  This fluid dynamics video shows visualizations of a Large-Eddy Simulation
(LES) of an over-expanded planar nozzle. This configuration represents the
experimental setup of Papamoschou et. al. which found the position of the
internal shock to be unstable. Our LES calculations confirm this instability
and offer a vibrant and dynamic view of the underlying flow physics. The
interaction between shock and turbulent boundary layer is shown as is the
subsequent separation region downstream. Numerical Schlieren provide a glimpse
of the low frequency shock motion and suggest potential mechanisms for the
instability. Key features include the asymmetry of the shock structure (with
large and small lambda shocks), compression and expansion waves downstream of
the shock and large scale flow reversal. Full details of the experiment and the
calculation can be found in the references.
