NAVWEPS 00-8OT-80  HIGH SPEED AERODYNAMICS  TABLE 3-P. Suprnonk Wave Charactwiltks  Type  of wave formation  Flow direction change.  Efkct cm velociry and Mach  number.  Effect on static pressure and  density.  _-  Oblique shock wave  “Flow  into  a corner,”  turned into  preceding  flow.  Decreased  but still supcr-  sonic.  Increase.  :.  DKICaSe  _-  __  __  __  -  Normal shock wave.  No change.  Great increase,  Great decrease  __  -.  -.  -.  -  Expansion wwc.  ‘ / //  <  -  ,/$y  “Flow  around a corner,”  turned away from pre-  ceding flow.  Increased to higher super-  sonic.  DeCrWSe.  No change (no shock).  SECTIONS  IN  SUPERSONIC  FLOW  Parts (c) and (d) of figure 3.8 show the  wave pattern and resulting pressure distribu-  tion for a double wedge airfoil at zero lift.  The airstream moving over the surface passes  through an oblique shock, an expansion wave,  and another oblique shock. The resulting  pressure distribution on the surfaces  produces  no net lift, but the increased pressure on the  forward half of the chord along with the de-  creased pressure on the aft half of the chord  produces a “wave”  drag. This wave drag is  caused by the components of pressure forces  which are parallel to the free scream  direction.  The wave drag is in addition to the drag due  to friction, separatien, lift, etc., and can be  a very considerable part of the total drag at  high supersonic  speeds.  In order to appreciate the effect of these  various wave forms on the aerodynamic char-  acteristics  in supersonic  flow, inspect figure 3.8.  Parts (a) and (b) show the wave pattern and  resulting pressure distribution for a thin flat  plate at a positive angle of attack. The air-  stream moving over the upper surface passes  through an expansion wave at the leading edge  and then an oblique shock wave at the trailing  edge. Thus, a uniform suction pressure exists  over the upper surface. The airstream moving  underneath the flat plate passes through an  oblique shock wave at the leading edge then an  expansion wave at the trailing edge. This pro-  duces a uniform positive pressure  on the under-  side of the section. This distribution of pres-  sure on the surface  will produce a net lift and  incur a subsequent  drag due co lift from the in-  clination of the resultant lift from a perpen-  dicular co the free stream.  Parts (e) and (f) of figure 3.8 illustrate the  wave pattern and resulting pressure distribu-  tion for the double wedge airfoil at a small  positive angle of attack. The net pressure  213 