  The dynamics and stability of a thin gas layer moving between two fluid
layers moving in the same or opposite direction is studied. The linear
evolutionary equations describing the spatial-temporal dynamics of the
interface perturbations between gas and two fluid layers are derived for the
flat two-dimensional case. Integral correlations across the layer are obtained,
and the various kinds of time dependent base states are found. A linear
stability is considered for the system using non-stationary equation array
derived. The equation array consists of the two one-dimensional non-stationary
equations of a seventh and fourth order. The results of the numerical study of
the governing evolution equations support the results of the analysis for more
simple limit cases. It is found that the thin sheet gas flow in-between two
liquid layers is unstable and the peculiarities are found and discussed
together with some applications available.
