STABILITY OF SHOCK-BOUNDED SLABS
Brian S. Marks &
John M. Blondin
Finally, a preprint is
available in our Preprint Library.
(Submitted to New Astronomy , August 1, 1996)
Recent hydrodynamic simulations have suggested that a slab of cold, dense
gas, bounded on both sides by isothermal shocks, is dynamically unstable.
Ethan Vishniac (ApJ 428, 186) has named this the
"Nonlinear Thin Shell Instability" (NTSI), because the instability
requires a nonlinear perturbation to the planar slab.
We have studied such shock-bounded slabs using the numerical
hydrodynamics code VH-1.
Sinusoidal perturbations were added to planar slabs to
determine the characteristics of the dynamical evolution as a function
of the wavelength and amplitude of the perturbation relative to the
width of the slab. We confirm Vishniac's claim that perturbations with
amplitudes larger than the width of the slab are dynamically unstable:
the NTSI. Given a
suitable initial perturbation and a sufficiently large Mach number, the
perturbation will grow unbounded. However, in many cases our results
show that the breathing mode of the perturbed slab can "outrun" the
shredding motion of the NTSI, causing the perturbations to pinch off
and form a relatively flat, albeit thick, slab that remains confined in
space. We have also investigated perturbations due to
dense clouds
advected into an unperturbed planar slab. These perturbations often
lead to the NTSI effects as well.