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Help required to understand dynamic pressures

  1. Aug 10, 2009 #1
    Hi all,

    I am trying to understand the concept of dynamic and static pressures and would appreciate your help.

    I've got a nozzle flow setup, such that the flow is exhausting into atmosphere. Am I right in assuming that the dynamic pressure at exit (relative to atmosphere) is equivalent to 1/2*rho*v2 and the gauge static pressure = 0?

    Thanks for your time in advance!
     
  2. jcsd
  3. Aug 10, 2009 #2

    tiny-tim

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    Welcome to PF!

    Hi aero_g! Welcome to PF! :smile:

    (have a rho: ρ :wink:)
    Yes, the gauge pressure = 0.

    But I think saying "dynamic pressure at exit (relative to atmosphere)" is wrong …

    I don't think there's any such thing as "gauge" dynamic pressure, so dynamic pressure is always defined as 1/2 ρv2, and Patm is irrelevant.

    (from the PF Library on pressure …)
     
  4. Aug 10, 2009 #3
    Re: Welcome to PF!

    Hi there!

    Thanks for your reply. You are right, "dynamic pressure at exit (relative to atmosphere)" is wrong …

    Following that, the total pressure at exit is then = dynamic pressure (since static pressure = 0). Am I right in saying that?
     
  5. Aug 10, 2009 #4

    tiny-tim

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    Yup! :smile:
     
  6. Aug 10, 2009 #5
    Thank you very much!!!!
     
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