Why is my Flightstream ground-plane unsteady simulation not converging?

BuggsBunny
BuggsBunny Altair Community Member
in Community Q&A

Hello,

I'm trying to model a vehicle in hover and cannot get the solution to converge. If you could shed some light on why the solution is not converging, it would help a lot.

What I have tried:

  1. Tried a single propeller without ground (viscous and inviscid) and it works.
  2. Tried two propellers and without ground, and it still works (both viscous and inviscid)
  3. As soon as I add the ground, it does not converge.
  4. I have tried varying the mesh size.
  5. I have tried converging the inviscid first and then the viscous.
  6. I have tried adding the ground to the excluded boundaries list.
  7. I have tried limiting the wake to 1 revolution.
  8. Played with the stabilization strength.
  9. Modelled ground in different ways.

None of the solutions seem to work. I have attached the simulation file for more info.

Question 2) I have added two propellers because I do not understand why there is a difference in pressure contours between the two propellers as they are essentially the same propellers spinning in different directions.

Thanks

Ground_not_converging.zip
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Answers

  • denriquez
    denriquez
    Altair Employee

    Great job troubleshooting!

    After review, I believe the issue is that your mesh surface normals are inverted. A common scenario. If you click the green cube in the top tool bar you can view the normals. One of the propellers is all red, meaning the mesh normals are pointing inward. Simply select the component and flip the normals using the highlighted button. Let me know if this helps

    image.png
  • BuggsBunny
    BuggsBunny Altair Community Member

    Ahh! That solved my second question. Now I'm getting similar forces from both my propellers without a ground plane.

    But the solution is still not converging when I add a ground plane. Could you please help me figure out why the solution is not converging?

    Thank you.

  • denriquez
    denriquez
    Altair Employee

    Can you share a screenshot of what you are seeing? I would also suggest setting the AoA to 0deg since your velocity is near 0 anyways. After flipping the surface normals, the solution seems to work fine for me.

  • BuggsBunny
    BuggsBunny Altair Community Member
    ground_not_converging.mp4

    This is what is happening.

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