Results indicate that the second order Reynolds-stress model predicts characteristics common to this type of confined swirling flow, i.e. a Rankine vortex structure and a long, narrow reverse flow core. Lack of availability of experimental measurements of the flow field in mini-hydrocyclones forces a comparison with similarly proportioned 76-mm hydrocyclone velocity field characteristics. In these comparisons, the forced vortex portion of the 10-mm hydrocyclone is much more pronounced than in the 76-mm hydrocyclone in accordance with a smaller cross-sectional area for swirl development. A deficit in the axial velocity profiles of 76-mm hydrocyclones observed in the literature is reproduced in the 10-mm simulations. Also, the speculation concerning high levels of centrifugal acceleration inside the mini-hydrocyclone is demonstrated, with accelerations as high as 10,000 times gravity being present. Finally, separation efficiencies generated by the simulations are compared to experimental hydrocyclone separation efficiencies to check consistency with the flow field predictions.