  We have performed interface-resolved direct numerical simulations of forced
homogeneous-isotropic turbulence in a dilute suspension of spherical particles
in the Reynolds number range Re-lambda=115-140. The solid-fluid density ratio
was set to 1.5, gravity was set to zero, and two particle diameters were
investigated corresponding to approximately 5 and 11 Kolmogorov lengths. Note
that these particle sizes are clearly outside the range of validity of the
point-particle approximation, as has been shown by Homann & Bec (2010). At the
present parameter points the global effect of the particles upon the fluid flow
is weak. We observe that the dispersed phase exhibits clustering with moderate
intensity. The tendency to cluster, which was quantified in terms of the
standard deviation of Voronoi cell volumes, decreases with the particle
diameter. We have analyzed the relation between particle locations and the
location of intense vortical flow structures. The results do not reveal any
significant statistical correlation. Contrarily, we have detected a small but
statistically significant preferential location of particles with respect to
the `sticky points' proposed by Goto & Vassilicos (2008), i.e. points where the
fluid acceleration field is acting such as to increase the local particle
concentration in one-way coupled point-particle models under Stokes drag. The
presently found statistical correlation between the `sticky points' and the
particle locations further increases when focusing on regions with high local
concentration. Our results suggest that small finite-size particles can be
brought together along the expansive directions of the fluid acceleration
field, as previously observed only for the simplest model for sub-Kolmogorov
particles. We further discuss the effect of density ratio and collective
particle motion upon the basic Eulerian and Lagrangian statistics.
