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[FLOEFD]-2D Calculation from 3D

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Old   February 28, 2018, 06:35
Default [FLOEFD]-2D Calculation from 3D
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Maxime Perelli
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Hello,
Is there a tutorial or some material which explains how to handle a 3D Geometry in a 2D Calculation.
For instance I have a flow in a 3d pipe and I want to calculate it in 2D.
Perfectly would be axisymetrical...
Thanks for any tipp
Maxime
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Old   March 28, 2018, 08:17
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Hi Maxime,

There is a drag tutorial with a 2D project but it is not the inside of a pipe.

In principle, you can use a flat plate for the pipe walls except if the curvature is of importance, if the domain is thin enough like a 2D slice, there wouldn't be any information on its curvature as well. So this is a possibility. You can use either two walls for both sides of the pipe or you use one wall and model the centerline as symmetry as it would be just a mirrored flow anyway.

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Old   April 9, 2018, 02:52
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Hello Boris,
I was able to run my model in 2D, but it was not so easy as in 3D.
Indeed I had to create the 2d sketch from scratch.
I thought FloEFD has capability to recognize a 2d "section", from a 3d model
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Old   April 9, 2018, 04:01
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FloEFD's 2D is at least 1 cell thick (basic mesh) when it refines it still applies the octree refinement so not only in 2D but also in 3D but Level 0 cells are 1 cell in thickness. So if you go into the computational domain settings you will be able to set the 3rd dimension thickness for the computational domain. So you could basically set a 2mm thickness and then have the cell size in the other directions 1 cm in length, the thickness will be 2mm.

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Old   April 9, 2018, 10:02
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Maxime Perelli
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Hello Boris,
My issue wasn't on the mesh side, but more on the topology.
FloEFD couldn't switch automatically from 3d to 2d without "preparing" the topoly
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Old   April 9, 2018, 10:25
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Oh, yes. The preparing model phase in the mesher is the process of writing the CAD geometry out for the mesher to process it. This has to be done as soon as the geometry or the computational domain changes as this is what is used by the mesher and the geometry in the computational domain is being prepared for the mesher.

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Old   April 10, 2018, 02:14
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Maxime Perelli
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So my (implicit) question was: can we easy switch from 3d to 2d.
Let's take the geometry of tutorial Heat Exchanger Efficiency (3d).
Can we handle it in 2d in few steps?
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Old   April 10, 2018, 04:16
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In principle yes.
I think the center hot pipe has a velocity applied which works in 2D as well, the other cold inlet has a volume flow rate I think so this has to change as the volume flow rate is based on a smaller surface due to the thin 2D inlet piece.

But the issue is more than the center pipe is splitting the top part where the cold fluid enters and leaves from the bottom part of that fluid volume as there is no way the fluid can flow around the center pipe in a 2D slice.
Therefore the simulation will not provide correct results as the flow is a 3D flow for the heat exchanger but the switching the model can be done easily.
Of course, it always depends a little on the model and adjustments that need to me done on the boundary conditions mentioned above or if a geometry does not 100% satisfy the 2D consideration approach FloEFD uses, such as cone with a pointy tip where the tip becomes a single point but FloEFD uses a, well semi-2D approach, so not an actual 2D slice but a 2D with one cell thickness etc. but in general yes.

See my images attached.

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Old   April 10, 2018, 10:20
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Maxime Perelli
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OK it seems to be easy.
I tried for weeks ago, but I couldnt switch from 3d to 2d.
Perhaps because I started from an "already computed" 3d model, and not from scratch...
Anyway thanks Boris for your info
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Old   April 10, 2018, 10:45
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It still is easy to do. You will need to adjust the boundary conditions and make sure that you run from scratch including meshing of course, not continue the calculation.
What you can do with such changes is to simply create a clone with all the settings and then edit that clone for a 2D case. If you have goals of BCs outside the 2D computational domain they will complain either delete them completely of if just some surfaces are outside, use the filter option to filter out the surfaces laying outside the computational domain.

This should work.

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Boris
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