The effects of the cone dimensions on the flow field in a cyclone separator were investigated computationally. Three cyclones with different cone tip diameters were studied using the commercial CFD code FLUENT. The difficulty of modeling high swirling flow is overcome by means of Reynolds Stress Model (RSM) and Large Eddy Simulation (LES). The axial and tangential velocities in the cyclone are successfully simulated and analyzed with the aid of velocity components, static pressure and dynamic pressure contour plots for the flow field. Results obtained demonstrate that LES is a suitable approach for modeling the effects of cyclone dimensions on the flow field.