*** WARNING: Diss.-rate fully specified by two-layer wall treatment

Jagan Adithya Elango
Jagan Adithya Elango Altair Community Member
edited July 2023 in Community Q&A

Hello experts, I am trying perform steady state conjugate heat transfer analysis of motor with k-epsilon turbulence model.

I have meshed air gap with two cells on the either side of MRF. I'm getting this warning (*** WARNING: Diss.-rate fully specified by two-layer wall treatment) in log file.

Is this something I should be concerned about? 

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Answers

  • acupro
    acupro
    Altair Employee
    edited July 2023

    That warning is likely related to the turbulence conditions specified at inflow boundaries.  Can you attach the .inp/.Log files?

    Unrleated - but if you only have four cells between walls (split by the MRF boundary) that's only three internal nodes, which doesn't give much ability to capture much of the flow gradient/profile.

    If you want to stick with a k-epsilon model, the realizable is likely the better choice.

  • Jagan Adithya Elango
    Jagan Adithya Elango Altair Community Member
    edited July 2023
    acupro_21778 said:

    That warning is likely related to the turbulence conditions specified at inflow boundaries.  Can you attach the .inp/.Log files?

    Unrleated - but if you only have four cells between walls (split by the MRF boundary) that's only three internal nodes, which doesn't give much ability to capture much of the flow gradient/profile.

    If you want to stick with a k-epsilon model, the realizable is likely the better choice.

    Thanks for your reply.

    You are right, I have used 4 cells to model 1mm airgap after referring CFD analysis of 75KW PMSM motor with SimLab ( Tutorials, How To, Troubleshooting - Multi-physics (EM, NVH, CFD) Analysis of a 75 kW PMSM with SimLab (altair.com) )

    image

    I will proceed with realizable K epsilon in future.

  • acupro
    acupro
    Altair Employee
    edited July 2023
    Jagan_21383 said:

    Thanks for your reply.

    You are right, I have used 4 cells to model 1mm airgap after referring CFD analysis of 75KW PMSM motor with SimLab ( Tutorials, How To, Troubleshooting - Multi-physics (EM, NVH, CFD) Analysis of a 75 kW PMSM with SimLab (altair.com) )

    image

    I will proceed with realizable K epsilon in future.

    That warning is likely benign, as it goes away after the first time step.

    Convergence (based on residual/solution ratio) is not great.  You may want to add more mesh and/or decrease the Solution Update Factor (yields a larger relaxation factor in the input file) to see if that helps.

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