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[ICEM] Bad Quality Hybrid Mesh External Flow

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Old   March 8, 2020, 02:22
Default Bad Quality Hybrid Mesh External Flow
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Hi everyone,
I am meshing an external flow of a train using both structured and unstructured mesh (hexa mesh generated from the blocks for the train upper body and unstructured tetra mesh for the train underbody parts e.g. fairing, bogie, cowcatcher, etc). I merged those mesh using merge nodes options and created a hybrid mesh,

What I have done:
1. I imported the 3D geometry from Inventor to ANSYS design modeler to create the "interface" that is separating the hexahedral mesh and tetrahedral mesh, and create the domain of my simulation.
2. I imported those geometry to ICEM CFD to create parts and built topology to intersect the surface parts of the "interface" with my train model.
3. Generated hexa mesh for the upper parts of the train by splitting the block, and associating them (vertex to point, edge to curve, surface).
4. Next I deleted the blocks under the train (inside the "interface") for it's going to be meshed using tetra mesh.
5. Set up global mesh set up scale to 1.0, curvature proximity not enabled yet, and set the size of part mesh set up to 0.08 (image attaced). I Inserted material point, generate those tetra mesh using robust octree, and smooth it using laplace and without the laplace.
6. Last, I merged the hexa and tetra mesh by using edit mesh>merge mesh.

Merging those two mesh results an error message such as:
could not include quad, error including edge, and "I am trying to include edge but vertex isn't even in the region 1, error including edge, unable to remove prism node. orphans could not be removed.

Despite such error, the mesh was able to be exported and read in ANSYS Fluent. I could initialize the flow, and calculate it, but the residual doesn't seem to be going down. And the contours resulting from the calculation doesn't show something important.

What I think:
I suspected that the problem is caused by poor quality of tetra mesh of the underbody parts, and the merging of hexa and tetra.

Does anyone know how to resolve the merging problem?
How should I improve the tetra quality of the mesh?
Is it correct if I use interior boundary condition for the "interface" part of my mesh? (the yellow surface in pict below)

Thanks in advance.
Best regards,
Attached Images
File Type: png train 3D model with interface.png (24.2 KB, 19 views)
File Type: png train 3D model without interface.png (32.0 KB, 13 views)
File Type: png train hexa mesh upper part and outer interface.png (63.0 KB, 17 views)
File Type: png train tetra mesh underbody.png (77.0 KB, 15 views)
File Type: png merged mesh.png (92.7 KB, 20 views)
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external aerdynamics, hybrid mesh in icem

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