Correlation between Aerodynamic Drag Found on CFD Simulations, Wind Tunel Testing and CoastDown Testing

It is known that aerodynamics influences directly on a vehicle´s fuel consumption, especially at speeds above 45-60km/h, where it becomes the main parasitic loss. With increasing pressure on automakers to develop more efficient vehicles, aerodynamics is playing a crucial role in the goal of saving vehicle´s fuel. Usually aerodynamic development starts in the early stages of the project, responsible engineer works together with designers and body/ergonomics engineers, using CFD simulations as tool. At certain point in the development time line, full scale or scaled models are manufactured and tested in wind tunnels, where vehicle gets a refinement on its external aerodynamics. However, the measurement of aerodynamic drag which is effectively used for homologated vehicle´s fuel consumption is done by coastdown testing. This paper shows a correlation between results from CFD simulations and results measured from wind tunnel and coastdown testing. Same vehicle was used in all tests, divided in two stages. The first one used the vehicle exactly as it is when left production assembly lines and in the second step the same vehicle was equipped with an aerodynamic kit, which aims to reduce its drag and hence its fuel consumption.