A Study on Unsteady Aerodynamic Characteristics Acting on Front Fenders of Motorcycles during Steering Motion 2022-01-0897

Compared to a four-wheeled vehicle, a two-wheeled vehicle’s steering motion has a greater influence on roll behavior as well as yaw. On the other hand, the effect of the aerodynamic characteristics of the front fender on the steering moment has not been clarified. Therefore, a sensory evaluation test was important to know its influence on actual vehicle behavior. In this study, a basic technology to understand the aerodynamic characteristics of the front fender that affect the vehicle behavior of motorcycles was developed. In addition, CFD analysis was used to analyze the generation mechanism of the aerodynamic characteristics during the steering motion. First, the aerodynamic characteristics during the steering motion on the actual vehicle were measured using the wind tunnel facility. Next, the tests in the wind tunnel were reproduced in the CFD analysis using a moving and deforming mesh. As a result of verification of calculation accuracy, it was confirmed that the CFD analysis accurately reproduced the aerodynamic characteristics of the steering moment acting on the front fender during steering motion. In addition, the relationship between the magnitude of the vehicle behavior when a disturbance input was applied around the steering axis and the steering moment of the front fender obtained using the CFD analysis was confirmed. As a result, it was found that the closer the coefficient of the damping term of the moment was to zero, the smaller the roll motion when a disturbance is applied to the steering system tends to become. This suggests that the damping term of the steering moment acting on the front fender is one of the factors affecting the vehicle behavior of motorcycles. The CFD analysis revealed that the damping term of the steering moment is generated by the time difference between the separation of the airflow at the tip of the front fender and its aerodynamic action behind the front fender.