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Recently, rider comfort at highway driving has become an important issue in the performance improvement of motorcycles. Comfort includes windbreak, pressure on the rider, wind noise, visibility, and steering characteristics. However, most of these factors cannot be analyzed conventionally. Therefore we used CFD (Computational Fluid Dynamics) to examine the rider’s airflow environment. The environment of a rider on a motorcycle is an open space, very different from the passenger environment in an automobile. There are many airflow paths in a motorcycle with a cowl and a windscreen; thus, airflow behavior is constituted with a delicate balance. Though wind tunnel tests can give us an outline of airflow, CFD is a useful way to visualize the airflow of the rider’s environment and clarify the details. As the results, a lot of helpful knowledge was obtained for the development of new motorcycles.

In CFD (Computational Fluid Dynamics) verification of vehicle aerodynamics, detailed velocity measurements are required. The conventional 2D-PIV (Two Dimensional Particle Image Velocimetry) needs at least twice the number of operations to measure the three components of velocity ( u,v,w ), thus it is difficult to set up precise measurement positions. Furthermore, there are some areas where measurements are rendered impossible due to the relative position of the object and the optical system. That is why the acquisition of detailed velocity data around a vehicle has not yet been attained. In this study, a detailed velocity measurement was conducted using a 3D-PIV measurement system. The measurement target was a quarter scale SAE standard vehicle model. The wind tunnel system which was also designed for a quarter scale car model was utilized. It consisted of a moving belt and a boundary suction system.