text: The principal differences between subsonic 
  
  The previous comparison points out three 1 
  significant differences between supersonic corn- 1 
  pressible and subsonic incompressible flow. 
  
  and supersonic flow are due to the cmprrs- 
  Jibi& 
  the supersonic flow. 
  Thus, any 
  change of velocity or pressure of a supersonic 
  flow will produce a related change of density 
  which must be considered and accounted for. 
  Figure 3.2 provides a comparison of incom- 
  pressible and compressible flow 
  through a 
  closed tube. Of course, the condition of con- 
  tinuity must exist in the flow 
  the 
  closed tube; the mass flow at any station along 
  the tube is constant. This qualification must 
  
  of 
  
  (a) Compressible flow includes the addi- 
  
  tional variable of flow density. 
  
  (b) Convergence of flow causes expansion 
  of incompressible flow but compression of 
  compressible flow. 
  
  (c) Divergence of flow causes compression 
  incompressible flow but expansion of 
  through 
  
  of 
  compressible flow. 
  
  204 
  
  Revised January 1965 