Hi,
Please can I have suggestions of articles and publications devoted for comparing LES results from those obtained by a DNS.
I have all the required statistical fields (all terms appearing in the RANS and FANS equations, in addition to the TKE and Reynolds Stress equations). I would like basically to estimate, numerically, a turbulent viscosity (scalar) from the tensors...
Best Regards
At a first glance, one can directly compare averaged profiiles, spectra, r.m.s. between LES and DNS solutions, like we did here
https://www.researchgate.net/publication/313851712_A_comparative_test_for_assessing_the_performances_of_large-eddy_simulation_codes?_iepl%5BviewId%5D=ZiXF8i3jmGHzas1v0ZIasCKn&_iepl%5BprofilePublicationItemVariant%5D=default&_iepl%5Bcontexts%5D%5B0%5D=prfpi&_iepl%5BtargetEntityId%5D=PB%3A313851712&_iepl%5BinteractionType%5D=publicationTitle
A more careful comparison could include the fact that the LES solution expresses a filtered field so that one can think to filter the DNS data with a filter that mimics that used in the LES solution. This is only a static application to the solution but can be somehow useful.
You can have a look to sec. 4.2 here https://www.researchgate.net/publication/227233758_A_new_development_of_the_dynamic_procedure_in_large-eddy_simulation_based_on_a_Finite_Volume_integral_approach_Application_to_stratified_turbulence
Conference Paper A comparative test for assessing the performances of large-e...
Article A new development of the dynamic procedure in large-eddy sim...
Hi Fillipo,
Thanks for these interesting articles.
So I see that the turbulent viscosity is estimated from the DNS by the Boussinesq eddy viscosity model, basically an error minimization principle.
This ensure that the turbulent viscosity is a scalar, as far as the right hand side contains only tensors.
BR
Elie
Dear Elie
yes, given a DNS solution you first have to apply on the field a filter that mimics the one in the LES solution. Then you compute the eddy viscosity scalar field according to the definition. Of course, that viscosity field depends on the filter width.
best regards
Filippo
Dear Tapan,
filtering a DNS is not strictly required but it is somehow useful to compare some statistics. But answering to your issue, I can say: yes, using implicit filtering based on FV or FD you have the action of the filtering also on the resolved scales, before the Nyquist cut-off of the LES solution. You can see that by looking at the transfer functions induced by the discretization. That does not affect the basic premise of LES as it depends on the shape of the adopted filter. I agree with you only for the spectral cut-off filter (projectiv filter) that, in principle, capture all the resolved scale without smoothing.
If you are interested to this aspect of LES, you could find more details here:
https://www.researchgate.net/publication/220206317_What_does_Finite_Volume-based_implicit_filtering_really_resolve_in_Large-Eddy_Simulations
Article What does Finite Volume-based implicit filtering really reso...
Yes, I am aware ;-) I also worked and proposed some approach for LES using upwind.
But I think that in the LES community there are different schools that approach the LES equations in two ways, as either real filtered PDEs or numerical unresolved (by the discretization of equations and domain) equations. In my paper I tried to express my idea about those differences. I think that expecially the FV approach for LES was quite misunderstood.
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