  We present the first self-consistent, three dimensional study of hydrodynamic
simulations of mass transfer in binary systems with bipolytropic (composite
polytropic) components. In certain systems, such as contact binaries or during
the common envelope phase, the core-envelope structure of the stars plays an
important role in binary interactions. In this paper, we compare mass transfer
simulations of bipolytropic binary systems in order to test the suitability of
our numerical tools for investigating the dynamical behaviour of such systems.
The initial, equilibrium binary models possess a core-envelope structure and
are obtained using the bipolytropic self-consistent field technique. We conduct
mass transfer simulations using two independent, fully three-dimensional,
Eulerian codes - Flow-ER and Octo-tiger. These hydrodynamic codes are compared
across binary systems undergoing unstable as well as stable mass transfer, and
the former at two resolutions. The initial conditions for each simulation and
for each code are chosen to match closely so that the simulations can be used
as benchmarks. Although there are some key differences, the detailed comparison
of the simulations suggests that there is remarkable agreement between the
results obtained using the two codes. This study puts our numerical tools on a
secure footing, and enables us to reliably simulate specific mass transfer
scenarios of binary systems involving components with a core-envelope
structure.
