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As speed of ground vehicle increases, there are increased concerns on the aerodynamic drag reduction of ground vehicle. Recently, synthetic jet is emerging as a promising active flow control technology for aerodynamic drag reduction. In this paper, we performed an experimental parametric study on synthetic jet for aerodynamic drag reduction of Ahmed model. Synthetic jet array is constructed by twelve synthetic jet actuators, and installed on two kinds of Ahmed models, of which slant angles are 25° and 35°. The jets are emanated between the roof and the rear slant surface. Jet angle, momentum coefficient, and driving frequency are changed to assess the effect of synthetic jet array on aerodynamic drag. To quantify the effect of synthetic jet, the aerodynamic drag and rear surface pressure are measured and analyzed. From the result, the effect of synthetic jet actuation on aerodynamic drag differs according to the slant angle of the body.

Exterior shape of automobile can be represented by shape function through this study so that aerodynamic shape parameters can be easily controlled and changed. Also ordinary geometric information can be extracted easily from shape function model by simple calculations. It is possible to predict the aerodynamic performance of functional virtual car models which are transformed continually by developing automated program in initial design stage that includes all of above process. Innovative vehicle design process with exterior design guide will be proposed for stylist, engineer and packaging department in order to achieve low aerodynamic drag and high fuel efficiency targets.

A series of experiments and computational analysis were carried out on the flow around a bluff body. Some non-streamlined ground vehicles, buildings and pipelines near to the ground could encounter very dangerous situations because of the unsteady wind loading caused by the periodic vortex shedding behind the bluff body. A two-dimensional bluff body model was used to simulate flow in the wake region. Spectral analysis of the velocity profiles in the underbody region was also used to examine the influence of the underbody flow in the wake region. By using a flow visualization technique, the critical gap height and the separation line on the ground were investigated for various gap heights and boundary layer thicknesses. Additionally, the 2-D Incompressible Navier-Stokes equation with an ε - SST (Strain Shear Stress Transport) turbulence model was used for comparison with experimental results.

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.