Experimental investigation of the flow features around an elliptical Ahmed body

Abstract

The standard Ahmed body (SAB) with a rectangular rear end is a simplified, canonical bluff body geometry that shares similarities with generic road vehicles. It is known to produce flow separations and strong vortices at the rear end. The aerodynamic performance of vehicles is significantly affected by such three-dimensional flow structures. This work proposed a modified Ahmed body with an elliptical rear end called the elliptical Ahmed body. The study examines in detail the near-field characteristics of the flow over the elliptical Ahmed body at a slant angle of 25° with a low Reynolds number of [Formula: see text] based on the model height. The principal flow features are analyzed using time-resolved and standard particle image velocimetry. The time-averaged and time-resolved analyses revealed a fully detached flow at the rear end that eliminated the slant separation bubble. Furthermore, a significant wake flow restructuring is found to curb the lower recirculation bubble and shift the upper recirculation bubble toward the slant surface. Thus, the elliptical curvature shifts the critical slant angle of 30° in SAB to 25°, which indicates transformation of the high-drag flow structures into low-drag. Several distinct Strouhal numbers are found over the slant surface (St = 0.55–0.88), which are higher than that of the SAB, while no significant change is found in the wake region (St = 0.23–0.50). In addition, the effect on coherent structures is evaluated using proper orthogonal decomposition and dynamic mode decomposition, which shows a considerable difference between the standard and elliptical Ahmed body wake structures. The results of this investigation show that body modification of the Ahmed body using elliptical curvature at the rear end can significantly affect the overall flow features and help improve the aerodynamic performance of the vehicles.