10 Replies Latest reply on Nov 22, 2010 1:47 PM by Bill McEachern

Particle study in cyclone separator

1-CSA37M Mar 9, 2010 10:46 AM

I'm analyzing a cylcone separator with air and solid particles.

I have problems with calculating and displaying the particle trajectories. It says in the result summary box that their 'fate' is "maximum time step". However, the 'residence time' for all 20 particles is between 1 and 2 seconds. I have specified the maximum time to 3600 seconds on the settings tab when i set up the particle study.

In help it says:

"Maximum time. Stops the particle's trajectory when the particle traveling time has reached the specified maximum value."

Why does it stop before it satisfies this criterium? Have I overlooked or misunderstood something?

Se attached for pictures of cyclone and dialog boxes.

Thanks!

Cyclone separator.jpg 102.4 KB
Particle study settings.jpg 174.6 KB

Re: Particle study in cyclone separator

Richard Stevenson Mar 24, 2010 10:32 AM (in response to 1-CSA37M)

what is the reflection setting for your study?
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- Re: Particle study in cyclone separator
  
  1-CSA37M Mar 24, 2010 10:42 AM (in response to Richard Stevenson)
  
  Ideal reflection.
  
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Re: Particle study in cyclone separator

David Paulson Mar 24, 2010 12:09 PM (in response to 1-CSA37M)

If you hide your flow trajectories then you will able to see the particles better. You can also increase the number of particles displayed.
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- Re: Particle study in cyclone separator
  
  1-CSA37M Mar 24, 2010 12:28 PM (in response to David Paulson)
  
  There are no particle trajectories in the image I've posted. The image is to show the geometry of the cyclone to make things clear. And, increasing the number of particles does not solve the issue I'm experiencing. Thanks for the input anyways.
  
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  - Re: Particle study in cyclone separator
    
    David Paulson Mar 24, 2010 2:07 PM (in response to 1-CSA37M)
    
    Your results summary indicates that you do have particles but they are not being displayed. So, your settings are fine, and almost identical to the settings I used in a similar study which I have attached as a jpeg. When you RMB click Injection does it display "show" or "hide"?
    
    Oil Separator Particle Study.JPG 76.9 KB
    
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    - Re: Particle study in cyclone separator
      
      1-CSA37M Mar 24, 2010 2:19 PM (in response to David Paulson)
      
      Sorry about the confusion, but the image and the dialog boxes are not connected. The image is purely to show the geometry. The reason I also display the flow paths is that I want to hide some geometric features that my client wants to be confidential.
      
      I have no trouble displaying the particle trajectories. The issue is that the trajectories terminate by some reason I cannot understand.
      
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      - Re: Particle study in cyclone separator
        
        David Paulson Mar 25, 2010 1:12 AM (in response to 1-CSA37M)
        
        I now understand that your particle trajectories are visible, but they end prematurely. I tried to replicate the "Maximum time step" you are getting in your results summary by changing the particle size in my study, but my particles only were absorbed because that is my wall condition, not reflection. But you might see if your results change if you make your particles smaller or larger. For my designs I have to run a number of different particle sizes to reflect the real input stream. Or you could just change your wall condition to "absorb" and see if you get the same "Maximum time step" message in the results summary.
        
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Re: Particle study in cyclone separator

1-CSA37M Mar 25, 2010 3:33 AM (in response to 1-CSA37M)

I asked my VAR about this issue, and they asked the development team which after a while replied the following:

"The 'maximum time step' is limited by the 'maximum iteration count' at 100 000. There is SPR 477646 to increase the user-defined 'maximum iteration count' to values greater than 100 000. The developers were not currently able to say in what version this setting will be increased. Unfortunately there is no workaround."

I.e. I know why this happens, but I can't really do anything about it.

Also, particles may 'get stuck' in vortices etc which is relevant for this case.
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- Re: Particle study in cyclone separator
  
  David Harrold Nov 22, 2010 1:39 PM (in response to 1-CSA37M)
  
  Hi Maria,
  That's an interesting problem.
  Would decreasing the mesh quality help? I'd assume that a coarser mesh would yield a lower iteration count. I know that's not the right way to solve the problem, but it would be interesting to know if it had an effect.
  
  I am modeling a similar cyclone separator and did not run into the issue you had. The "max time steps" works as expected. I'm running SW 2011, SP0.0, so maybe the issue has been fixed. Here's a picture:
  
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  - Re: Particle study in cyclone separator
    
    Bill McEachern Nov 22, 2010 1:47 PM (in response to David Harrold)
    
    I ran into the same problem in one I just did a couple days ago in 2011 sp0. It went off to the developers as well.
    
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