A numerical model has been developed (HAAS), that predicts the velocity field in axis-symmetric flows with high swirl- and Reynolds numbers in cyclone geometries, together with trajectories of particles released in this field. Since HAAS is a kinematic model based on integrals of the flow field, it is much faster than CFD. Using HAAS, a prototype de-oiling hydrocyclone separator, the DelftCyclone, was developed. In this paper HAAS is explained, and its predicted results are compared with those obtained from detailed simulations using a commercial CFD code: Fluent (V6.0.12), and with results from laboratory experiments. The pressure drop and flow field from HAAS compare quantitatively well with those from Fluent; however, compared to laboratory experiments, both models overestimate the pressure drop by some 80%. The predicted separation efficiencies are trendwise correct, but both overestimate, partly because turbulent dispersion was ignored. It is concluded that the HAAS model is very time-efficient in the design of axial hydrocyclones, and because of its speed it can be used as an interactive tool with real-time output. On the other hand, more realistic flow simulations are valuable for geometry refinement, because they can resolve details that are not included in the coarse HAAS model. (C) 2004 Elsevier Ltd. All rights reserved.