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Subsonic diffuser is an expanding pipe

  1. Mar 28, 2005 #1

    books says
    Subsonic diffuser is an expanding pipe.

    In a picture it shows A -> B the radius of pipie decreases.

    I was under the impression that subsonic and expanding pipe meant radius getting larger.

    please clarify .. thanks again
  2. jcsd
  3. Mar 28, 2005 #2
    also is there a definition for shock.... or formula? my book doesn't give a definition
  4. Mar 30, 2005 #3


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    Gold Member

    Maybe your book is upside down :rofl: . A subsonic diffuser is a pipe whose radius becames larger as we advance in axial direction (flow direction).

    As far as shocks are concerned, a Shock Wave is a flow discontinuity in compressible flow. Variables such as velocity, pressure and temperature have a "virtual" discontinuity across the Shock Wave.

    And I have mentioned the word "virtual" because such discontinuity doesn't happen in real flow. In fact Navier-Stokes formulae don't admit any discontinuity, because viscous diffusion always make a smoothing effect over the flow. Only the unreal theory of inviscid flow deals with discontinuities. Traditionally such discontinuities have been called "Shock Waves", and they have a mathematical structure based on the Rankine-Hugoniot jump conditions.
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