Aerodynamic Sensitivity Analysis of Tire Shape Factors 2020-01-0669
It is well known that the wheels and tires account for approximately 25% of the overall aerodynamic drag of a vehicle. This is because the contribution of the tires to aerodynamic drag stems from not only aerodynamic drag itself directly caused by exposure to the main flow (tire CD), but also from aerodynamic drag indirectly caused by the interference between tire wakes and the upper body flow (body CD). In the literature, as far as the authors are aware, there have been no reports that have included the following all four aspects at once: (1) CD sensitivity to detailed tire shape factors; (2) CD sensitivity differences due to different vehicle body types; (3) CD sensitivity for each aerodynamic drag component, i.e., tire CD and body CD; (4) Flow structure and mechanism contributing to each aerodynamic drag component. The purpose of this study was to clarify CD sensitivity to tire shape factors for tire CD and body CD considering two different vehicle body types, sedan and SUV. In wind tunnel testing, many tire configurations were prepared for a parametric study. Detailed shape factors of each tire were three-dimensionally measured by laser beam scanning in the test section taking into account tire deformation. For decomposing the aerodynamic drag components, measurements were made of CD and also the pressure at the vehicle base in the tests. For analyzing the mechanism causing CD differences, flow fields were obtained by measuring the surface pressure on the test vehicles and also the spatial pressure and velocity were measured at cross sections of the body side. Multiple regression analyses clarified CD sensitivity to tire shape factors for tire CD and body CD with respect to the sedan and SUV body types. This study revealed high CD sensitivity factors that were independent of exterior styling. Furthermore, analyses of computational fluid dynamics (CFD) simulation results identified the flow fields contributing to each aerodynamic drag component, tire CD and body CD.