  We propose that the large, radius of ~1000 AU, circumbinary rotating disks
observed around some post-asymptotic giant branch (post-AGB) binary stars are
formed from slow AGB wind material that is pushed back to the center of the
nebula by wide jets. We perform 2D-axisymmetrical numerical simulations of fast
and wide jets that interact with the previously ejected slow AGB wind. In each
system there are two oppositely launched jets, but we use the symmetry of the
problem and simulate only one jet. A large circularization-flow (vortex) is
formed to the side of the jet which together with the thermal pressure of the
shocked jet material accelerate cold slow-wind gas back to the center from
distances of ~1000-10000 AU. We find for the parameters we use that up to 0.001
Mo is back-flowing to the center. We conjecture that the orbital angular
momentum of the disk material results from the non-axisymmetric structure of
jets launched by an orbiting companion. This conjecture will have to be tested
with 3D numerical codes.
