relax. A value of 0.0 will allow clustering to remain intact throughout the extrusion to the final boundary step.

You can see a comparison of the effect of near-extreme values for Volume smoothing on this extrusion in the image below.

14. Go to the Boundary Conditions tab.
15. Select both end of the connectors.
16. Set the Type to Symmetry Y.
17. Set Boundary Condition
18. Go to the Run tab and enter 80 for the Steps.
19. Run

20. You should get the following extruded domain.

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