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Need advice on how realistic these CFD results are. Intuitively they seem way off.

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  1. Apr 1, 2012 #1
    I am using Solidworks to model the pressure distribution of air around a large fan. The fan is 10' in diameter and moves 94,000 CFM. I need to know the effect adding a large duct around the inlet of the fan would have on the pressure. If the duct causes a huge pressure drop then we can't use it.

    The duct would completely enclose the inlet and extend 18'. After modeling the air flow Solidworks tells me the lowest-pressure point in the entire duct would be only 0.4 psi below atmospheric pressure. It seems to me that a fan of this size pulling air through 18' of duct would cause much lower pressure than that.

    I have added some pictures of the model and results. Air enters through the rectangular inlet shown in the two pictures of the model. It exists through the opening, which I have modeled as a red disk. As you can see the pressure inside the duct is barely below atmospheric pressure. Intuitively it seems like it should be much lower. As a new engineer with little experience my intuitive frame of reference may not be realistic. Any thoughts?

    The length units in the attached pictures are in inches.
     

    Attached Files:

  2. jcsd
  3. Apr 2, 2012 #2

    AlephZero

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    Re: Need advice on how realistic these CFD results are. Intuitively they seem way off

    Using Bernouilli's equation (assuming the air is incompressible) will give you a sanity check on what pressure changes to expect.
     
  4. Apr 2, 2012 #3
    Re: Need advice on how realistic these CFD results are. Intuitively they seem way off

    We did that and found a much higher pressure difference than that predicted by Solidworks. I'll just have to go back to the model and see if I made any mistakes.
     
  5. Apr 3, 2012 #4
    Re: Need advice on how realistic these CFD results are. Intuitively they seem way off

    Your first mistake was to use Solidworks.

    In my experience (admittedly a few years ago now) Solidworks is workable if you want to compare flow paths on, for example, different iterations of a model but if you're after an absolute value don't bother.
     
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