  Many astrophysical flows occur in inhomogeneous media. The broad-line regions
(BLR) of active galactic nuclei (AGNs) are one of the important examples where
emission-line clouds interact with the outflow.
  We present results of a numerical study of the interaction of a steady,
planar shock / supersonic postshock flow with a system of embedded cylindrical
clouds in a two-dimensional geometry. Detailed analysis shows that the
interaction of embedded inhomogeneities with the shock / postshock wind depends
primarily on the thickness of the cloud layer and the arrangement of the clouds
in the layer, as opposed to the total cloud mass and the total number of
individual clouds. This allows us to define two classes of cloud distributions:
thin and thick layers. We define the critical cloud separation along the
direction of the flow and perpendicular to it. This definition allows us to
distinguish between the interacting and noninteracting regimes of cloud
evolution. Finally we discuss mass-loading in such systems.

Astrophysics