Experimental investigation of weak irregular shock wave reflections
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Date
2010-03-25T06:10:53Z
Authors
Li, Gavin Sun Man
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Abstract
An experimental investigation of weak shock wave reflections was conducted with the large
scale shock tube in the Flow Research Unit, in the Mechanical Engineering Laboratory, at the
University of the Witwatersrand, Johannesburg. The purpose of the study was to expand the
current understanding of irregular shock wave reflections, especially the von Neumann
reflection (vNR) and the Guderley reflection (GR). The experiments were conducted using a
high sensitivity schlieren system for three Mach numbers in the region around M 1.10 with
single-frame and multiple-frame cameras. The single-frame photographs were taken to
visualise the sequences of expansion fans and shocklets behind the reflected shock wave,
while the multiple-frame photographs were taken using a million-frame per second camera
for the velocity calculation in the region near the triple point indicated in oblique shock wave
theory. Most of the single-frame photographs show the first set of expansion fans and
associated shocklet clearly, while a few of them show signs of the second set of expansion
fans and shocklet. The third expansion fan is not very clear on some photographs, and there is
no sign of the third shocklet at all. Most of the multiple-frame photographs were useful for the
oblique shock calculations. The work done is the first time to obtain quantitative data on flow
through a Guderley reflection. The lower burst pressure (1.8 bar) tests were proven to be most
successful for the study while the higher burst pressure (3 bar) tests showed contradictions to
the physical meaning of the flow behind the reflected shock wave. This is due to the
assumption of plane shock waves in the oblique shock calculations, recognizing that the
physical shock wave has a very large curvature and the substantial weakness of the reflected
wave, being close to sonic conditions. Some primary computational fluid dynamics (CFD)
simulations using an Euler code, were also conducted to inform the design of a new insert to
vary the angle of the divergent section of the shock tube to improve the visibility of the
expansion fans and shocklets behind the reflected shock wave. The new insert has not been
tested due to time constraint.