Recent Advances in Wake Dynamics and Active Drag Reduction of Simple Automotive Bodies

This is a compendium of recent progresses in the development of wake dynamics and active drag reduction (DR) of three-dimensional (3D) simple automotive models, largely focused on the generic Ahmed body. It covers our new understanding of involved instabilities, predominant frequencies, pressure distribution, and unsteady flow structures in the high- (12.5 deg < φ < 30 deg) and low-drag (φ > 30 deg) bodies and the square-back body (φ = 0 deg), where φ is the rear slant angle of the body. Various DR methods and their performances are reviewed, including open- and closed-loop controls along with machine-learning control (MLC). The involving DR mechanisms, net saving, and efficiencies are discussed. Comments are made for the areas that deserve more attention and future investigation.