Shearing Interferometer Study of Shock Wave Impact on Membranes

Abstract

A study was conducted to investigate the flow eld characteristics that form for a shock wave propagating through a membrane. Analysis was also done to determine the strength of the shock wave reflected back into the system as well as the strength of the shock wave that was transmitted through the membrane. Multiple tests were done to analyse the e ects of di erent material types as well as di erent back pressures. Six di erent materials were used, each with three di erent back pressures. The flow field visualisation was done using both schlieren fow visualisation and shearing interferometry flow visualisation using a Sanderson prism. A comparison between the two forms of visualisation was done to determine which would provide the best qualitative understanding of the flow field. From this it was found that the shearing interferometry flow visualisation gave better insight into the density gradients as well as provided a clearer view of the flow characteristics. When analysing the flow eld characteristics for the early development of the transmitted shock wave, there were three principal characteristics that were present in all of the tests; a di racted shock wave, an expansion wave and a recompression shock wave. It was found that the prominence of these features varied depending on the material type as well as the type of back pressure. For the later ow development and membrane rupture, there were ve principal characteristics; small vortices, secondary shock waves, a vortex ring, expansion waves and a Mach disk. When analysing the strength of the re ected and transmitted shock waves, it was found that their strengths did not vary signi cantly for the di erent back pressures. The only exception was found when conducting tests using a balloon as a membrane. This was because the balloon de ected further into and out of the shock tube. The balloon tests were therefore done for a wider range of vacuum back pressures. It was found that the more the balloon de ected the stronger the transmitted shock wave produced, while the re ected shock wave remained approximately the same. A relationship between the strength of the re ected and transmitted shock wave was formed. It was found that as the strength of the re ected shock wave increased the strength of the transmitted shock wave decreased.