Investigation of the link between vehicle underbody and base unsteady wake aerodynamics

The unsteady flow around a squareback automotive body at $R{e}_h$ of approximately $7.4\times 10^5$ is investigated using a Large Eddy Simulation. The study is conducted with rotating wheels and a moving ground plane and is shown to be in strong agreement with the mean flow fields of similar experimental datasets. Proper Orthogonal Decomposition, Spectral Proper Orthogonal Decomposition, and spectral analysis of the time-resolved pressure fields on the model surfaces are used to reveal spatial and temporal interactions in the wake and underbody flow. The salient underbody flow features determined are lateral and streamwise motions between the rear wheels and a more complex shedding interaction from the front wheels. The rear wake exhibits a dominant lateral flapping motion and is shown to correlate to an underbody lateral mode. This is further seen through conditional averaging of the underbody and rear wake structures, showing a concurrent lateral bias. This study demonstrates a link between rear-wheel-to-base unsteady flow features, highlighting the importance of considering these interactions in future vehicle aerodynamic studies.