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July 31, 2021, 13:48 |
Aliasing low frequency in Energy Spectrum
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#1 |
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Join Date: Feb 2021
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Hi,
I am running a case in a CFD LES software with implicit filter. Have you ever experienced an aliasing due to the grid? The spectra in frequency with a coarser grid seems to have bigger value of energy then the same case with a finer grid. Can this be due to an aliasing caused by the grid? |
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July 31, 2021, 15:47 |
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#2 | |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
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Quote:
It could be an effect of aliasing (but what about your discretization of the non-linear terms?) but that could be one among other possible causes. Could you provide details of your simulation and post the figures of the two spectra? |
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July 31, 2021, 17:04 |
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#3 |
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If I have an aliasing, is it possible that some terms that should have been counted as sub-grid scales, are instead counted in the lower frequency?
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July 31, 2021, 17:10 |
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#4 | |
Senior Member
Filippo Maria Denaro
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Quote:
Aliasing means that the non-linear quadratic terms produce components behind the cut-off grid frequency, that is in the range of the unresolved terms. But do not forget that the SGS model by itself acts adding a contribution only on the lower resolved frequencies. Thus, also some problems in the SGS model could generate an increasing in the resolved energy level. Without details I cannot say more. |
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August 12, 2021, 04:48 |
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#5 |
Member
EM
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u r probably using finite differences which means aliasing from high wavenumbers is not an issue. also, the unpredictability of low resolution simulations based on truncation error for stabilization means that u must increase resolution 'sufficiently' before start considering fanciful alternatives.
also, yr domain may be too short but u have given shod-all info on yr simulation. -- |
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August 12, 2021, 05:18 |
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#6 | |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
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Quote:
"using finite differences which means aliasing from high wavenumbers is not an issue" why do you wrote that? |
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