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Shock diamonds visible in a rocket or afterburning jet exhaust are caused by

  • A.Combustion occurring in discrete pulses
  • B.Vortex shedding from the nozzle lip
  • C.Condensation of water vapour in the plume
  • D.Waves reflecting between the plume boundary and axis

Answer: D

Waves generated at the lip cross the plume, reflect from the axis, travel to the constant-pressure boundary, reflect there with their sense reversed, and repeat. The alternating compression and expansion produces periodic bright regions where the gas is hottest, and the pattern decays as viscosity smears it out.

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