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Id: 810028

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  • Id: 810028

    Considering subsonic incompressible airflow through a Venturi, which statement is correct? 1. The static pressure in the undisturbed airflow is higher than in the throat. 2. The speed in the undisturbed airflow is higher than in the throat.

    According to the answer 1) is incorrect and 2) is correct.
    However,I always thought (and answered in similar questions) that the speed in the throat is higher. So this would mean 2 is incorrect.
    Besides, the static pressure decreases in the throat, right? So this would mean that it is indeed higher in the undisturbed airflow, which would mean 1 is correct.

    Can someone please explain if this is a faulty question or if I misunderstood anything?
    Last edited by Pinuts; 03-06-2020, 14:34.

  • #2
    Mass flow rate = area x density x velocity

    For steady state flow mass flow rate is constant
    For incompressible flow density is constant
    Therefore if area decreases velocity increases

    So 2) is incorrect

    Bernoulli's equation for incompressible flow states that

    Static pressure + 1/2 density x velocity squared = constant
    Therefore if velocity increases static pressure decreases

    So 1) is correct


    • #3
      With other words, you also agree with me that the questions is incorrect? :P


      • #4
        The way you wrote it - yes, I agree with you that the question is faulty.
        However, I just checked the disputable question (810028), and the correct answer is: 1) is correct and 2) is incorrect.
        It might have been corrected in the meantime.