Research on Aerodynamic Drag Reduction by Vortex Generators
Masaru KOIKE* Tsunehisa NAGAYOSHI* Naoki HAMAMOTO*

Abstract
One of the main causes of aerodynamic drag for sedan vehicles is the separation of flow near the vehicle’s rear end. To delay flow separation, bump-shaped vortex generators are tested for application to the roof end of a sedan. Commonly used on aircraft to prevent flow separation, vortex generators themselves create drag, but they also reduce drag by preventing flow separation at downstream. The overall effect of vortex generators can be calculated by totaling the positive and negative effects. Since this effect depends on the shape and size of vortex generators, those on the vehicle roof are optimized. This paper presents the optimization result, the effect of vortex generators in the flow field and the mechanism by which these effects take place. Key words: Body, Aerodynamics, Aerodynamic Devices, Flow Visualization, Computational Fluid Dynamics (CFD)

1. Introduction
To save energy and to protect the global environment, fuel consumption reduction is primary concern of automotive development. In vehicle body development, reduction of drag is essential for improving fuel consumption and driving performance, and if an aerodynamically refined body is also aesthetically attractive, it will contribute much to increase the vehicle’s appeal to potential customers. However, as the passenger car must have enough capacity to accommodate passengers and baggage in addition to minimum necessary space for its engine and other components, it is extremely difficult to realize an aerodynamically ideal body shape. The car is, therefore, obliged to have a body shape that is rather aerodynamically bluff, not an ideal streamline shape as seen on fish and birds. Such a body shape is inevitably accompanied by flow separation at the rear end. The passenger car