  Aims: In order to understand the first stages of planet formation, when tiny
grains aggregate to form planetesimals, one needs to simultaneously model grain
growth, vertical settling and radial migration of dust in protoplanetary disks.
In this study, we implement an analytical prescription for grain growth into a
3D two-phase hydrodynamics code to understand its effects on the dust
distribution in disks. Methods: Following the analytic derivation of Stepinski
& Valageas (1997), which assumes that grains stick perfectly upon collision, we
implement a convenient and fast method of following grain growth in our 3D,
two-phase (gas+dust) SPH code. We then follow the evolution of the size and
spatial distribution of a dust population in a classical T Tauri star disk.
Results: We find that the grains go through various stages of growth due to the
complex interplay between gas drag, dust dynamics, and growth. Grains initially
grow rapidly as they settle to the mid-plane, then experience a fast radial
migration with little growth through the bulk of the disk, and finally pile-up
in the inner disk where they grow more efficiently. This results in a bimodal
distribution of grain sizes. Using this simple prescription of grain growth, we
find that grains reach decimetric sizes in 10^5 years in the inner disk and
survive the fast migration phase.
