Numerical simulation of turbulent flow in a Ranque-Hilsch vortex tube

The present work is about numerical simulations of the internal flow in a commercial model of a Ranque– Hilsch vortex tube (RHVT) operating in jet impingement. Simulation of the turbulent, compressible, high swirling flow was performed by both RANS and LES techniques. The effect of different turbulence closure models have been tested in RANS simulations using a first order closure RNG k–e and, for the first time in this kind of flow, a second order RSM (Reynolds Stress differential Model) closure. RANS computations have been executed on an axis-symmetric two-dimensional mesh and results have been compared with LES ones, obtained over a three-dimensional computational grid. Smagorinsky sub-grid scale model was used in LES. All the calculations were performed using FLUENTTM 6.3.26. The use of a common code for the different simulations allowed the comparison of the performances of the different techniques and turbu- lence models, avoiding the introduction of other variables. In all the simulations performed, consistency with the real commercial vortex tube model in jet impingement operation has been followed by substituting an axial hot computational exit to the usual radial one. Comparison of the results between RANS simulations performed on both a traditional radial hot outlet computational domain and one with an axial hot outlet, demonstrates the suitability of the computational model adopted in this work, closer to the real geometry of the device, particularly in RANS RSM simulations. Results in different sections of the tube show significant differences in the velocity pro- files, temperature profiles and secondary vortex structures, varying turbulence model. The accurate numerical simulation of the flow in a RHVT, resulting in an improved prediction capability of the kinematic and thermal properties of outgoing jets, could allow a correct estimation of the cooling performance of this device in jet impingement operation.