Interaction of a Mach 1.2 Shock with a Single Cylinder
This
page shows simulations from the interaction of a shock with a cylinder
of gas. The cylinder is composed of Sulphur Hexafluoride (SF6). The
rest of the shocktube is filled with air. A shock of Mach number 1.2
is introduced into the shock tube and allowed to impact the
cylinder. The experiment was carried out at Los Alamos National
Lab. Experimental setup is shown here (PDF
File) (although this is for two cylinders rather than one). The
initial conditions (volume concentration through a cross-section of
the cylinder) are shown here (GIF image)
. Simulations were carried out with the FLASH code, Version 2.3,
at the ASCI FLASH Center. The PPM method, without steeping, was
used. Refinement was done on the first rather than second derivatives
(which is the default for FLASH). The calculations included 2 fluids,
air and SF6.
Questions to be answered
Any study of this kind raises a few questions, and we list here a few
issues that come to mind and need to be addressed:
Do the simulations converge with increasing level of resolution?
Is this convergence reflected in both external appearance as well as
diagnostics such as velocity, concentration etc?
What is the influence of various numerical techniques such as the
hydrodynamic method, effect of discontinuity steepening etc?
The maximum concentration of SF6 is not known. How do different
concentrations affect the solution?
How well are the initial and boundary conditions characterized,
for example how clearly is the shock delineated?
In 2 dimensions we neglect vertical motions of the SF6 gas? Are
those important, and if so how do we get a handle on them?
Available Diagnostics and Observables
Overall morphology, gas density distribution, SF6 concentration,
velocity field - Are all these quantities available, and if so is it
meaningful to use them for comparison? How should such a comparison be
made?
How well is the experiment repeatable, i.e. can instabilities
such as the Kelvin-Helmholtz instability that are seen in some of the
results be reproduced easily? What are the typical mesurement errors?
What additional data is required to analyse the experiment? For
example, we need to know physical properties of SF6 such as viscosity.
What is the Reynolds number for the experimental setup, as well
as the simulations?
The results below show density snapshots of the evolution of the
cylinder cross-section. Clicking on the images or the "density" and
other links will bring up animated 'gif' movies.
Density 
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Density 
