Newcastle University

Results of segregation (de-mixing) of inertial particles in turbulent flows are presented and analysed. Calculations were performed on a model of synthetic turbulence and in Direct Numerical Simulations of statistically stationary homogeneous isotropic turbulence, under the assumption that the system is dilute (i.e. forces acting on the flow caused by heavy particles are neglected). Trajectories of inertial particles introduced randomly into the fluid (with the same velocities as the local flow) were calculated based on Stokes drag. Results showed good agreement between the two numerical methods for more than one Stokes number (defined as the normalized particle relaxation number). In particular, it was found that particles segregate primarily in regions where the particle velocity field is compressed. The compressibility of the particle phase has been evaluated via a Lagrangian parameter, the deformation tensor J, which measures the deformation of an infinitesimal volume surrounding a particle and its evolution in time along each particle trajectory. In particular, results confirmed that values for which the volume contraction is equal to zero occur when the compressibility tends to a negative infinite value. This was attributed to the presence of singularities which correspond to a sudden collapse of the volume occupied by the particles. Spatially averaged statistics of the particle number density were also preliminary investigated