Weak shock waves generated in 'Impulsive Sound Tube'

An impulsive sound wave or a weak blast wave below 100 Pa is generated by a spark discharge in a fully-developed turbulent air flow in a tube with a mean flow velocity of 1.6-34 m/s. The device was designated as an 'Impulsive Sound Tube (IST)'. The overpressure of a generated wave is observed by using two high-frequency microphones mounted flush with the tube wall. The observed profiles of overpressure differ strikingly depending on the flow velocity. It is concluded that the weak shock waves generated in IST can be partly- and fully-dispersed waves due to turbulence. The effective diffusivity of sound for turbulent flows is obtained as 1.6 x 10 to the -2nd sq m/s by fitting a Lighthill N-wave solution on the experimental data for rise times of the waves. It is also shown that a 'modified' Lighthill N-wave solution can give a consistent explanation to rise times of N-waves propagating across and along turbulent jet flows, and of sonic booms, as well as the rise times of the waves generated in IST.