The fluid flow and oil-water separation were simulated using a Reynolds stress transport equationmodel of turbulence in water flow and a stochastic model of oil droplet motion. Simulation results give the axialand tangential velocity components, the pressure and turbulence intensity distribution and droplet trajectories fora hydrocyclone of F type and a hydrocyclone proposed by the present authors. The flow field predictions are inqualitative agreement with the LDV measurements. The results show that the proposed hydrocyclone has betterperformance than the hydrocyclone of F type due to creating stronger centrifugal force and lower axial velocity.