The aerodynamic dispersion of bulk powders is important for a number of applications including particle characterisation, and the delivery of therapeutic drugs via the lung using dry powder inhalers (DPIs). Complete aerodynamic dispersion of cohesive clusters is very challenging to achieve, due to large interparticle attractive forces compared to dispersive forces. In this paper the distinct element method (DEM) coupled with continuum models for the fluid phase flow to simulate fluidsolids interactions is used to investigate the aerodynamic dispersion of different sized cohesive clusters in a uniform fluid flow field. The simulations have shown that aggregate dispersion behaviour is dependent on the relative aggregate size (i.e. the ratio of aggregate diameter to primary particle diameter). If the aggregate size is small, it appears as though the aggregate disintegrates; however, for larger aggregates, the dispersion process switches to a gradual peeling of the particles from the surface layers. These two dispersion processes have been analysed through investigating dispersion rate and it has been shown that the dispersion rate decreases as the aggregate size increases. Furthermore, different regions within the aggregates have been studied and confirm that for larger aggregates the surface particles disperse more rapidly than internal particles; however, for smaller aggregates, dispersion is essentially occurring everywhere in the aggregate. (C) 2012 Elsevier Ltd. All rights reserved.