  The rate at which small inertial particles collide with a
moderate-Reynolds-number spherical body is found to be strongly affected when
the formers are also settling under the effect of gravity. The sedimentation of
small particles indeed changes the critical Stokes number above which
collisions occur. This is explained by the presence of a shielding effect
caused by the unstable manifolds of a stagnation-saddle point of an effective
velocity field perceived by the small particles. It is also found that there
exists a secondary critical Stokes number above which no collisions occur. This
is due to the fact that large-Stokes number particles settle faster, making it
more difficult for the larger one to catch them up. Still, in this regime, the
flow disturbances create a complicated particle distribution in the wake of the
collector, sometimes allowing for collisions from the back. This can lead to
collision efficiencies higher than unity at large values of the Froude number.
