An investigation on the switching of asymmetric wake flow and the bi-stable flow states of a simplified heavy vehicle

Abstract

This study investigates the effect of aspect ratios (Ra*) on the wake bi-stability behind the GTS model using improved delayed-detached eddy simulation (IDDES) at a Reynolds number of 2.7×104. Eight cases with Ra* in the range of Ra*∈[0.5, 2.0] have been considered to investigate the asymmetric wake flow and the corresponding aerodynamic response. The primary objective of this study is to reveal the mechanism of the Ra* effects on the GTS’s flow topology, asymmetric wake flow and the bi-stable flow switching process. The accuracy of the numerical method has been validated by comparing the recirculation bubble, vortex core and aerodynamic drag with those obtained from the previous large-eddy simulation study and the water channel experiment. The results show that three typical flow topologies (FT-I, FT-II and FT-III) are classified according to the drag coefficient and the length relation between the vertical and horizontal recirculation region. The vertical and horizontal asymmetric characteristics can be transformed between two adjacent flow topologies. Moreover, a switching process of the bi-stable wake flow is also observed as Ra* is equal to 0.71. Additionally, the ground motion can reverse the dominated flow state and inhibiting the corresponding switching process.

Keywords

• aspect ratio
• bi-stable flow
• IDDES
• simplified heavy vehicle
• switching process
• wake asymmetry