March 2016 - Nektar-users - imperial.ac.uk

Re: [Nektar-users] Implicit LES in Nektar++
by Rodrigo Moura 01 Mar '16

01 Mar '16

Dear Kamil, For the incompressible solver you should definitely include the dealiasing flag, namely, <I PROPERTY="SpectralhpDealiasing" VALUE="True" /> inside section <SOLVERINFO> of your XML file. Please refer to Sec 2.4.1.2 of Spencer's book (Spectral/hp element methods for computational fluid dynamics) for an explanation about the dealiasing strategy used by the incompressible solver. Note however the following. The success of our implicit LES approach via high-order CG methods (both in terms of discretization robustness and solution quality) is closely connect to a sensible use of SVV (spectral vanishing viscosity). This requires good knowledge of turbulence physics and of LES-like approaches and takes some programming expertise in Nektar++ since currently we do not have full control of the SVV operator only through the XML file. What I mean is that, for the purpose of implicit LES, you might need to modify the SVV operator inside Nektar and this is a somewhat advanced topic not covered by the user guide, as the CG+SVV-based implicit LES is a modern approach and not yet fully mature. Please note the following study that discusses the behaviour of different SVV operators from a perspective of under-resolved turbulence computations: http://www.sciencedirect.com/science/article/pii/S0021999115008256 Cheers, Rodrigo . On Mon, Feb 29, 2016 at 11:22 AM, Kamil ÖZDEN <kamil.ozden.me(a)gmail.com> wrote: > Hi Rodrigo, > > Thanks for your interest at first. I want to use the incompressible one. > Do you know what settings should I do in the *.xml file to run an implicit > LES? > > Best Regards, > Kamil > > 29.02.2016 12:03 tarihinde Rodrigo Moura yazdı: > > Hi Kamil, >> >> Do you intend to use the incompressible solver or the compressible one? >> The incompressible is currently much more efficient in Nektar due to the >> possibility of using implicit time-stepping. >> >> Cheers, >> Rodrigo >> . >> > > > --- > Bu e-posta virüslere karşı Avast antivirüs yazılımı tarafından kontrol > edilmiştir. > https://www.avast.com/antivirus > >

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Porous Region in nektar++
by 张宾 01 Mar '16

01 Mar '16

Dear all We are using nektar to calculate multiple outlets flow problem, and porous region is required in the simulation. In my opinion, when the porous region is applied in computational domain, inertial resistance coefficients and viscous resistance coefficients should be set for the porous region. Is there any instructions that tell us how to set these two coefficients in Condition section of XML session file, or are there other ways to use porous region in nektar++? Best regards, Bin

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How to figure out each Face's Expansion Coefficients given ElementExpansion Coeffcients
by ashok jallepalli 01 Mar '16

01 Mar '16

Dear All, I am trying to do the following in my code. I am stuck with not being able to few steps. Can you please suggest if there are any api calls which I can use. Or areas of code which does the same. Take Multi-region element, Loop through each element in the multi region. Loop through each face of element of multi region. Get 2D element expansion of each face and its coefficients. End each face loop. End each element loop. Question(1) To get the 2D element expansion, I am able to use GetfaceExp() on Expansion3D. This only works for boundary elements when the field is Cont3DExp. When element is not in the boundary it gives a segmentation fault 11. - Is this supposed to work ? Question(2) I can overcome the above problem by initializing the field as DisCont3DExp, while loading from fld file. (This seems to work for now). - Is there a function to get each face's Expansion coefficients from element expansion coefficients ? - Or should I dynamically check if the element is Hex, Tet, prism and try to figure out from the mapping order? Thank you,

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