Evaluating RANS turbulence models to predic the airflow in a duct bend

The main objective of this study is to evaluate the accuracy of some Reynolds Averaged Navier-Stokes (RANS) models to predict the behavior of the turbulent flows in a horizontal circular duct bend. The selection of the RANS models tested follows the capability of each model to describe the flow near the wall. Therefore, five turbulence models were selected: three Eddy Viscosity Models (two linear, k-ω SST and LRN (Low Reynolds Number) k-ε of Launder and Sharma, and one non-linear, cubic k-ε of Lien) and two Reynolds Stress Models (Launder Reece Rodi (LRR) and Speziale Sarkar Gatzki (SSG)). The numerical solutions were carried out using Computational Fluid Dynamics (CFD) code OpenFOAM® applied in an incompressible turbulent viscous flow. The grid discretization of the viscous sublayer leads to a refinement near to the walls and a smooth grid expansion ratio from the wall to the core of the pipe. The air flows with a Reynolds number of 6×104 through a straight circular duct of 0.104 m diameter followed by a 90° bend with curvature ratio of 4. The principal results were compared in terms of streamwise mean velocity profile and turbulence intensity contours. The turbulence models that performed better according to the velocity fields and turbulence intensity was the SSG. Nevertheless, none of them were able to accurately predict the flow next to the inner wall at the bend outlet.