7 Replies Latest reply on Jun 20, 2014 5:35 PM by Jared Conway

Unresolved Region - Fluid Subdomain

Travis Storm Jun 19, 2014 3:03 PM

I'm getting an "Unresolved Region" warning for "Condition name : Fluid Subdomain 1". What does that mean?

The model is just a propeller in a rotating region in freestream flow. I had this propeller in a simulation of an airplane and I wasn't getting this error. Now that I've removed the airframe, the error has started popping up.

Re: Unresolved Region - Fluid Subdomain

Jared Conway Jun 19, 2014 6:30 PM (in response to Travis Storm)

sounds like a geometry issue, i'd check this out:

http://www.hawkridgesys.com/blog/flow-simulation-4-starting-flow-simulation-analysis/

or your mesh is way too coarse

would really need more info about why you're using a fluid subdomain in this case
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- Re: Unresolved Region - Fluid Subdomain
  
  Travis Storm Jun 19, 2014 6:35 PM (in response to Jared Conway)
  
  Thanks Jared. I'm 99.99% (exactly) sure that it's not a geometry issue. It may be a coarse mesh issue, with cells spanning too much of the rotating region. I forced several refinements and it still didn't resolve the issue. I'll try a finer initial mesh and see if that helps.
  
  I'm using a fluid subdomain because that's how I was trained to insert farfield flow conditions. I don't see another way aside from building a cube around the fluid domain, doing an 'internal' flow, and applying velocity boundary conditions on the edges (that's how I would do it in other tools).
  
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  - Re: Unresolved Region - Fluid Subdomain
    
    Jared Conway Jun 19, 2014 6:55 PM (in response to Travis Storm)
    
    in flow simulation, just use an external analysis
    
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    - Re: Unresolved Region - Fluid Subdomain
      
      Travis Storm Jun 19, 2014 6:57 PM (in response to Jared Conway)
      
      This is probably an ignorant question, but since I was trained to use a subdomain, I'm confused. If you use an external analysis without a subdomain, where are freestream conditions set (i.e. how do you set the boundary conditions?)
      
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      - Re: Unresolved Region - Fluid Subdomain
        
        Jared Conway Jun 19, 2014 7:38 PM (in response to Travis Storm)
        
        initial/ambient conditions
        
        you're certainly welcome to do an internal analysis like a wind tunnel
        
        but even then, you don't need a fluid subdomain, your default fluid would apply
        
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        Re: Unresolved Region - Fluid Subdomain
        
        Travis Storm Jun 20, 2014 10:49 AM (in response to Jared Conway)
        
        Huh, ok. That's not at all intuitive to me... initial conditions are not the same as boundary conditions, by definition.
        
        But, in application, is there a difference between applying a fluid subdomain with my boundary conditions (velocity components, temperature, pressure) and applying initial/ambient conditions? I'm hoping they behave the same so my results to date aren't suspect.
        
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        Re: Unresolved Region - Fluid Subdomain
        
        Jared Conway Jun 20, 2014 5:35 PM (in response to Travis Storm)
        
        not sure if you have checked out the tutorials/validation examples but there should be an external flow analysis example that goes through this process if you want toget tuned into the way that flow works
        
        the method of building a wind tunnel is similar other than there are walls instead of freestream
        
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