PARTIALLY-AVERAGED NAVIER-STOKES SIMULATION OF TURBULENT FLOW IN A SQUARE DUCT

In this study, a modified formulation of the partially-averaged Navier-Stokes (PANS) model is suggested for accurate prediction of the turbulent secondary flow in a square duct. The model performance is assessed by a detailed comparison of PANS predictions to the LES and RANS results and available DNS results. The LES, original PANS (oPANS), and seven-equation RANS models resolved the secondary flow which is distributed near the corners of the square duct. The secondary flow demonstrated four pairs of counter-rotating vortices with a symmetrical distribution. Compared with the seven-equation RANS model, the high-velocity region was widely distributed near the corners predicted by the LES and oPANS model. They resolve the high strength of the secondary flow, which transfers more energy from the center to the corners. Therefore, the LES and oPANS model predicted the strong secondary vortices better than the RSM. On the other hand, in the two-equation RANS model, a different form of secondary flow was identified. The mean secondary velocity vectors rotated around the center of the duct. Thus, the two-equation RANS model failed to capture a similar secondary flow to those predicted by the LES and oPANS model.The grid resolution used in the simulations was too dense to use for the RANS simulation in the industry due to an excessive increase in computational cost. The comparatively coarse grid suitable for the RANS simulation was generated and used for the original PANS simulation. On the other hand, the original PANS simulation failed to capture the secondary flow near the corners of the square duct. The modified PANS models required a model constant, and the model constant was determined that could resolve the secondary flow in the square duct.