The phenomenon of preferential concentration of inertial particles is studied by following lagrangian trajectories. Elementary properties of the coarse-grained distribution of heavy particles in simple turbulent flows are investigated by direct numerical simulations. In the small Stokes number case, we compute the coarse-grained particle distribution, ${\overline n}_r$, and we demonstrate that the second moment $ \langle {\overline n}_r^2 \rangle$ behaves as an approximate power law : $ \langle {\overline n}_r^2 \rangle \sim r^{\alpha} $. The dependence of the exponent $\alpha$ as a function of the Reynolds and of the Stokes number is studied in the small Stokes number limit. Our results show a strong dependence of the level of fluctuation of the particle distribution as a function of the Reynolds number.