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Converging-Diverging Nozzle

  1. Mar 5, 2014 #1

    Maylis

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    1. The problem statement, all variables and given/known data
    2. Air flows from a large supply tank in which the pressure is 147 psig and the temperature is 160 F through a converging - diverging nozzle. The velocity at the throat of the nozzle is sonic. A normal shock occurs at a point in the diverging section of the nozzle where the cross-sectional area is 1.44 times the cross-sectional area of the throat.

    a) Compute the Mach number, pressure, and temperature just upstream of the shock.
    b) Compute the Mach number, pressure, and temperature just downstream of the shock.


    2. Relevant equations



    3. The attempt at a solution
    I thought the slide 9 would be the equation to use for this problem, but if S* is what they mean, that is just the cross sectional area of the throat, right? What is S supposed to be without the Asterisk?

    I am not sure how I could determine the mach numbers up and downstream of the shock using any of the equations give in the lecture slides. is Po, To, etc just at the ''back pressure'' (back pressure is the tank pressure, right?)
     
  2. jcsd
  3. Mar 5, 2014 #2

    SteamKing

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    We have no idea what 'slide 9' refers to.
     
  4. Mar 5, 2014 #3

    Maylis

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    My apologies, I intended to post the slides
     

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  5. Mar 9, 2014 #4

    Maylis

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    I am just using the equation on the 9th slide. Honestly, I can't really say I understand what the equation means. I know S* is the cross sectional area where the velocity is sonic (the throat), but my best guess is that S is an arbitrary cross section anywhere along the pipe. However, I wonder if it is only for the divergent part of the nozzle?

    slide 10 summarizes all the equations, and of course T, P, ρ, etc are probably corresponding with S? It explicitly states T0, P0, etc. are at the reservoir, but doesn't mention what T, P, etc are.

    I am uncertain of what it meant by ''just upstream of the shock'' or ''just downsteam'' and how I am supposed to calculate these. Just upstream can be anything upsteam, what are they asking for more precisely?

    This table seems to agree with my calculation of the mach number being 1.80
    http://www.cchem.berkeley.edu/cbe150a/isentropic_flow.pdf
     

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    Last edited: Mar 9, 2014
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