  The problem of accretion of small particles by a sphere embedded in a mean
flow is studied in the case where the particles undergo inelastic collisions
with the solid object. The collision efficiency, which gives the flux of
particles experiencing at least one bounce on the sphere, is found to depend
upon the sphere Reynolds number only through the value of the critical Stokes
number below which no collision occurs. In the absence of molecular diffusion,
it is demonstrated that multiple bounces do not provide enough energy
dissipation for the particles to stick to the surface within a finite time.
This excludes the possibility of any kind of inelastic collapse, so that
determining an accretion efficiency requires modelling more precisely
particle-surface microphysical interactions. A straightforward choice is to
assume that the particles stick when their kinetic energy at impact is below a
threshold. In this view, numerical simulations are performed in order to
describe the statistics of impact velocities at various values of the Reynolds
number. Successive bounces are shown to enhance accretion. These results are
put together in order to provide a general qualitative picture on how the
accretion efficiency depends upon the non dimensional parameters of the
problem.
