SimScale CAE Forum

Unexpected high velocity and red frame around model

Hello,

I’m currently trying to simulate the flow around an impeller inlet. There are two things, that really concern me:

  1. the velocity gets up to >2000 m/s while the initial velocity is about 15 m/s. I really don’t know where these high speeds come from and I have tried other simulations with a similar profile and it does not always happen. I just can’t figure out why it does sometimes!

  2. around the profile as well as the flow channel appears a red frame which I don’t know if it means that there is a velocity oder if it’s just a frame? I hope it does not mean that there is a high speed as the speed should be zero at the wall
    https://www.simscale.com/projects/aefthymiou/abwasserpumpe_optimum/

I appreciate any help. Thanks a lot!
Kind regards
Anna

Hi Anna, thank you for using the forum!

So you want to simulate only part of an impeller’s blade. right? Not the whole blade?

Best regards,
Fillia

Hey Filia,

yes that’s correct. It is supposed to be only the entrance of the impeller. We cut it out of a CAD model so we can analyze what happens only at the inlet.

kind regards
Anna

Hi Anna, the issue here is mesh related. There are some bad cells in the mesh that produce high values, and you can locate these by using the Isovolumes method that is described here:
How to Check and Improve Mesh Quality | SimScale Documentation (check section 2.2)

Also, make sure to set the top, sides, and bottom faces to Slip walls instead on No-slip. It would also be helpful to use the Extend face feature of the CAD mode so you can increase the domain size across all directions.

Best regards,
Fillia