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# incompressible
  • f

    finn

    12/01/2025, 4:20 PM
    But I think that is still physically incorrect, but it might be (much) better, it is as if it is downstream as if you had infinite many of them stacked and you look at the last one
  • f

    finn

    12/01/2025, 4:27 PM
    3 hours 'a long time', damn life is good
  • k

    kandelabr

    12/01/2025, 6:20 PM
    I mean, a single blade/channel and all stages, like https://cdn.discordapp.com/attachments/726377664213942323/1445117325023121530/image.png?ex=692f2de3&is=692ddc63&hm=46f252b1aaff27bdebcff277c4c4925f2f19d9bb8468abb8ced982ed8e040850&
  • z

    Zhavok

    12/01/2025, 6:53 PM
    Keep discussing. I'll eagerly await the result 🤣. When two experts disagree, there is always something to learn 😅
  • f

    finn

    12/01/2025, 7:01 PM
    Ow I do not disagree
  • k

    kandelabr

    12/01/2025, 7:59 PM
    it's a common practice, not my idea 🙂
  • l

    lennygo

    12/02/2025, 9:34 AM
    This is the correct approach
  • l

    lennygo

    12/02/2025, 9:34 AM
    Industry standard approach
  • l

    lennygo

    12/02/2025, 9:35 AM
    or well "correct" I should state that its a simplification which gives accurate results while keeping simulation times reasonable
  • l

    lennygo

    12/02/2025, 9:35 AM
    thats always the preferred answer
  • f

    finn

    12/02/2025, 9:40 AM
    excactly
  • z

    Zhavok

    12/02/2025, 10:48 AM
    So, have I understood correctly? It is sufficient to analyze only one stage for the blade shape?
  • l

    lennygo

    12/02/2025, 10:48 AM
    yes, if you apply the correct boundary conditions
  • l

    lennygo

    12/02/2025, 10:49 AM
    no sorry, you should do one Blade through all the stages
  • l

    lennygo

    12/02/2025, 10:49 AM
    because for only one stage with 1 stator and 1 rotor for accurate results you would have to know not only the inlet, maybe atmospheric conditions, but also the following stages pressure distribution, which you probably dont have
  • z

    Zhavok

    12/02/2025, 10:52 AM
    Ah ok. Thank you 👍 👍 👍
  • z

    Zhavok

    12/02/2025, 10:53 AM
    Before I continue working on it today, I have one more question. The entire construction is very small. The outer diameter of the blades will be approximately 60 mm. How large should the distance be between: 1. Rotor blades and stator blades 2. Stator blades and rotor blades
  • z

    Zhavok

    12/02/2025, 10:53 AM
    (2. means to the next stage)
  • z

    Zhavok

    12/02/2025, 10:55 AM
    So I don't need a perfect formula, just a value that you would take based on your experience.
  • l

    lennygo

    12/02/2025, 11:07 AM
    Try half a chord or 1/3 a chord
  • z

    Zhavok

    12/02/2025, 11:28 AM
    Thank you very much for all your tips. I will construct a complete prototype and upload it here as a .step file soon 👍
  • l

    littleB123

    12/02/2025, 2:05 PM
    So for an incompressible study. I have a zone where there i some kind of separation. K-omega-SST dont converge on my GCI, so i found an article that uses to k-epsilon to model the same thing as i do ( a bend pipe). and wanted to see if i could get a better GCI study here. My nusselt number and friction_factor are highly unstable (see picture). I haven't used k-epsilon that much before. My y+=0.17. Are there anything obvious i have missed?? https://cdn.discordapp.com/attachments/726377664213942323/1445415606370173120/image.png?ex=693043af&is=692ef22f&hm=3f78ed3040af1552a127096f8843595a8af8126661e6a47b18609a4d702cf1d4&
  • k

    kandelabr

    12/02/2025, 2:08 PM
    AFAIK, k-epsilon isn't too happy with low-re meshes?
  • l

    littleB123

    12/02/2025, 2:09 PM
    Yes ive heard that as well. Wolfdynamic notes also mention this. I am just very confused that several studies are using ths approach with good results?
  • k

    kandelabr

    12/02/2025, 2:10 PM
    There's a low-re correction somewhere in the settings but I don't have experience with that. Never actually managed to run k-epsilon successfully
  • y

    Yann

    12/02/2025, 2:13 PM
    the ``lowReCorrection`` in the ``epsilonWallFunction``? https://gitlab.com/openfoam/core/openfoam/-/blob/master/src/TurbulenceModels/turbulenceModels/derivedFvPatchFields/wallFunctions/epsilonWallFunctions/epsilonWallFunction/epsilonWallFunctionFvPatchScalarField.H
  • l

    littleB123

    12/02/2025, 2:15 PM
    Just found this the very moment!
  • l

    littleB123

    12/02/2025, 2:15 PM
    There is also a kLowRe function?
  • k

    kandelabr

    12/02/2025, 2:16 PM
    and nut
  • l

    littleB123

    12/02/2025, 2:18 PM
    Yes. But i just realised. I adjsuted all my wall to have different wall functions for my k-omega-SSt case. I used cp -r 0.oirg to replace it in my relevant case (many by now) and ive just learned that it doesnt repalce the file within the directioy you copying if they already exist... So that could also explain my problem with convergence in GCI... - But thanks!