  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.
