Effects of rear slant angles on the flow characteristics of Ahmed body

Ahmed body is a simplified vehicle model which retains important features of real ground vehicles. Present study aims to investigate effects of rear slant angles (alpha = 25 degrees, 30 degrees and 35 degrees) on time-averaged and instantaneous flow characteristics downstream of the Ahmed body because angle of the rear slanted surface considerably affects the flow characteristics. The particle image velocimetry (PIV) technique is employed to measure the flow field in the symmetry plane z = 0 downstream of the Ahmed body. Demonstration and detailed discussions of the flow features are provided using time-averaged velocity vectors, streamlines, vorticity and TKE contours. Three critical flow points are revealed in the wake downstream of the Ahmed body. Namely, they are focus point 1 (F-1), focus point 2 (F-2) and saddle point (S). Variations in slant angle cc cause shift in the locations of these critical flow points. Effects of change of slant angle cc on each critical flow point vary according to their locations in the wake. Instantaneous vorticity contours and spectral analysis of the velocity field are also provided. As a result of the spectral analysis, a single dominant frequency location is only detected for alpha = 25 degrees, on the other hand two dominant frequency locations are detected for alpha = 30 degrees and 35 degrees in the wake. Mean stream-wise and vertical velocity components are compared with available data in the literature. Although there are some discrepancies between the present and previous results at certain locations in the flow field, general agreement between these results is reasonably good when taking the difference between Reynolds numbers of the two studies into account. (C) 2014 Elsevier Inc. All rights reserved.