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Aerodynamic technologies for light-duty vehicles were evaluated through full-scale testing in a large low-blockage closed-circuit wind tunnel equipped with a rolling road, wheel rollers, boundary-layer suction and a system to generate road-representative turbulent flow. This work was part of a multi-year, multi-vehicle study commissioned by Transport Canada and Environment and Climate Change Canada, and carried out in cooperation with the US EPA, to support the evaluation of light-duty-vehicle greenhouse-gas-emission regulations. A 2016 paper reported drag-reduction measurements for technologies such as active grille shutters, production and custom underbody treatments, air dams, ride height control and combinations of these. This paper describes an extension to that work and addresses vehicle aerodynamics in three ways.

Road vehicles in the real world experience aerodynamic conditions that might be unappreciated and omitted in wind-tunnel experiments or in numerical simulations. Precipitation can potentially have an impact on the aerodynamics of road vehicles. An experimental study was devised to measure, in a wind tunnel, the impact of rain on the aerodynamic forces of the DrivAer research model. In this study, a rain system was commissioned to simulate natural rain in a wind-tunnel environment for full-scale rain rates between about 8 and 250 mm/hr. A 30%-scale DrivAer model was tested with and without precipitation for two primary configurations: the notch-back and estate-back variants. In addition, mirror-removal and covered-wheel-well configurations were investigated. The results demonstrate a distinct relationship between increasing rain intensities and increased drag of the model, providing evidence that road vehicles experience higher drag when travelling in precipitation conditions.