Effects of Rear Slant Angles on the Bi-Stable Behavior of the Ahmed Body

The bi-stable phenomena of the Ahmed model were experimentally studied at different rear slant angles (31.8 °, 42 °, 50 °, 60 °, 75 °, 90°) and different Reynolds numbers (9.2 × 10⁴, 1.84 × 10⁵, 2.76 × 10⁵). The analysis of pressure gradients both on the base and slant indicate that no bi-stable phenomena were observed at different Reynolds numbers when the slant angle was less than or equal to 50°. However, for the rear slant angles greater than or equal to 60°, the pressure gradients consistently shift between two preferred values at various Reynolds numbers, indicating the presence of bi-stable behavior in the spanwise direction. Therefore, the critical angle for the appearance of bi-stability in the Ahmed model lies within the range of 50° to 60°, and the existence of bistable behavior remains unaffected by the Reynolds number. As the slant angle increases, the switching rate decreases significantly until the angle is greater than 60°. Furthermore, with an increase in Reynolds number, the switching rate exhibits a monotonic decrease for most angles, except at 75° and 90°. The rate of decrease, however, diminishes for larger angles. Notably, at both 75° and 90°, the influence of Reynolds number on the switching rate is less pronounced.