Streamlines problem

Hello friends. I am learning how to operate with the software. My problem is that I can't seem to understand how to generate proper streamlines. Mine just go trough to the surface of any geometry I import. They look like this:

And I need them to look like this:

Please explain what I am doing wrong. None of the available tutorials seems to help me.

Subtract your object from the surrounding volume

You need to create a water tight flow volume. Typically you need to subtract your object from the enclosing volume as described at "CFD Flow Volumes and Solid Models."

If you are going to use a membrane (double sided face) then review the tutorial "Double-Sided Membrane."

Next up you'll need to review your accuracy settings and streamline seed creation. For more details see the tutorial "Incompressible Flow Through a Pipe into a Box."


So far so good. Your clarification helped a lot. However, with a specific obj model i can't seem to manage to do it. It is created in SketchUp, I export it as obj then even if i follow all the steps I can't get the streamlines to not go trough it. Is it because it is not water tight? I tried defining all the faces as "double-sided" but then the solver stops at the 20th iteration with an error.

Learn CFD through tutorials

If your objective is to learn CFD then I suggest you first perform a selection of tutorials, which are specially configured to give you a taste of CFD and how to perform CFD simulations using Caedium. Note each tutorial creates a Residual Monitor, which is missing from your simulation.

I suggest you at least try:

SketchUp models often have problems whereby the faces do not stitch to form a water tight volume for subtraction from a surrounding volume. Double-sided faces are only for membranes that do not intersect any other faces. For more background see "5 Tips for CFD Flow Volume Creation."

The basic premise for all CFD simulation in Caedium is that the flow volume (solid model) represents the fluid around your object.

Simple geometry

Here is my problem. I am able to work perfectly with the builder in Caedium. But if I try importing simple geometry such as a box or a sphere from Autocad or SketchUp, I just can't achieve the same result as the native builder. I have done all the tutorials so far. It seems my problem is that I just can't work with non-native geometry. I know it is something simple that I am missing. I wonder what is it. Thank you for all your help so far.

Stitch Volume with Topology Only enabled

If you are going to use faceted geometry as opposed to analytic geometry then after you've imported your file you will need to use the Volumes->Stitch tool on the Geometry Tool Palette with Topology Only enabled to form a water tight volume - this assumes that all the faces are connected to only one other face through each edge (manifold geometry). From there onwards you have to use the Topology Only option for all your Booleans.

With analytic geometry (typically from CAD systems and using STEP to exchange geometry) there are no restrictions. For more on geometry definitions see "Geometry Exchange."


Giving it a try now. I think that is the problem.

No intersections or overlaps for Topology Only Booleans

When you use Booleans with the Topology Only option the geometry can not intersect or overlap, so for a cube in a larger cylinder the cube has to be away from all the walls of the cylinder.


I have another little question. When I plot the Cp values and then export them into excel, they have the following format.

Outer Surface XYZ:X -18.7451 -18.7452 ...
Outer Surface Cp 0.8136 0.7900 ...
Inner Surface XYZ:X -18.7451 -18.7452 ...
Inner Surface Cp -1.0516 -1.0383 ...


What if I want to get a net value of the Outer and Inner Surfaces Cp values and then extrapolate the color map in another software like SketchUp for example. How do I use the XYZ:X coordinates?

Node and cell value export

A scenario similar to your requirement is described in the section "Export Results to ixCube 4-10" in the tutorial "Flow Over a Double-Sided Membrane."

You'll want to make sure only the flat shaded triangles you want in the OBJ file are visible.

The OBJ export mimics the view of your model as configured in the view window. E.g., if you only have edges visible then that's all that will be exported.

The OBJ polygons exported from Caedium will be different from the original imported polygons.

The Cp CSV data (node values) are ordered in the same manner as the OBJ nodes that define the polygons. The XYZ:X in the the CSV file is redundant for your needs.

Alternatively you could apply Cp to your object's faces (cell values) and then flat shade those faces to view individual triangle colors and export that as OBJ where the MTL file will contain the color attributes.

For more on mesh shading see "View a Mesh." The only difference is that you need to set the Transparent property to off.

Smooth shading will segment (cut) the polygons according to the scalar contour boundaries.

I see. It all worked fine.

I see. It all worked fine. However if I want to use a net value (Cp Outer - Cp Inner = Cp Net) is there a way to visualize it and/or plot it and export it in csv?

2-sided faces for membranes

If you have specified a membrane as 2-sided and applied the Conditions->Wall to both sides then when you export Cp values for each side you can perform the subtraction in your spreadsheet - Caedium does not support face to face result creation.

This will only work for 2-sided faces (resulting in a regular face and a shadow face) where the node ordering (and therefore the CSV) for both sides is the same.


It works brilliantly. I love your software. Thanks for the lesson.