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Two-dimensional expansion wave diffraction around a 90⁰ convex corner.

The di raction of a one-dimensional expansion wave over a 90 corner was explored using
experiment and simulation methods. Unlike studies in shock di raction, expansion wave
di raction was hardly explored in the literature and therefore is considered as novel. Two
independent parameters were identi ed for the present study: 1) the initial diaphragm
shock tube pressure ratio, and 2) the position of the diaphragm from the apex of the 90
corner. The experimentation only considered variation in the shock tube pressure ratio
whereas the simulation varied both independent parameters. A Navier-Stokes solver with
Menters SST k-! turbulence model was found to adequately model the
ow eld.
A number of major
ow features were identi ed, that occurred in the vicinity of the 90
corner. The
ow features identi ed were: a shear layer which originated by
ow separation
near the apex of the 90 corner, a separation bubble that remained attached to a wall
boundary in absence of rig-dependent e ects, and a re
ected compression wave due to
perturbation signals generated by di raction of the expansion wave.
For a narrow-width expansion wave existing prior to di raction, it was found that after
di raction a re
ected compression wave developed which would steepen into an outwardly
propagating, weak, cylindrical shock wave. Other major
ow features identi ed were a
strong indication of an oblique shock located near the separation bubble and a large wake
region immediately downstream of the separation bubble. The wake region, through
schlieren imaging, was found to consist of two distinct layers.
The experimental results through shadowgraph and schlieren imaging have indicated
large-scale turbulent structures within the separation bubble and the shear layer. Shear
layer instability and vortex shedding o the separation bubble were also evident. The
Navier-Stokes solver was found not to resolve the experimentally observed turbulence, the wake region and the vortex shedding.

Identiferoai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/13736
Date12 February 2014
CreatorsMahomed, Irshaad
Source SetsSouth African National ETD Portal
LanguageEnglish
Detected LanguageEnglish
TypeThesis
Formatapplication/pdf, application/pdf

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