Development of Time Measuring Technique to Measure the Shock Speed during the Propagation in the Free Atmosphere

Abstract

In the study of wave propagation in the free atmosphere, it is desirable to obtain time measurements to an accuracy of microsecond level. An experiment has been conducted to measure the wave speed during the propagation in the free atmosphere by the present technique. Due to sudden rupture of the diaphragm for the chamber pressure of 4.2 kg/cm2 and a wave generating in a shock tube travels with subsonic speed and the measured incident wave Mach number is 0.8 which leaves the shock tube in the free atmosphere. The measured travelling time of the incident wave to travel 61.5 cm distance in the shock tube is 2200 μsec and the same technique can apply to measure the shock wave speed. Several trigger points are installed at the exit of the shock tube in the open atmosphere to measure the strength of the wave propagation. It is observed that the wave strength decreases during the wave propagation in free atmosphere. Due to spherical expansion behind the wave, the pressure across the wave decreases. A numerical simulation is also conducted on supersonic shock wave to determine the shock speed and the travelling time in the free atmosphere. The pressures across shock wave at different locations of the shock wave are determined by solving the Euler equations and the simulation results indicate that the shock speed decreases during the propagation in the free atmosphere. In both experimental and numerical results, it is observed that the strength of the wave propagation in the free atmosphere decreases continuously due to spherical expansion.  The present technique can also be used to measure the supersonic jet velocity, the velocity of bullet and any particle velocity in subsonic or supersonic ranges.