  We investigate experimentally the spatial distributions of heavy and
neutrally buoyant particles of finite size in a fully turbulent flow. As their
Stokes number (i.e. ratio of the particle viscous relaxation time to a typical
flow time scale) is close to 1, one may expect both classes of particles to
aggregate in specific flow regions. This is not observed. Using a Voronoi
analysis we show that neutrally buoyant particles sample turbulence
homogeneously, whereas heavy particles do cluster. One implication for the
understanding and modeling of particle laden flows, is that the Stokes number
cannot be the sole key parameter as soon as the dynamics of finite-size objects
is considered.
