Investigation of the wake flow of a simplified heavy vehicle with different aspect ratios

Abstract

This study numerically investigates the effects of aspect ratios on the wake flow of a simplified ground transportation system (GTS) model using improved delayed detached-eddy simulation (IDDES) at a Reynolds number of 2.7 × 104. The aspect ratio Ra* ∈ [1.0, 2.0] is defined as the ratio of the height (H, variable) to the width (W, constant) of the GTS. The primary purpose of this work is to identify the relationship between the aspect ratio and the wake flow topology. The accuracy of the IDDES method has been validated by comparing the recirculation bubble configuration, vortex core position, velocity profiles, and aerodynamic drag of the baseline model (Ra* = 1.41) with those obtained from the previous large-eddy simulation study and the wind tunnel experiment. The results show that three typical flow states are observed in the near-wake region for various aspect-ratio cases. The aerodynamic drag increases by 4.60% and 2.06% for the aspect-ratio value equal to Ra* = 2.0 and Ra* = 1.8 (flow state II) and reduces by 6.75%, 7.37%, and 7.98% for the models with the aspect-ratio value of Ra* = 1.15, Ra* = 1.05, and Ra* = 1.0 (flow state III) compared to the aerodynamic drag of the baseline model with the aspect-ratio value of Ra* = 1.41 (flow state I). The dominant shedding frequency of the turbulent wake flow is identical for the aspect-ratio cases when the corresponding wake topology stays in the same flow state. The flow state acts as the substantial factor, which has an essential influence on the GTS's wake flow and its inducing aerodynamic response.