Abstract
Lattice Boltzmann method (LBM) simulations were performed to capture the long-period dynamics within the wake of a realistic DrivAer fastback model with stationary and rotating wheels. The simulations showed that the wake developed as a low-pressure torus regardless of whether the wheels were rotating. This torus shrank in size on the base in the case of rotating wheels, leading to a reduction in the low-pressure footprint on the base, and consequently a 7% decrease in the total vehicle drag in comparison to the stationary wheels case. Furthermore, the lateral vortex shedding experienced a long-period switching associated with the bi-stability in both the stationary and rotating wheels cases. This bi-stability contributed to low-frequency side force oscillations (<1 Hz) in alignment with the peak motion-sickness-inducing frequency (0.2 Hz).
Highlights
IntroductionSimplified square-back automotive models such as the Ahmed body [1] and the Windsor body [2] have been found to develop aperiodic vortex shedding wherein the shedding of vortices favors one side of the vehicle over long time periods [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]
Lattice Boltzmann method (LBM) simulations were performed to study the influence of wheel rotation on the wake dynamics for the realistic DrivAer fastback model
When the wheels were rotating, the size of the low-pressure torus became smaller and less pressure loss occurred within the torus, leading to a reduction in the turbulence intensity in the underbody of the vehicle as well as an overall drag reduction by 7% compared to the stationary wheels case
Summary
Simplified square-back automotive models such as the Ahmed body [1] and the Windsor body [2] have been found to develop aperiodic vortex shedding wherein the shedding of vortices favors one side of the vehicle over long time periods [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18] This aperiodic wake-switching behavior is typically referred to as bi-stability. Passive flow control techniques, such as the addition of a cavity on the vehicle base, successfully suppress the low-frequency switching of the bi-stability, reducing the vehicle drag [13]. The lack of a realistic representation of production cars when using simplified automotive models has limited an effective extrapolation of such flow control studies to production vehicles
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