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# les-ras
  • k
  • t
    Thank you very much for answering. It will be nice for future reference since I plan to use kOmegaSSTIDDES also, but I forgot to mention that its was for SpalartAlamarasIDDES....sorry my bad....but I figured out how to find it for SAIDDES from your link...thanks again! I guess I'll need to use the same approach in order to know how the different section (e.i. IDDESdelta, IDDESDeltaCoeffs, smoothCoeffs, etc.) work all together. And about the 
    smoothCoeffs
    subdictionary, does someone has reference to suggest about the topic? Thank again for the help!
  • g
    has anyone used kw sst on rhoCentralFoam?
  • t
    Im wondering if someone know, in LES, how y+ is calculated? Do we use nu, nuEff or nuSgs? Since its unsteady, is it preferable to get a mean value or y+min and y+max over every recorded time step? Thanks for the help.
  • s
    $$ y^+ = \frac{u_\tau y}{\nu} $$
  • t
    slopezcastano

    https://cdn.discordapp.com/attachments/598785402391887872/1124310272119685170/725986814787059794.png▾

  • s
    $$ u_\tau = \sqrt{\frac{\tau_w}{\rho}} $$
  • t
    slopezcastano

    https://cdn.discordapp.com/attachments/598785402391887872/1124311018584146030/725986814787059794.png▾

  • t
    That's the function object code. So, nu, nuEff or nuSgs? y+mean or y+max for instance over all time step?

    https://cdn.discordapp.com/attachments/598785402391887872/1124315938251091988/image.png▾

  • s
    I understand LES as wall-resolved LES, so that function object is not correct for wall-resolved LES
  • s
    WMLES is another story
  • t
    Thank for answering and for your help. I'm trying to implement the Schaumann BC (related to atmospheric boundary layer simulation) and some authors say that the BC perform better when y+>20-30, so I'm trying to find out how it must be calculated..
  • s
    they use the formula above, but for u_tau they calculate the following:
  • s
    $$ u_\tau = \sqrt{\nu_t \frac{\partial U}{\partial y}} $$
  • t
    slopezcastano

    https://cdn.discordapp.com/attachments/598785402391887872/1124321601345830972/725986814787059794.png▾

  • s
    IT should be nu, not nu_t, if LES
  • s
    So, if you want to guarantee such in LES you must set your nuSgs to be zero at the wall boundary
  • t
    Ah.....I have to take a look....I maybe set this to zeroGradient....
  • t
    But again, regarding y+, the Shaumann BC involve applying a shear stress at the wall and it is function of the roughness lenght (z0), which mean its basically using this no? $$ u_\tau = \sqrt{\frac{\tau_w}{\rho}} $$
  • t
    t\_bo99

    https://cdn.discordapp.com/attachments/598785402391887872/1124322869921456170/574993721712443415.png▾

  • s
    Careful, here you are talking about WMLES
  • s
    $$ u_\tau = \sqrt{\frac{\tau_w}{\rho}} = \sqrt{\nu \frac{\partial U}{\partial y}} $$
  • t
    slopezcastano

    https://cdn.discordapp.com/attachments/598785402391887872/1124323598497235036/725986814787059794.png▾

  • t
    So, if I understand well, then using this should be approriate?
  • t
    This is what it look like:
  • t
    Copy code
    scalar uStar = (kappa * U) / Foam::log(z1 / z0);

//     Info << "planarAverage" << endl;
        Rw[facei].xx() = 0.0;
        Rw[facei].xy() = 0.0;
        Rw[facei].xz() = -sqr(uStar[facei]) * (UParallel[facei].x() / max(UParallelMeanMag, 1.0E-5));
        Rw[facei].yy() = 0.0;
        Rw[facei].yz() = -sqr(uStar[facei]) * (UParallel[facei].y() / max(UParallelMeanMag, 1.0E-5));
        Rw[facei].zz() = 0.0;
  • q
    What is an appropriate window when calcualting UPrime2Mean for the purpose of characterizing LES sims?
  • u
    Hello! I am trying to implement the kOmegaSST turbulence model into my compressible simulations of flow around a wedge. My solver is rhoCentralFoam. I believe I have set up my initial conditions correctly (0/ k omega nut alphat p U T), however, I keep receiving a floating point error when running rhoCentralFoam, relating to the nutkWallFunction. Is there more I had to do besides adding the necessary 0/ files?
  • u
    looking for general guidance!
  • u
    > I have set up my initial conditions correctly
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