Analysis of Effective Configuration Parameter for Reducing Aerodynamic Drag of Bluff Body such as Vehicle. 1st Report, Aerodynamic Drag and Wake Structure of Box Type Vehicle.

This paper analyzes experimentally the influence of the geometrical configuration on the aerodynamic drag using a bluff body such as a box-type (fastback) vehicle. For a box-type vehicle, the aerodynamic drag depends on the angle of the front window and the rear window. Therefore, these angles were selected as the configuration parameters. By changing the window angle and the ratio of the model length to the bending window position, the aerodynamic drag characteristics were investigated. As a result, it is found that, the aerodynamic drag decreases at the front window angle of 20∼30°and increases drastically at the rear window angle of 30°when the ratio of the model length to the bending rear window position is more than 0.2. On the other hand, it is also found that the wake of the box-type vehicle consists of the arch vortex on the rear window and the trailing vortices behind the rear window, by means of the flow visualization and the velocity vector distribution. Based on understanding the wake structure, it is clarified that the aerodynamic drag which increases drastically at the rear configuration is caused by the arch vortex on the rear window.