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Old   November 25, 2019, 08:48
Default Gaps between Turbine Blade Rows
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Hi everyone,

I have an odd problem with axial gaps in my mesh that I cannot seem to figure out. For work, I am simulating the through-flow within a 6-stage low-pressure turbine with an exit case strut in CFX. I was given flow path geometry and blade profiles at text files of the point sets. I used Siemens NX 10 to produce the 3D blade solids from the text files of spanwise blade profiles. The blade solids extended beyond the flow path until I used the flow path curve to truncate the blade shape. Then, I used the flow path curves to produce sheet bodies of the meridional surfaces for each blade row. I made sure all inlet and outlet curves defining the meridional surfaces were parallel to the x-axis in the image. Essentially, I am only importing the blade solids and the meridional surfaces (see first image)

After I imported the geometry, I made a plane coincident to the xz plane and projected the hub, shroud, inlet, and outlet curves for each blade row. Every blade has a hub and shroud curve. 14 inlet/outlet curves were projected (for example, the curve that is the inlet to the first rotor and outlet of the first stator is one curve, see second image). I used the “FlowPath” function in BladeEditor to create the flow paths for each blade. I choose the “Axial Turbine” machine, correct rotation direction, and defined 17 layers. To complete the geometry, I used the “ExportPoints” function. I left the export type as “TurboGrid” but did not export the curve files. I specified the flowpath, the blade surfaces, number of blades, and blade row.

To produce my mesh, I used TurboGrid. In total, my model as 13 mesh regions (one for each blade). I enabled the blades by editing the properties of the TurboGrid components to reflect the proper blade (see third image). I used the default settings for inlet and outlet domains. After setting my preferred mesh density, I connected all the mesh components into CFX-Pre. This is where the axial gap problem showed up (fourth image). After going through the “Turbo Mode” set up and checking the automatic boundary conditions, I cannot find the source of this issue. The boundary type is set to “Interface” with “Conservative Interface Flux” for all the boundary detail options, non-overlap conditions are deselected, and there are no boundary sources.

I tried to be as thorough as possible in my explanation of my set up. I am confident the issue is not in DesignModeler since the gaps do not show up until CFX-Pre. I believe the issue is within my set up in TurboGrid or CFX-Pre. I have attempted to mitigate this issue by several ways:

- Establishing only 14 inlet/outlet curves in DesignModeler (instead of each blade row having an inlet and outlet for a total of 26 curves)
- Making the inlet/outlet curves parallel to the x-axis shown in the first image
- Applying Connectivity between interfaces in CFX-Pre
- Turning off inlet and exit domains in TurboGrid
- Trying different geometry import file types (.prt, .stp (203), and .iges)
- Finally, I have searched online for answers to no avail

Any help would be greatly appreciated and thank you for reading
Attached Images
File Type: png geomtryimport.png (68.2 KB, 20 views)
File Type: png curve set up.png (96.6 KB, 18 views)
File Type: jpg turbogrid config.jpg (75.4 KB, 14 views)
File Type: png axial gap.png (39.9 KB, 18 views)
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Old   November 26, 2019, 01:22
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Havent used T-Grid in a while but I remember it being a bit restive when defining the inlet/outlet position of the parts. Have you tried to manually set them? I think there was an option to define an axial postion for both hub and shroud for each region. Then you can either manually apply them to the next part or if I remember correctly import it from the previous one. I also remember that there was a strange error message when trying to import it, but I ignored it and it still worked.

Good luck.
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ansys cfx-pre, cfx, turbine, turbogrid, turbomachinery

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