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The aerodynamic performance of new vehicles is commonly determined using computational fluid dynamics (CFD) and wind tunnel tests. The final assessment is carried out by actual running tests. In particular, ideas regarding fuel consumption improvement that relate to components for the reduction of the coefficient of drag (CD) value are evaluated by coast-down tests. However, a difference often exists between the component's efficiency between wind tunnel tests and coast-down tests. Therefore, we focused on the efficiency of an air-dam spoiler in reducing CD values. A comparison was made between the aerodynamic effect of the air-dam spoiler in wind tunnel and coast-down tests in terms of the CD value and the wake structure behind the vehicle. To determine the relationship between the CD value and the wake structure behind the vehicle, we measured vehicle speed, wind velocity and direction, vehicle height, and pressure distribution on the back door.

This paper describes a system for measuring unsteady pressure at up to 256 spatial points and at frequencies up to 300 Hz. The system consists of commercially available equipment for measuring steady pressures. It is based on the use of electronically scanned pressure (ESP) sensors, 16 A/D converters, and a personal computer to control the whole system and acquire data. The signal outputs through the tubes connecting the pressure taps and the ESP sensors are compensated, as are the phase delays between the scanned signals and the gain variation. A 1/5 scale model of a sedan was used in this experiment. The passenger car model was placed in a wind tunnel equipped with a moving belt, which was operated at the same speed as the uniform flow in the wind tunnel. Pressure measurements were obtained at 252 points in a plane behind the model perpendicular to the uniform flow. Measurements were made with the belt turned on and off.