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Residuals not converging, but staying stable and fluctuating

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Old   February 26, 2021, 04:19
Default Residuals not converging, but staying stable and fluctuating
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Ash
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Hi,
I am doing a hypersonic flow simulation on re-entry spacecraft, and for some reason, my residuals don't converge but rather stay stable for a while and then fluctuate (attached is a picture of it). I understand that the fluctuations could be decreased using relaxation factors, but could someone explain to me why the continuity and other variables aren't converging, as I would expect some sort of convergence after Would it be something to do with the mesh or initial BCS
Thanks
Residual 1.JPG

Residual 2.JPG

Residual 3.JPG
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Old   February 26, 2021, 06:26
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Sayan Bhattacharjee
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Do you have a fluctuating von-karman vortex street in the wake region?
Transient phenomenons cause fluctuations in residuals.


You can run the simulations more 10000 iterations *here*, and see if the residuals converge or keep fluctuating. If they keep fluctuating but don't diverge, the solution might be okay.
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Old   March 3, 2021, 02:48
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Ah I see thank you. I do notice Von-Karman Vortex sheets, and the results do look quite similar to the expected values. I have noticed though that my meshing is quite inconsistent, on of the blocks in a multi block grid. Do you think thatwould also have an effect?
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Old   March 3, 2021, 11:40
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Quote:
Originally Posted by ashf9 View Post
Ah I see thank you. I do notice Von-Karman Vortex sheets, and the results do look quite similar to the expected values. I have noticed though that my meshing is quite inconsistent, on of the blocks in a multi block grid. Do you think thatwould also have an effect?
Hello,

Could you post a photo of the 'inconsistent' meshing?
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Old   March 3, 2021, 15:13
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Sure, I've attached some photos of the mesh. For some reason, Ansys won't let me use the edge sizing for one block of my grid, and I can't seem to find out why.
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Originally Posted by aero_head View Post
Hello,

Could you post a photo of the 'inconsistent' meshing?
Attached Images
File Type: jpg Close Up Grid.JPG (40.5 KB, 6 views)
File Type: jpg Multi Block Grid.JPG (141.2 KB, 6 views)
File Type: jpg After Edge Sizing.jpg (115.0 KB, 7 views)
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