This article reports on the latest experiments in the series of
Richtmyer–Meshkov instability (RMI) shock-tube experiments.
Previous work described a double-bump experiment that evidenced some
degree of unrepeatability. The present work features an enlarged
perturbation introduced to improve repeatability. In common with the
previous work, the experiments were conducted at shock Mach number 1.26
(70 kPa overpressure), using the Atomic Weapons Establishment 200
× 100 mm shock tube with a three-zone test cell arrangement of
air/sulphur hexafluoride/air. The sulphur hexafluoride gas
(SF6) was chosen for its high density (5.1 relative to air)
providing an Atwood number of 0.67. Gas separation was by means of
microfilm membranes, supported by fine wire meshes. A double-bump
perturbation of two-dimensional geometry was superimposed on the
downstream membrane representing a 0.6% addition to the dense gas
volume. Visualization of the turbulent gas mixing was by laser sheet
illumination of the seeded SF6 gas using a copper vapor
laser pulsing at 12.5 kHz. Mie scattered light was recorded using a
35-mm rotating drum camera to capture a sequence of 50 images per
experiment. Sample experimental results shown alongside corresponding
three-dimensional hydrocode calculations highlight the problems in both
analysis and comparison caused by multiple scattering arising from the
necessary use of a high seeding concentration. Included is a
demonstration of the effectiveness of introducing into the hydrocode a
Monte Carlo-based simulation of the multiple scattering process. The
results so derived yield greatly improved qualitative agreement with
the experimental images. Quantitative analysis took the form of
deriving relative intensity data from line-outs through experimental
images and their code equivalents. A comparison revealed substantial
agreement on major features.