Numerical simulations of the flow around tandem circular cylinders in the subcritical and postcritical regimes

Abstract

As idealized as it may seem, the structures with tandem circular cylindrical profiles are widely found in engineering applications. As the action of the wind does not spare any buildings, the aerodynamic study of these structures is necessary. Therefore, the challenging unsteady flow around smooth and rough tandem cylinders in the subcritical and postcritical regimes is studied through numerical simulations with a rigorous methodology. This thesis aims to assess the ability of 2D URANS simulations to capture the mean and fluctuating quantities and the flow behavior. Experimental data are introduced as principal reference results. The use of wall function boundary conditions is also assessed in both flow regimes, and only very small center-to-center spacings between cylinders are considered. Two turbulence models are employed in the URANS simulations: the k-omega SST model and the Langtry-Menter 4-equation Transitional SST model. On the one hand, from preliminary studies, the former model is more suitable for the postcritical regime with wall function boundary conditions. On the other hand, the second model with a resolved viscous layer is more adapted for the subcritical regime as the boundary layer on the upstream cylinder is laminar before separation. For the smooth case, URANS simulations yield very accurate estimations of main quantities in the subcritical regime. In the postcritical regime, the mean flow quantities are captured, and the global wake is narrower as the upstream separation is delayed, which allows using wall functions. The simulations predict the expected shear layer reattachment on the downstream cylinder for both regimes. Regarding roughness, it is only modeled by wall functions. For both regimes, the flow around rough cylinders is simulated thanks to the k-omega SST model. High discrepancies appear with experimental data for the subcritical regime as wall functions are not adapted for such separated flow. In the postcritical regime, wall functions yield satisfactory results compared to experiments, especially for the upstream cylinder. Notwithstanding the necessary improvements for simulating the flow around rough tandem cylinders in the subcritical regime, the present methodology can be used for further applications on the flow around tandem cylinders.