This paper presents a numerical study of flow over a circular cylinder at high Reynolds number using detached-eddy simulation (DES). The k-C Shear Stress Transport (SST) based DES model is selected for handling massively separated flow. The computations are performed with an Otype grid and the instantaneous and statistical characteristics of the turbulent wake flow behind the cylinder is extensively studied. The results are compared with the available experimental data, as well as the previously published numerical data obtained from Reynoldsaveraged Navier-Stokes (RANS) and large-eddy simulation (LES). The incompressible flow assumption and finite volume discretization is adopted. All the works are carried out with the use of OpenFOAM toolbox.

The Reynolds-Averaged Navier-Stokes (RANS) equations are widely used to model turbulence in industrial applications for its cheap costs. RANS do not mean to resolve any turbulent flow structures at any scale, but to model the time-averaged turbulent properties using varies kinds of mathematical formulations. All turbulent fluctuations are eliminated during the time averaging. Therefore, it is inaccurate to predict massively separated flows which contain detached eddies at different length scales. While the unsteady RANS (URANS) attempts to solve the problem but with little efforts. The large-eddy simulation (LES) and direct numerical simulation (DNS), on the other hand, is capable for accurately predicting unsteady flows since most turbulence eddies are resolved, but the cost is expensive mainly because the dense grid resolution at boundary layer and small time steps. Detached-eddy simulation (DES), as a hybrid RANS/LES method, combines the best part of the two worlds. The basic idea of DES is to model the attached flow near wall and to resolve the detached and free shear flows in the other regions. The original version of DES was proposed by Spalart et al. (1997). The version, referred as DES97 here, is a modification of the one-equation Spalart-Allmaras eddy viscosity model (Spalart and Allmaras, 1994). DES97 was soon discovered to be sensitive to wallparallel grids in the boundary layers. It is caused by the simple and crude split of RANS and LES region. The improper arrangement of wall-parallel grids spacing results in the wrong regions for RANS and LES. The region in outer part of boundary layers which should be modeled by RANS turns to be resolved by LES. While the grid refinement is not enough to resolve all the eddy viscosities. A new version called delayed DES (DDES) was proposed by Spalart et al. (2006) to address that issue. Based on the basic idea of the hybrid model, Menter el al. (2003) also proposed the SST based DES model by modifying the two-equation SST model (Menter, 1994). The SST version of DES provides a "shield" which can prevent grid induced separation (GIS) and address model stress depletion (MSD).