Claudio Mannini

Three-Dimensional Numerical Simulation of Flow Around a 1 : 5 Rectangular Cylinder

This paper deals with the three-dimensional simulation of the unsteady flow around a stationary 1:5 rectangular cylinder at zero-degree angle of attack, low Mach number and relatively high Reynolds number. The computations have been performed using the DLR-Tau code, a non-commercial finite-volume code developed at the German Aerospace Center, and results obtained with a hybrid mesh are validated against the available experimental data, showing good agreement. Detached-Eddy Simulation (DES), that is a hybrid method combining Large-Eddy Simulation (LES) and Raynolds-Averaged Navier-Stokes (RANS) approaches, has been adopted as strategy of turbulence modelling. The comparison with respect to unsteady RANS results, although obtained with advanced turbulence models, show the improvement that can be expected with the DES technique for this type of massively separated bluff-body flows. The paper also clarifies the key role played in LES, and therefore also in DES simulations, by the artificial dissipation characterizing the numerical scheme used to discretize the filtered Navier-Stokes equations. Finally, the discussed results highlight the effects of the spanwise extension of the computational domain. A distance between the periodic boundary planes equal to the width of the cylinder is not enough to allow the natural loss of correlation of pressures and the free development of large-scale turbulent structures. In contrast, a span equal to the double of the cylinder width fulfill much better this requirement.

URANS and DES Simulation of Flow Around a Rectangular Cylinder

This paper deals with numerical simulation of the flow around a 1:5 rectangular cylinder. The Unsteady Reynolds-Aver aged Navier-Stokes (URANS) and Detached-Eddy Simulation (DES) computational techniques are employed. In the process the influence of various modelling parameters, such as turbulence modelling, and flow parameters, such as Reynolds number and incidence angle, is investigated. Simulations with both stationary and harmonically oscillating body are performed. Validation of computed results with experimental data shows that the URANS-based computational approach is capable of predicting the basic unsteady flow phenomena in the considered cases. These results are further confirmed by the DES method, which provides information about the instantaneous flow variables and offers a deeper insight into the flow physics.

Applicability of URANS and DES Simulations of Flow Past Rectangular Cylinders and Bridge Sections

This paper discusses the results of computational fluid dynamics simulations carried out for rectangular cylinders with various side ratios of interest for many civil engineering structures. A bridge deck of common cross-section geometry was also considered. Unsteady Reynolds-averaged Navier–Stokes (URANS) equations were solved in conjunction with either an eddy viscosity or a linearized explicit algebraic Reynolds stress model. The analysis showed that for the case studies considered, the 2D URANS approach was able to give reasonable results if coupled with an advanced turbulence model and a suitable computational mesh. The simulations even reproduced, at least qualitatively, complex phenomena observed in the wind tunnel, such as Reynolds number effects for a sharp-edged geometry. The study focused both on stationary and harmonically oscillating bodies. For the latter, self-excited forces and flutter derivatives were calculated and compared to experimental data. In the particular case of a benchmark rectangular 5:1 cylinder, 3D detached eddy simulations were also carried out, highlighting the improvement in the accuracy of the results with respect to both 2D and 3D URANS calculations. All of the computations were performed with the Tau code, a non-commercial unstructured solver developed by the German Aerospace Center.