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[DesignModeler] Problems with flow in a "Pipe within a pipe" problem

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Old   September 24, 2013, 20:47
Default Problems with flow in a "Pipe within a pipe" problem
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Dear Readers,

I am currently in the process of setting up a model in ANSYS/FLUENT of a combustor tunnel. I am relatively new when it comes to creating my own geometries, and thus I have some problems in defining my problem correctly in DesignModeler.

So, the issue is that I have a small portion of the combustor tunnel where I am dealing with three different pipes. One pipe for fuel, one for primary air and one for secondary air. They are presented in ascending order from the center of the enclosure.

In DesignModeler I first created the secondary air pipe with full radius (4"). I extruded this pipe with "Add Material". After that I created the primary air pipe with its proper radius (1.75"). I extruded this pipe with "Slice Material". After that I created the fuel pipe with its proper radius (1/4"). I extruded the pipe with "Slice Material". Lastly, I created the actual Burner Throat where all the three pipes join together. In the extrusion I chose "Add Frozen" for this one (I can't motivate why, as I though Add Material / Add Frozen would have the same meaning in this case?).

However, when I'm running a trial simulation in FLUENT I note that the streamlines from the primary air and the fuel pipe ends where the extrusions ends i DM. For the secondary air pipe the stream will go all the way to the pressure outlet at the exit of the burner throat.

I went back to DM and checked "merge" and "connect", although I believe it's not the proper tools to use in this case as it deals with edges? The problem should be that the "faces" where the Burner Throat and the fuel / primary air pipes intersects are blocked for some reason.

Does anyone know how I should do this in order to get the inner pipes to interact with the Burner Throat?


Thanks for the help!
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Old   September 24, 2013, 23:17
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So this is how the streamlines look like. I also tried to define the exit of the fuel pipe as a pressure-outlet and the exit of the primary air pipe as a pressure-outlet, just to make sure that FLUENT doesn't treat that as a wall. However, I still get the same result. The streamlines hits an "invisible" wall in the inner pipes, for some reason.

Help anybody?! :/
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File Type: jpg DM_Problem2.jpg (87.6 KB, 7 views)
File Type: jpg DM_Problem3.jpg (93.9 KB, 10 views)
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Old   September 25, 2013, 01:15
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By the picture you provided, I can guide you that the inner pipe and main pipe are not merge each other, may be u get the wall between the inner pipe and outer pipe by that the streamlines are stopping at one surface, zoom the wireframe model and check the two edges or in fluent you can check the walls, Best way you can slice the model towards outlet, or unite all and you can create.
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Old   September 25, 2013, 03:55
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Thanks for the help!

I was able to look at the wireframe in the Mesh, and it appears to be a blocking for the inner pipe at the inlet to the combustion chamber. I could also see in FLUENT that a wall was added, which is why the streamline is getting blocked at the inner pipe.

How can I actually get rid of that wall/face that is obviously blocking the entrance? I tried to delete that in FLUENT (without success though, as the stream still would get blocked) I also tried Face-delete in Geometry as well as Slice by face. None of that would work either.

I am actually confused. Is it not possible to have two separate parts for the same simulation in Ansys/FLUENT? It should be very basic, I don't see why it wouldn't work. I need to have two separate parts so that I can make the inner pipe rotate with frame motion.

Let me refine my question. How do I make sure, in DesignModeler, that two separate parts become part of the same flow without one streamline being blocked? I don't want to unite the two parts into one, sole, body.
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Old   September 25, 2013, 04:08
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can you tray with making wall-as interface FLUENT and run...
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Old   September 25, 2013, 04:42
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Hmm sorry, I don't understand what you mean. Although I guess it would work with one body if I could split up the cell zones, so I still could get a moving frame.

I found this: http://aerojet.engr.ucdavis.edu/flue...ug/node192.htm

But I don't think they are clear on how to actually split one cell zone to another. But that'd help if I could do that. Do you have any experience in splitting cell zones vidyanad?

Thanks for the help by the way! I appreaciate that for sure
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