The present study analyzes the clustering, collision and agglomeration of solid particles in laminar and turbulent fluid flows. By applying direct numerical simulations, the effect of various boundary conditions such as particle inertia and solid volume fraction on the clustering and collision of spherical point particles in homogeneous isotropic turbulence is investigated on the mesoscale particle level. In addition, the fluid dynamical interaction between approaching particles shortly before their collision as well as the flow induced agglomeration of primary particles is evaluated using a second microscale approach in which the particle surface is resolved by the numerical grid. In this context, the obtained agglomerate structures are characterized by various morphological parameters. The used computing program is based on the lattice-Boltzmann method.