# LESDES deltas

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 January 13, 2009, 08:18 Thank you very much, Markus. #21 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 Sponsored Links Thank you very much, Markus. What is Turbulence Special Interest Group, and where is it, may I ask? __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

 January 13, 2009, 10:14 Hi Markus, What about usin #22 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 Hi Markus, What about using a camera instead of a scanner? I think it would be fine. I use camera for many times and I see the papers look okay. Regards, Daniel __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

 February 13, 2009, 09:39 Hi, @ Markus: yes, the grad #23 Senior Member   Fabian Braennstroem Join Date: Mar 2009 Posts: 407 Rep Power: 12 Hi, @ Markus: yes, the gradient idea is not really working... For the SST model, one simple switching condition could be y*=y*sqrt(k)/nu volScalarField S = sqrt(2.0) * mag(symm(fvc::grad(U_))); volScalarField Ssgs = sqrt(2*S*S); volScalarField nuSGS=sqr(Cs_*delta()) * Ssgs; yStar=y_*sqrt(k_)/nu(); f_=((tanh(0.01*(yStar-500.0)))+1)/2; volScalarField nuT=(a1_*k_/max(a1_*omega_, F2()*sqrt(S2))); nut_ = (1-f_)*nuT + (f_)* min(nuSGS,nuT); Could this work for you? About the SIG, you can a little bit on: http://openfoamwiki.net/index.php/Sig_Turbulence Regards! Fabian

 February 17, 2009, 06:15 Hi Fabian, I like the fact, #24 Member   Markus Weinmann Join Date: Mar 2009 Location: Stuttgart, Germany Posts: 77 Rep Power: 10 Hi Fabian, I like the fact, that switching the model equations gives you well defined models for the LES and RANS part. Eventhough, the Smagorinski Sgs model is probably not the best choice. If you would just switch the length scale, as in the DES approach, it is arguable whether the RANS model performs well as a Sgs model (I guess it does not). Having a properly defined SGS and RANS model seems very appealing to me. However, I am not really sure what the most consistent hybrid formulation would look like. For the moment, I haven't decided which method I am going to use. Regards Markus

 February 17, 2009, 10:45 Hi Markus, As a DES user, I #25 Member   Philippe B. Vincent Join Date: Mar 2009 Location: Quebec, Canada Posts: 32 Rep Power: 10 Hi Markus, As a DES user, I found very useful the use of the DDES implementation. I suggest you consider it for the hybrid formulation to choose. Of course, it was well suited for my application and might not be for yours, but it definitely helps to prevent the switch from RANS to LES inside the boundary layer. Regards, Philippe

 February 24, 2009, 04:53 Hi dear friends, I made a s #26 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 Hi dear friends, I made a simple DDES implementation, and not sure if it works. Do you have any idea and experience in using DDES? Howto check it? Anyway, I am working on channelFlow to see if it works better than DES as a wall function. The 2nd question is in S-A model: ----------
volScalarField r = min      (          nuTilda_         /(             max(Stilda, dimensionedScalar("SMALL", Stilda.dimensions(), SMALL))            *sqr(kappa_*dTilda_)          ),          scalar(10.0)      );
----------- But why r's limit is 10.0? I have set my rd (let you understand) in DDES no larger than 1.0 (Please correct me if I was wrong) so, any ideas? Daniel WEI __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

 February 24, 2009, 10:40 Good morning Daniel, I hope yo #27 Member   Philippe B. Vincent Join Date: Mar 2009 Location: Quebec, Canada Posts: 32 Rep Power: 10 Good morning Daniel, I hope you're doing fine! My DDES implementation does not limit the value of rd. Maybe it would be a better practice to do it but the tests I made so far look good for the values of rd and fd. The picture above shows those values in the ERCOFTAC conical diffuser (attached B.L.). I have very little experience in channelFlow, but I guess you can get better results with DDES if you use fine grids. To check your implementation, I suggest you refine your mesh a few times to see the effect. Then you can plot rd and fd to see if they make sense. I would be very interested to see some of your results! Keep us posted and good luck, Philippe

 February 24, 2009, 11:13 My openSUSE is broken, So I sp #28 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 My openSUSE is broken, So I spent a whole afternoon reinstall the OpenSUSE-11.1. I'll get OpenFOAM work tomorrow. Because of the Spring Festival, I have been delayed for a whole month. In Fact, "Your Image IS NOT Here". "Refine the mesh"? Is it a good idea to do that? As far as I remember what Spalart said before, DES is not always show consistency with grid refining. You did not limit the value of rd? Will it be larger than 1.0 some places? So far in channelFlow, I have saw a very very thin layer near the wall, both in fd and rd fields. The changes are really "steep" near the wall, just as what has been expected. I will do postChannel these days. It's very nice to see your progress, I am very interested too to see your results! Happy day! DW __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

 February 24, 2009, 13:25 Dear Daniel, I hope you enjoye #29 Member   Philippe B. Vincent Join Date: Mar 2009 Location: Quebec, Canada Posts: 32 Rep Power: 10 Dear Daniel, I hope you enjoyed the Spring Festival, even if you were delayed in your work;) I'll try again for the image : The way I see it, DDES is just meant to "protect" the boundary layer from LES mode. It forces the RANS formulation to stay active as long as fd=0. So the point of implementing it is to use what Spalart calls "ambiguous spacings" in the wall parallel direction. So to answer your question, I think that yes it is a good idea to refine the mesh and see the effect because that's the purpose of DDES. As for rd, I'm pretty sure you don't have to limit it because of the definition of fd : fd = 1-tanh([8rd]3) which automatically limits the right hand side to 1. fd is then between 0 and 1 as expected. Regards, Philippe

 February 24, 2009, 14:05 Thank you, you're right! You #30 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 Thank you, you're right! Your Image IS NOT Here again Good night, Philippe! __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

 February 24, 2009, 14:08 http://www.cfd-online.com/Open #31 Member   Philippe B. Vincent Join Date: Mar 2009 Location: Quebec, Canada Posts: 32 Rep Power: 10

 February 24, 2009, 14:13 http://www.cfd-online.com/Open #32 Member   Philippe B. Vincent Join Date: Mar 2009 Location: Quebec, Canada Posts: 32 Rep Power: 10

 February 24, 2009, 14:16 Can't do it sorry. I'll send y #33 Member   Philippe B. Vincent Join Date: Mar 2009 Location: Quebec, Canada Posts: 32 Rep Power: 10 Can't do it sorry. I'll send you an email Bye

 April 12, 2009, 05:42 #34 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 Hello, fomers, where are you now, long time no discussion, How's everything？ What did you guys use DES work for? And what's going on with maxDelta implementation? Daniel __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

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