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Showing results 1 to 25 of 35 Search took 0.00 seconds. Search: Posts Made By: FMDenaro

Forum: Main CFD Forum November 30, 2016, 05:22

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro well, I was thinking about a 4x4 mesh of size h... well, I was thinking about a 4x4 mesh of size h with values at grid intersection (5x5 values) not at the center of the cells but we can work also on this figure you have done. Consider the nodes...

Forum: Main CFD Forum November 30, 2016, 04:48

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro No You should consider Nyquist theorem and the... No You should consider Nyquist theorem and the simplest 2D example requires a 4x4 grid to be sampled on a 2x2 grid

Forum: Main CFD Forum November 30, 2016, 04:26

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro Just select one node each two somehow similar to... Just select one node each two somehow similar to the multi grid procedure

Forum: Main CFD Forum November 30, 2016, 04:15

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro Interpolation acts as a smoothing ... Try only... Interpolation acts as a smoothing ... Try only the sampling of the nodes

Forum: Main CFD Forum November 30, 2016, 03:53

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro Are you just extracting 64 nodes from the 128... Are you just extracting 64 nodes from the 128 sampling each two cells? Could you post the two spectra superimposed in a unique figure?

Forum: Main CFD Forum November 30, 2016, 03:08

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro In no way the kinetic energy is conserved after... In no way the kinetic energy is conserved after you apply any filter... just think about the sharp cut-off that cut away the content corresponding to the integral (in dk) of the eliminated...

Forum: Main CFD Forum November 29, 2016, 10:37

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro doing that using a spectral method would be very... doing that using a spectral method would be very easy... But as you want to work only in physical space you need to sample data. As you wrote, the initial grid (h=2*pi/128) leads to kc=64. Now,...

Forum: Main CFD Forum November 29, 2016, 10:10

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro there are more issues in what you are doing ....... there are more issues in what you are doing .... First, the computational grid introduces a cut-off at kc=pi/h, then the discretization you use introduces some smoothing for frequencies k<kc. I...

Forum: Main CFD Forum November 29, 2016, 05:25

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro You can adopt a deconvolution procedure to better... You can adopt a deconvolution procedure to better reconstruct the content at high resolved wavenumbers. However, the cut-off is always dictated by the grid resolution. Alternatively, you should...

Forum: Main CFD Forum October 8, 2016, 04:20

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro let us know about your work.... concerning the... let us know about your work.... concerning the Burgers equation analysis, if you want you can follow what we did some years ago in the integral-based formulation:...

Forum: Main CFD Forum October 7, 2016, 05:37

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro Unfortunately the paper is not clear at all in... Unfortunately the paper is not clear at all in the integral formulation...I am not able to see how Eq.(15) represents an explicit filtering application... I suggest to consider the Burgers equation...

Forum: Main CFD Forum October 7, 2016, 05:19

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro Again, you are here considering only the aliasing... Again, you are here considering only the aliasing error due to the quadratic product. The numerical error is due to the local truncation error produced by the discretization of the derivative. The...

Forum: Main CFD Forum October 7, 2016, 05:16

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro The goal of the explicit filtering in LES is to... The goal of the explicit filtering in LES is to produce a "bar" velocity cleaned by numerical errors and provide such field to the action of the SGS model. The key is that one wants that the SGS...

Forum: Main CFD Forum October 7, 2016, 04:43

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro ok, if your bar is the "explicit" filter.... I... ok, if your bar is the "explicit" filter.... I prefer to write the bar and then add if it is implicit (discretization-based) or explicit. [/QUOTE] For me, the computed \overline{u}^{n+1} is...

Forum: Main CFD Forum October 7, 2016, 03:41

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro I think that a key to understand the topic, is... I think that a key to understand the topic, is that the LES equation http://www.cfd-online.com/Forums/vbLatex/img/b9d9114fc91a53a4ec8751a6a697394e-1.gif is not then implemented using an...

Forum: Main CFD Forum October 6, 2016, 17:17

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro Thanks ... I see that this topic is not... Thanks ... I see that this topic is not simple....I had to study, think and re-study papers. I passed many days working on the equations to understand how to write correctly the LES equation in...

Forum: Main CFD Forum October 6, 2016, 17:11

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro I understand that the issue is not simple and I... I understand that the issue is not simple and I will try to explain by using the simple Burgers equation: du/dt + d(u^2/2)/dx = 0 Formally the LES equation is obtained by applying the filter to...

Forum: Main CFD Forum October 6, 2016, 12:13

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro Paolo, the paper of Vreman still do not include a... Paolo, the paper of Vreman still do not include a further explicit filtering on the convective flux but, similarily to what I wrote before, consider only the surface integral as the volume filter....

Forum: Main CFD Forum October 6, 2016, 10:34

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro Yes, you do not apply on the time derivative but... Yes, you do not apply on the time derivative but it results as a consequence of the application of the explicit filtering on the convective term...if you filter the convective flux, what is the...

Forum: Main CFD Forum October 6, 2016, 09:58

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro the issue is much more complex...when you applly... the issue is much more complex...when you applly the filter on the convective terms, you must consider you solve a term like d/dt [u_bar]_expl and this is different if you use the...

Forum: Main CFD Forum October 6, 2016, 08:38

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro That means you want to work with 1/|V| Int... That means you want to work with 1/|V| Int [S] n.[v_bar v_bar]_expl dS where [ ]_expl is the explicit volume filtering. Well, this was never used in the literature and deserves much more...

Forum: Main CFD Forum October 6, 2016, 08:14

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro As you can read in that papers, they use the... As you can read in that papers, they use the differential, not the integral formulation. Therefore, they apply the filter on the term Div ( v_bar v_bar) but then, they commute filter and...

Forum: Main CFD Forum October 6, 2016, 08:00

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro I am not sure of what you are doing...if you work... I am not sure of what you are doing...if you work with the FV discretization of the integral form, you get to work with this convective flux term: 1/|V| Int [S] n.v_bar v_bar dS But I want...

Forum: Main CFD Forum April 19, 2016, 03:01

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro right, in the dynamic procedure you work with the... right, in the dynamic procedure you work with the so-called test-filtering...it is necessary to perform a further explicit test-filter having the third Nyquist frequency greater than the other two.

Forum: Main CFD Forum April 4, 2016, 18:56

Replies: 85 Explicit filtering in LES Views: 10,870 Posted By FMDenaro "that the grid used for composing u_i... "that the grid used for composing u_i (bar)u_j(bar) product has to be at least twice as fine" You must think about two concurrent problems, the discrete equation that provides the implicit...

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