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Unstructured Block Initialisation

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Old   March 31, 2022, 10:23
Default Unstructured Block Initialisation
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Ethan Whiting
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I'm trying to initialize an unstructured block within an S-Duct. The boundary layer was created using a structured surface domain and then using a normal extrusion inwards. The bulk flow domain should be unstructured.
I have set the wall domains to wall in the BCs tab of the solve settings and the inlet/outlet as match as I have been following the pipe inlet/outlet tutorial.

However, when initializing the unstructured block the following dialog is produced.

One of more entities could not be initialized

Isotropic tets could not be formed. Try setting other isotropic attributes.

I've attached a screenshot of the mesh and BC settings.
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File Type: png S-Duct.png (146.6 KB, 5 views)
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Old   April 1, 2022, 10:58
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Chris Sideroff
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The screenshot is too small to see what's going one. Can you post a larger image?

Since you're using structured domains on the wall for an internal flow case, I can probably make a good guess. First, do the surface quads of the structured domains have high'ish aspect ratios, greater than, say, 5? If so, what happens is that when the layers grow inward, the aspect ratio quads on the extrusion front progressively increase. This will result in very slender pyramids at the extrusion-to-iso transition and can cause issues for iso tet mesher.

Tip: you should consider using the T-Rex unstructured mesher for the whole mesh as opposed to the normal extrusion + isotropic tet mesh. T-Rex will generate as good, and usually better, boundary layer cells than the normal extrusion and complete the entire mesh in 1 step. This makes subsequent improvement of the mesh much more robust. And if you're using the normal extrusion simply because need a certain number of complete layers, there is a T-Rex parameter called "Full Layers" that can achieve a similar effect.

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