  We perform three-dimensional gas-dynamical simulations and show that the
asymmetric morphology of the blue and red-shifted components of the outflow at
hundreds of astronomical units (AU) from the massive binary system eta Carinae
can be accounted for from the collision of the free primary stellar wind with
the slowly expanding dense equatorial gas. Owing to the very complicated
structure of the century-old equatorial ejecta, that is not fully spatially
resolved by observations, we limit ourselves to modelling the equatorial dense
gas by one or two dense spherical clouds. Because of that we reproduce the
general qualitative properties of the velocity maps, but not the fine details.
The fine details of the velocity maps can be matched by simply structuring the
dense ejecta in an appropriate way. The blue and red-shifted components are
formed in the post-shock flow of the primary wind, on the two sides of the
equatorial plane, respectively. The fast wind from the secondary star plays no
role in our model, as for most of the orbital period in our model the primary
star is closer to us. The dense clouds are observed to be closer to us than the
binary system is, and so in our model the primary star faces the dense
equatorial ejecta for the majority of the orbital period.
