From the point of view of the influence of turbulence structure, this paper presents an elementary numerical analysis of the interaction between a particle and a gas phase. The effects of turbulence structure and the thickness of boundary layer on the separation efficiency in a cyclone separator have been investigated. The effects of the Saffman force on the particle trajectory are also analyzed. The results indicate that the separation efficiency decreases with an increase in turbulence intensity and increases with a decrease in the thickness of the boundary layer. The Saffman force can enhance the separation of small particles and also can shorten their residence time in the cyclone. (C) 2003 Elsevier Science B.V. All rights reserved.