Hi I made the 28^3 computation without filter and all results are plotted together. The KE is well predicted even on the coarse mesh. The dissipation rate did not seem to change much with/without filtering on 28^3 mesh. I will try with more elements to see if the results improve and compare with Brachet et al. Thanks praveen On Sun, Dec 9, 2012 at 9:45 PM, <[email protected]> wrote:
Hi Praveen
Filtering removes energy at the small scales (small length scales/high frequency components) If you estimate the turbulent kinetic energy removed by the filtering and compare it to the resolved kinetic energy or the total (resolved+subgrid scale) then your simulation :
(1) May be considered DNS ; if the above ratio is small (2) LES if it is relatively big
in (2) the hope is that subgrid scale motion does not affect the scales of interest in a given problem.
Filtering stabilizes simulations since it provides a way for removing energy at the small unresolved scales. I ran turbulent wake simulations in the past where filtering was absolutely necessary and the argument was that it did not affect the scales of interest.
So the bottomline is you need to at least be aware of what scales are impacted by filtering and if indeed you are interested in such scales. That is why you see some comparisons in the paper for a given case with different values of the filtering parameter.
so let me know what happens when 32^3 is run with f=0 and also the comparison to Brachet et al.
Ammar
This is impressive to me! the fact that filtering is not contributing too much to the dissipation rate and that both the trend/time evolution and numerical magnitude of the dissipation rate are accurately predicted throughout the simulation. Ammar On Dec 12, 2012, at 5:02 AM, [email protected] wrote:
Hi I made the 28^3 computation without filter and all results are plotted together. The KE is well predicted even on the coarse mesh. The dissipation rate did not seem to change much with/without filtering on 28^3 mesh. I will try with more elements to see if the results improve and compare with Brachet et al. Thanks praveen
On Sun, Dec 9, 2012 at 9:45 PM, <[email protected]> wrote: Hi Praveen
Filtering removes energy at the small scales (small length scales/high frequency components) If you estimate the turbulent kinetic energy removed by the filtering and compare it to the resolved kinetic energy or the total (resolved+subgrid scale) then your simulation :
(1) May be considered DNS ; if the above ratio is small (2) LES if it is relatively big
in (2) the hope is that subgrid scale motion does not affect the scales of interest in a given problem.
Filtering stabilizes simulations since it provides a way for removing energy at the small unresolved scales. I ran turbulent wake simulations in the past where filtering was absolutely necessary and the argument was that it did not affect the scales of interest.
So the bottomline is you need to at least be aware of what scales are impacted by filtering and if indeed you are interested in such scales. That is why you see some comparisons in the paper for a given case with different values of the filtering parameter.
so let me know what happens when 32^3 is run with f=0 and also the comparison to Brachet et al.
Ammar
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