  Large Eddy Simulation (LES) with dynamic sub-grid scale eddy viscosity model
has been applied to numerically investigate the evolution of complicated flow
structures in supersonic base flow with mass bleed. Mean flow properties
obtained from numerical simulations, such as axial velocity, pressure on the
base surface, have been compared with the experimental measurements to show
that LES is able to predict the mean flow properties with acceptable accuracy.
The data obtained from LES has been further analyzed to understand the
evolution of coherent structures in the flow field. Periodical shedding of
vortical structures from the outer shear layer has been observed and it has
also been found that this vortex shedding is associated with the flapping of
the outer shear layer. The frequency of flapping of the outer shear layer has
been found out and the phase-averaged streamlines have been analyzed to further
study the evolution of vortical structures associated with this flapping. The
phase-averaged streamline plots clearly elucidate the evolution of vortical
structures along the outer shear layer. Further, the study of these structures
is investigated by performing Proper Orthogonal Decomposition (POD) analysis of
the data, obtained along the central plane in the wake region. The POD results
also seem to agree well with the observations made in the phase averaged
streamline plots, as the concentrated energy and enstropy are observed in the
outer shear layer with fewer POD modes.
