Effects of Rear Slant Angles on the Flow Characteristics of the Ahmed Body by IDDES Simulations 2018-01-0720

The present study aims to investigate the effects of the several rear slant angles, φ = 25°, 30°, 32°, 33° and 35°, on the wake characteristics downstream of the Ahmed body because the angle of the rear window plays an important role in the flow characteristics. This work presents numerical simulations using ISIS-CFD flow solver which is developed by Centrale Nantes and CNRS. The turbulence model used is an hybrid RANS-LES model: the Improved Delayed Detached Eddy Simulation (IDDES). Detailed discussions of the flow features are provided using time-averaged streamlines, vorticity contours, turbulent kinetic energy contours and an iso-surface of l₂. Drag and lift coefficients are also presented. In the symmetry plane, three critical flow points, which correspond to foci of separation and saddle point in the wake of the Ahmed body, and the focus of separation over the slanted surface are presented. When the slant angle increases, these critical points move near the Ahmed body before moving away the model when the slant angle is higher than 33°. For the slant angle φ = 35°, a low drag configuration is predicted while for the other slant angles, a high drag flow configuration is predicted where two C-pillars vortex are present. These vortices move away the model when the slant angle increases.