Shearing Interferometer Study of Shock Wave Impact on Membranes
Date
2019
Authors
Schulz, Jennifer
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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.
Description
dissertation submitted to the Faculty of Engineering and the Built Environment, University
of the Witwatersrand, Johannesburg, in ful lment of the requirements for the degree of Master of Science in Engineering.
Johannesburg, May 2019
Keywords
Citation
Schulz, Jennifer Marion. (2019). Shearing interferometer study of shock wave impact on membranes. University of the Witwatersrand, https://hdl.handle.net/10539/28789