Wheel Flow Instabilities and Drag Control in Automotive Aerodynamics: A Comprehensive Review

This review addresses four key themes in automotive aerodynamics: flow instability in the wheel region, the aerodynamic characteristics of rims, the aerodynamic behavior of tires, and drag reduction strategies based on flow control around the wheels. The wheel region, comprising the tire, rim, and adjacent aerodynamic components, typically represents the major source of vehicle drag owing to the inherently complex flow generated by wheel rotation, tread geometry, and rim design, which gives rise to flow separation, vortex shedding, and turbulence. Drawing on a broad body of experimental and numerical research, this review elucidates the mechanisms governing such dynamics, and considers drag mitigation techniques, including biomimetic surface treatments and multi-element flow control concepts. Particular emphasis is placed on enclosed-spoke rims, rim-edge enclosures, and non-smooth tire microstructures, which have consistently demonstrated notable drag reduction potential. The review further identifies critical shortcomings in current research, most notably the lack of quantitative analyses of aerodynamic energy losses and the absence of integrated optimization strategies that jointly address tire, rim, and fender design.