Development and validation of a CFD model prediction of temperature separation in swirling fluid flows

In this study, a numerical model was developed for performing 3D computational fluid dynamics (CFD) simulations of the total temperature separation phenomenon in rotating flows, and the accuracy of this model was validated. This study aims to confirm that the CFD simulation results accurately reflect the physical processes occurring in a real swirling fluid flow. This study examines a rotating fluid flow in a counterflow Ranque-Hilsch vortex tube. The commercial three-dimensional CFD solver Ansys CFX 2024 R2 is used for calculations in a steady-state formulation. To determine the required mesh resolution, a grid convergence study was conducted using the Grid Convergence Index (GCI). The obtained indicators meet the GCI requirements in detailed studies with low error margins (GCI ≤ 5%). The selected mesh for further calculations comprises 13 million elements. This study includes simulations of the vortex tube at various cold stream mass fractions and with different turbulence models. Specifically, the standard k-ε model, the Shear Stress Transport (SST) model, and two Reynolds Stress Models were considered: the Baseline Reynolds Stress Model (BSL RSM) and the Speziale-Sarkar-Gatski Reynolds Stress Model (SSG RSM). The results of the 3D CFD simulations were compared with experimental data, particularly analyzing the difference in total temperatures between the hot and cold outlets of the vortex tube at varying static pressures at the hot outlet. Based on the analysis, all considered turbulence models are capable of detecting the total temperature separation in rotating flows. However, the standard k−ε turbulence model demonstrated the best agreement with the experimental data in terms of the degree of temperature separation. Therefore, it is recommended for use in energy separation calculations in rotating flows.