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Nozzle exit flow simulation

Question asked by Stagiair Avs on Dec 11, 2020
Latest reply on Dec 14, 2020 by Sylvain Grondin

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Hey all,

I am a mechanical engineer student and I'm on internship. For my internship I make flow simulations trough complex high pressure valves. Some valves need too cool and use nozzles.

Here is my problem. When I do a flow simulation in a nozzle is works well. But when I try to simulate what happends when it exits the nozzle, it just goes in a straight line. I've tried a number of things but can't seem to get it to work.

I was wondering if someone knows what I'm doing wrong, or if this is even possible.

I can't seem to attach the zip with my flow simulation in it. So here is the link: nozzle_assembly_flowsim.zip - Google Drive

Thanks in advance!

Greetings Cornee Smit

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Düse_Animation.mp44.6 MB

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Sylvain Grondin Dec 11, 2020 8:18 AM
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Hello,

I've seen your video but in your sldasm, cannot see any flow simulation project..

So, I don't really understand what would be wrong with your simulation, just with your video.

What do you expect to happen at the outlet ?
Or you want to see what happen after the exit ?
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- Stagiair Avs @ Sylvain Grondin on Dec 14, 2020 2:29 AM
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  Thanks for your response,
  
  The google drive link has the flow simulaiton project in it. But the file is to large.
  
  I expect the flow to diverge and spin after the nozzle exit. like a tornado comming out of it. We know from practice it does that.
  
  All I get when is simulate is a straight beam.
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Ronald van Til Dec 14, 2020 2:37 AM
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When I look at the mp4 it seems that the exit of the nozzle is also the end of the simulation. If you are interested in how the flow would exit the nozzle you need to model an additional volume after the nozzle. Than you could simulate the behavior of the flow exiting the nozzle and entering the (presumably larger) volume. I guess?
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- Stagiair Avs @ Ronald van Til on Dec 14, 2020 2:46 AM
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  you are right.
  
  I have tryed it, but as you can see. It goes out in a straight beam.
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  - Ronald van Til @ Stagiair Avs on Dec 14, 2020 9:37 AM
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    That looks really weird.... Is that en enclosed volume in which the nozzle exits? Volume should off course be substantially bigger in diameter than the nozzle itself. Is the volume filled with the same medium as that exits the nozzle? Should be, or else you need to define all kinds off stuff about how the media interact......
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    - Sylvain Grondin @ Ronald van Til on Dec 14, 2020 10:17 AM
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      I think it depends on type of boundary conditions he put on the other side of the volume.
      I would have put... atmospheric boundary conditions for the 5 faces of the volume he defined.. It should behave the same as external analysis IMO.
      Can't test it on my own (too slow download rate).
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Sylvain Grondin Dec 14, 2020 2:52 AM
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So, it's what Ronald van Til said : if you want to know what happend after the exit, you have to simulate the outside too ; so you have two choices :
- You can as he said, create a volume after the nozzle, but large enough to let the flow goes in without perturbation
- Or you can make an external analysis (which is better IMO), so you have to define your domain after the exit (you have to remove the lid) to let the flow develop after.

From the video, I guess it'll have the right behaviour after the exit.
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- Stagiair Avs @ Sylvain Grondin on Dec 14, 2020 4:53 AM
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  Did what you suggested and I am getting results!
  Thanks for that.
  
  The next problem accoured (see atteded pictures)
  It is not all the way round. It looks pretty weird.
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  - Ronald van Til @ Stagiair Avs on Dec 14, 2020 5:09 AM
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    I'm guessing internal flow would be better. The exiting flow from the nozzle needs to interact with material that is present in the volume it is exiting in. But it was a while ago I did some flow studies, so I'm not your best reference I guess.
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Sylvain Grondin Dec 14, 2020 5:22 AM
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Try just to increase the number of points
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- Stagiair Avs @ Sylvain Grondin on Dec 14, 2020 10:34 AM
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  That doesn't fix it. It makes the same pattren only more crowded
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  - Sylvain Grondin @ Stagiair Avs on Dec 14, 2020 11:43 AM
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    Okay, weird it doesn't match the external analysis case....
    Good it's working with the external one.
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Sylvain Grondin Dec 14, 2020 5:28 AM
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And yes, if you know what's after the exit (the volume in which the flow goes after the exit), you can model it with internal flow to better know what happen.
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Stagiair Avs Dec 14, 2020 5:30 AM
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Thank you both!
I am in the right direction because of you.

My question is answerd!
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Nozzle exit flow simulation

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