A Study of an Active Rear Diffuser Device for Aerodynamic Drag Reduction of Automobiles 2012-01-0173
The goal of this study is to develop an actively translating
rear diffuser device to reduce the aerodynamic drag experienced by
passenger cars. The feature of this device is hidden under the rear
bumper ordinarily not to ruin the external design of the car and
slips out backward under the high-speed driving condition. By this
study, a movable arc-shaped semi-diffuser device is designed to
maintain the streamlined automobile rear underbody configuration.
It's installed under the rear bumper of a passenger car.
Seven types of rear diffuser devices whose positions, slid out
lengths and widths are differing with the basic shape installed in
the rear bumper section of a passenger car and performed
Computational Fluid Dynamics (CFD) analyses under rotating wheel
and moving ground conditions. The main purpose of this study is
that explains the aerodynamic drag reduction mechanism of a
passenger car via an actively translating rear diffuser device at a
high speed driving condition. The base pressure of the rear surface
of passenger car is increased by install the rear diffuser device,
because it prevents the low pressure air coming through the
underbody from directly soaring up to the rear surface of the
trunk. At the same time, it increases a diffusing effect to
underbody flow which lowers the velocity and raises the pressure,
bringing about an aerodynamic drag reduction.
Finally, the automobile aerodynamic drag is reduced about an
average of more than 4% in 450 mm length with the base
configuration. And also maximum 7% of drag reduction accomplished
changing the shape of the rear diffuser device into various types.
At the end, the diffuser device was applied to the YF SONATA
developed and produced by the Hyundai Motors Company. The drag
reduction was achieved up to 5.2% in the speed range of 80 km/h ~
120 km/h. In addition, owing to generation of negative lift by the
diffuser device, it is expected the driving stability improved in
high speed condition.