A computational fluid dynamic model is used to predict the flow fields and the associated temperature separation within a Ranque-Hilsch vortex tube. The large eddy simulation (LES) technique was employed for predicting the flow and temperature fields in the vortex tube. A vortex tube with a circumferential inlet stream and an axial (cold) outlet stream and a circumferential (hot) outlet stream was considered. The temporal evolutions of the axial, radial and azimuthal components of the velocity along with the temperature, pressure and density fields within the vortex tube are simulated. Performance curves (temperature separation versus cold outlet mass fraction) were obtained for a specific vortex tube with a given inlet mass flow rate. Simulations were carried out for varying amounts of cold outlet mass flow rates. Predictions from the present large eddy simulations compare favorably with available experimental measurements. (c) 2007 Elsevier Ltd. All rights reserved.