The main objective of the present study is to investigate the performance of different turbulent models for the flow simulation around a circular cylinder at a critical Reynolds number regime (Re = 8.5×105, Tu = 0.7%). To simulate the various flow features such as laminar-turbulent transition inside the boundary layer and the unsteady vortex shedding in the wake region, a hybrid RANS/LES model (SAS model) and a correlation-based transition model (γ - Reθ model) were used and the feasibilities of them for the flow simulation at a critical Reynolds number regime were demonstrated. A vertex-centered finite-volume method was adopted to discretize the incompressible Navier-Stokes equations and an unstructured mesh technique was used to discretize the computational domain. The inviscid fluxes were evaluated by using 2nd-order Roe’s FDS and the viscous fluxes were computed based on central differencing. A dual-time stepping method and the Gauss-Seidel iteration were used for unsteady time integration. To reduce the computational costs, the parallelization strategy using METIS and MPI libraries was adopted. The unsteady characteristics and time-averaged quantities of the flow fields were compared between the turbulent models. The numerical results have been also compared with experimental data. At the critical regime, turbulent models have showed quite different results due to the different abilities of each model to predict various flow features such as laminar-turbulent transition, unsteady vortex shedding.

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