Comparison of modelled reynolds stresses for mild separation using RANS, DES and DDES schemes

The present study is focused to evaluate the accuracy of the Detached-Eddy Simulation (DES), Delayed Detached-Eddy Simulation (DDES) and Reynolds Averaged Navier-Stokes (RANS) equations for a mild separation case. An in-house code dynamic grid detached eddy simulation `DG-DES´ is used. The modeled turbulent Reynolds stresses are computed as a reference quantity. The flow around Aerospatiale A-airfoil at maximum lift with angle of attack α=13.3° and at a Reynolds number of 2× 10⁶ is taken as the test case. The detailed experimental data for this case is available in the open literature. The computed turbulent Reynolds stresses from DES are lower than RANS within the boundary layer at the leading edge of the suction side. It is argued to be due to the premature switching to less dissipative LES mode within boundary layer. The DDES gives comparable values to RANS, as an expected outcome. It is observed that for the cases with the mild separation, although DDES works in correct fashion in line with the basic concept of treating the whole of the boundary layer in RANS mode. However, the original DES may perform better than the DDES due to lower dissipation characteristics. The DES results on the suction side in the wake-region are encouraging and comparatively better than DDES, despite its switching problem.