The separation efficiency and the flow field of a dynamic cyclone were studied experimentally and simulated using commercial CFD software (FLUENT 6.0). The experimental results show that the rotational classifier position and the ratio of the classifier opening area to the inlet area have significant impact on the separation efficiency of the dynamic cyclone. The separation efficiency can be significantly improved as the classifier rotates at a speed beyond its natural swirling frequency. The RSM model was used to Simulate the 3-D gas flow field. and the simulation predictions were validated by the experimental results measured by a five-hole pressure probe. The tangential velocity distribution in the dynamic cyclone body can be divided into three zones: inlet, separation, and bottom. Each zone has its own tangential velocity distribution curve. The effects of operating conditions and geometric parameters of the classifier on the tangential velocity distribution were also studied. (c) 2005 Elsevier B.V. All rights reserved.