  The present paper proposes a two-phase flow model that is able to account for
two-scale kinematics and two-scale surface tension effects based on geometric
variables at small scale. At large scale, the flow and the full geometry of the
interface may be retrieved thanks to the bulk variables, while at small scale
the interface is accurately described by volume fraction, interfacial area
density and mean curvature, called the geometric variables. Our work mainly
relies on the Least Action Principle. The resulting system is an extension of a
previous work modeling small scale pulsation in which surface tension was not
taken into account at large or small scale. Whereas the original derivation
assumes a cloud of monodispersed spherical bubbles, the present context allows
for polydispersed, non-spherical bubbles. The resulting system of equations
solely involves small scale geometric variables, thus contributing in the
construction of a unified model describing both large and small scales.
