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July 9, 2013, 07:00 

#21 
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Lev
Join Date: Dec 2010
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initial conditions were U=0,p=0. And then flow developed to the "quasi steady state" of turbulence flow.


March 3, 2014, 21:08 

#22 
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Huang Xianbei
Join Date: Sep 2013
Location: CAU,China
Posts: 283
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Hi
I just follow your idea of adding a source term representing the grad(p) in the UEqn, I made my domain as 12.56*2*6.28m in 3 orientation. The fluid is water whose nu =1e6m2/s, the grad(p)=3.8e8m/s2, however, the solution turns to be strange that the residual of Uy,Uz and p increase after a certain timesteps, the residual of p approches about 0.5. Also, the velocity along the y direction increases steadily along timestep, so the solution can converge, what may be the problem? My grid is 64*128*64 

March 6, 2014, 22:27 

#23 
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Huang Xianbei
Join Date: Sep 2013
Location: CAU,China
Posts: 283
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Hi,lev:
Another question(probably very simple). In the controlDict in your test case, the application name is solver_DNS, while the solver you defined is ico_DNS, is this should be "ico_DNS' insteady? 

March 25, 2014, 21:21 

#24 
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Huang Xianbei
Join Date: Sep 2013
Location: CAU,China
Posts: 283
Rep Power: 6 
Hi:
I use the perturbU to make a initial field, setting the maximum streak to be at y+=12 by modifying the perturbU.C. However, the solution takes long time to reach a perhaps fully developed flow after 40000s, also ,the result is not good, as you can see the velocity is higher than the loglaw when y+>30, I don't know how to generate a more proper initial field, can anyone help? 

July 9, 2014, 15:11 

#25 
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Kent Wardle
Join Date: Mar 2009
Location: Illinois, USA
Posts: 208
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Any chance someone can repost the files for ico_dns solver? I am unable to get them from sendspace.
~ EDIT ~ Never mind. I got it now. Thanks for sharing. Last edited by kwardle; July 10, 2014 at 10:59. 

July 6, 2015, 16:46 
Same set up calculation using icoFoam

#26 
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Roro Wang
Join Date: Mar 2010
Location: Cambridge, MA, USA
Posts: 30
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Hi Lev,
Your work looks very amazing. Thanks for the contribution. I tried to use icoFoam directly to reproduce your work but found the mean velocity profile is ok, but the u_rms is much off. So I guess it's due to your modification to the original icoFoam. I noticed you modified the pressure term. Could you explain why and is there any reference to your modification? Update: Got the reason, i.e. the modification applied a constant pressure gradient. Everything works great now. Thanks a lot. foamWang Last edited by foamWang; July 6, 2015 at 23:49. 

November 10, 2015, 09:39 

#27  
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Join Date: Oct 2015
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Quote:
I am trying to compile your solver for OpenFOAM v2.3.0 and of course, it does not work! I tried to make changes to your source code to correspond to the new OF version but it did not work. I am trying to simulate a DNS channel case with a step and want to run my simulations parallelly. If a newer version of your solver is available, please guide me to it. Or if there is something else available from OpenFOAM (2.3.0 or any later versions) to solve the problem. Thanks, KM Solved  Figured out the changes in the icoFoam solver in the new version of OpenFOAM. Was able to compile with v2.3.0 & v2.4.0 Last edited by Hackerbrucke; December 1, 2015 at 08:59. Reason: Able to compile with newer versions 

January 26, 2016, 08:02 

#28  
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Jean Schuster
Join Date: Jan 2015
Posts: 8
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Hi guys.
I'm trying to compile the solver with the OpenFOAM 3.0.0 in the Ubuntu 14.04 LTS x64 distribution. I have total control over the OpenFOAM instalation directory, but when I try to run the "wmake all" command I got the following error: Quote:


January 29, 2016, 05:08 

#29  
New Member
Join Date: Oct 2015
Posts: 3
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Quote:
The icoFoam solver implementation was improved from the one in OFv2.1.0 due to the restructuring of some libraries. I took the icoFoam code from v2.4.0 and implemented the changes as suggested in the code from Levka. An additional control on the Maximum Courant number was added. I am not sure if it will work with the latest v3.0 because I haven't used it but you can give it a try. Best regards, KM PS: Incase it doesn't work, just take a look at the icoFoam code in v3.0, copy the files, rename the solver and make the changes according to this code. 

January 29, 2016, 10:58 

#30  
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Jean Schuster
Join Date: Jan 2015
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Quote:
I'm starting to work with CFD now, so I still haven't much to add to the comunity. I would like to thank you guys, in special to levka and Hackerbrucke. 

April 13, 2017, 13:14 

#31 
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Aaron
Join Date: Apr 2016
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Hi foamers,
I have some doubt in levka's DNS test case, he compare with kim and moin(1987) Retau=180, and Re=3300 and in levka's case, he set nu=1.5e5, so the mean inlet velocity is U=Re*nu/L=3300*1.5e5/1=0.0495, but in his case, he set the mean inlet velocity U=0.045 I compare his result with moin, the uplus_mean and urms show a good agreement, and I calculate the case's Utau=0.00263842, it approximate to Utau=Retau*nu/h=180*1.5e5/1=0.0027 however, I run a case with mean inlet velocity U=0.0495, when I check my result, my Utau=0.00306223, uplus_mean can fit with moin, but my urms are some bigger than moin's result can someone good at DNS explain it to me? Best regards Last edited by Aaron_L; April 14, 2017 at 00:38. 

April 14, 2017, 02:04 

#32 
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Santiago Lopez Castano
Join Date: Nov 2012
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Low order codes generate higher dissipation. This due to the use of discrete CDS approximations. A simple Fourier analysis reveal the 'dampening' of waves passed through low order gradient schemes. See this DNS not in the context of Kim&Moin, who used spectral codes for their work, but in the context of FVM.
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April 14, 2017, 04:34 

#33  
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Aaron
Join Date: Apr 2016
Posts: 22
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Quote:
but why levka's case (Re=3000) can ensure his case result Retau=176≈180？and his result fit with moin's result well. can you give me some suggestions? increase grid amount, or use high order discretization schemes? or may be in his or my case something set error. Best regards. 

April 14, 2017, 04:55 

#34 
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Santiago Lopez Castano
Join Date: Nov 2012
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To clarify, "Precision" is not the correct word to use in this context, least to talk about the goodness of a particular approach in solving numerically the incompressible NSE; again, it's more appropriate to talk about context: as you should never use an F1 car to drive back from work, you would never compete in F1 using a Fiat Panda, both do the job of taking you places but you use them for completely different reasons. FVM methods used in the context of CFD serve for the study of complex geometry and physics scenarios, where no accurate comparison can be made, and "Better" methods just won't cut it, maybe because it's too slow, too dispersive (thus unstable), or the physics of turbulence too complex that modelling needs to be used. Note that the greatest achievements in incompressible turbulence (algorithms, models, etc) have come from the FVM community, and then somehow transformed and used by the other communities (FEM, Spectral, etc.)
Coming back to your query, I don't know what spatial schemes are you using, but you should avoid all TDV/NVD/limited/corrected schemes when doing DNS as they add dissipation "on purpose". For such a low Reynolds Number, a low order Solver should give you nice results as long you keep the cell Peclet Number under 2 and, obviously, the size of the cells fine enough to resolve the dissipative scales of turbulence for your particular simulation. 

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