  We carry out 2D viscous hydrodynamical simulations of circumbinary accretion
using the AREPO code. We self-consistently compute the accretion flow over a
wide range of spatial scales, from the circumbinary disk (CBD) far from the
central binary, through accretion streamers, to the disks around individual
binary components, resolving the flow down to 2% of the binary separation. We
focus on equal-mass binaries with arbitrary eccentricities. We evolve the flow
over long (viscous) timescales until a quasi-steady is reached, in which the
mass supply rate at large distances $\dot{M}_0$ (assumed constant) equals the
time-averaged mass transfer rate across the disk and the total mass accretion
rate onto the binary components. This quasi-steady state allows us to compute
the secular angular momentum transfer rate onto the binary,
$\langle\dot{J}_b\rangle$, and the resulting orbital evolution. Through direct
computation of the gravitational and accretion torques on the binary, we find
that $\langle\dot{J}_b\rangle$ is consistently positive (i.e., the binary gains
angular momentum), with $l_0\equiv\langle\dot{J}_b\rangle/\dot M_0$ in the
range of $(0.4-0.8)a_b^2\Omega_b$, depending on the binary eccentricity (where
$a_b,~\Omega_b$ are the binary semi-major axis and angular frequency); we also
find that this $\langle\dot{J}_b\rangle$ is equal to the net angular momentum
current across the CBD, indicating that global angular momentum balance is
achieved in our simulations. We compute the time-averaged rate of change of the
binary orbital energy for eccentric binaries, and thus obtain the secular rates
$\langle\dot a_b\rangle$ and $\langle \dot{e}_b\rangle$. In all cases,
$\langle\dot{a}_b\rangle$ is positive, i.e., the binary expands while
accreting. We discuss the implications of our results for the merger of
supermassive binary black holes and for the formation of close stellar
binaries.

High Energy Astrophysical Phenomena;Earth and Planetary Astrophysics