Unstable Solution in Forced Convection

Jagan Adithya Elango
Jagan Adithya Elango Altair Community Member
edited October 2022 in Community Q&A

I'm solving air-forced convection of motor using k epsilon turbulence model. I'm getting these warnings:

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

WARNING: inflow at outflow boundary: Outlet (mass/time: in=-2.920399e-03, out=4.139305e-02)

And my solution tends to be unstable.

image

I have attached pictures and input file for reference, Please give me an insight about this warnings and suggest if changes need to be made in the modelling. Thank you.

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Answers

  • acupro
    acupro
    Altair Employee
    edited September 2022

    In many instances when there is a large expansion between the inlet and outlet, you'll get reverse flow (backflow) at the outlet.  This is likely what's happening here.  There are typically two options:

    1. Activate backflow conditions on the outflow boundary - and define the turbulence and temperature conditions of any incoming flow.  Maybe 'average exiting' as the type?

    2. Add a contraction beyond your area of interest - maybe beyond your current outflow to get back to maybe a similar exiting area to the inlet area - similar to the image below where the exit is at the top of the image.  You can make the boundaries 'slip' on the outside of that extension/contraction so as not to influence pressure drop too much if that is of interest.
    image

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