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Help with aerodynamic shape considerations

  1. Apr 15, 2008 #1
    I have a flow acting perpendicular to a shape ie an airfoil however i dont think an airofoil is the best shape for the flow not to recirculate too much was wondering if anyone has any ideas? please view my attachment for basic drawing of the problem

    thank you


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  2. jcsd
  3. Apr 16, 2008 #2
    Whenever there is a flow obstruction perpendicular you will probably see separation/recirculation. May I ask what is the application, Reynolds number etc you are looking for? Your problem statement is rather vague.
  4. Apr 16, 2008 #3


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    I didn't want to be the first respondent here, since I don't really know anything about it, but I agree that the question is a bit vague. Are you looking to minimize the aerodynamic effects upon a necessary structure? Or are you trying to introduce a structure to alter airflow in some particular way?
  5. Apr 16, 2008 #4
    I am trying to minimize turbulence so i would like the Reynold number to be lower than the turbulent value of reynold number.
  6. Apr 16, 2008 #5


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    Okay, two more questions, then. Is the airflow always going to be impinging upon this structure from the same direction? What about variations in speed?
    My first thought is that some variation of a 'teardrop' cross-section would be best, but I'm no expert.
  7. Apr 16, 2008 #6
    yes the shape is always going to be impinging the airflow the velocity of air varies from 100 meters per second up to 300 meters per second
  8. Apr 16, 2008 #7


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    Wow... that's a lot faster than I expected. There might be some trans-sonic flow problems that change things at the higher end of that range. Fred or Russ are probably the best guys to handle this.
  9. Apr 16, 2008 #8
    At that speed I doubt your Reynolds number will be less then turbulent! Also is this in a duct, or open channel flow. In the first case the Reynolds number should be less then about 1200 for laminar flow.
  10. Apr 16, 2008 #9
    First off, those are very high velocities. High enough that you cannot consider the flow incompressible. So that makes this more complicated already.

    Second, if the impingement has to be perpendicular to the flow then what exactly are you trying to change?

    My only suggestion would be to streamline the side opposite of the incoming flow. This will reduce drag and likely reduce (to some degree) some of the turbulence.

    What are you looking to do with this device?
    What is the height (into the flow) of the bump relative to its length (parallel to the flow)?
  11. Apr 16, 2008 #10
    the device is use to introduce some form of liquid into the flow i haven't any specific specifications for the design just thinking about the shape trying to bea s aerodynamically sensible as possible.
  12. Apr 16, 2008 #11


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    Staff: Mentor

    That's exactly what I was thinking. Just build a fairing.

    But also, yes, we really need more info about what the intent is.
  13. Apr 16, 2008 #12


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    Sounds as if it's some sort of marker injector for a wind tunnel, but that doesn't make a lot of sense since that technology is old-hat.
    It isn't an art project, is it? Like that guy who throws paint behind a jet engine and lets it splatter on a canvas?
    Either way, I'm thinking that your aerodynamic profile has to be such that your fluid stream can be properly integrated into the airflow to achieve whatever purpose you have in mind. Whatever that purpose is, it can definitely impact upon what the most practical design will be.
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