Converging diverging nozzle

  1. i just started reading about nozzles and turbines in my semester course. i went through converging diverging nozzles. for achieving a supersonic flow, a converging diverging nozzle is used. now a converging section will work as a nozzle only till the flow is subsonic and a diffuser at supersonic flow. that means the maximum velocity obtainable in converging section is speed of sound in the same medium.
    also dA/A = [M^2 - 1]dV/V, at Mach 1, section ll not alter the speed of flow.
    now consider a converging diverging section. suppose mach 1 is reached at the throat, at mach 1, section ll not alter the speed of flow, then why would the flow become supersonic in the diverging section. i am a little confused about this. since no part of stream can go over mach 1 in converging section, diverging section should act as a diffuser, right?? apparently i am wrong, but i dont know where..
    also i was wondering what effect the shape of section might have, i mean concavity or convexity of the nozzle
     
  2. jcsd
  3. FredGarvin

    FredGarvin 5,087
    Science Advisor

    A properly designed CD nozzle will have it's throat at M=1. Compressible theory is where the divergent part starts to work. There are a few funny things that happen because of it. The acceleration of a flow in a divergent section is one of them. Keep reading!

    http://exploration.grc.nasa.gov/education/rocket/nozzle.html
     
    Last edited: Sep 6, 2007
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