Reply To: the method to create external flow geometry with design modeler

[NickFL]

The error message is a pretty good indicator of what is going wrong here. When you have two cylinders that are tangent to each other, they cannot be combined into a single body because there is a 1D line between them and not a 2D face. Similarly, the fluid volume around them would result in a non-manifold body, as the error message indicates. Physically, there will always be some roughness that makes the contact line irregular. And for fluid flow, there really will not be much flow in this valley region where the two cylinders touch.

Two possible solutions.
1. Move the centerlines closer together so that there is some overlap between the cylinders. This will eliminate the non-manifold body problem that you are experiencing in DesignModeler.
2. And this is probably the better solution, create a thin body that will merge the two bodies together. I would create a small symmetrical rectangular body, only a fraction of a millimeter wide. You can then use this body to merge the two cylinders into one. I might even round the two valleys where they contact depending on why I am simulating this and what the mesh looks like.