Unsteady Aerodynamical Forces by Interference of Two Bluff Bodies Moving Closely : On Unstable Phenomenon of Automobile Running at High Speed

Abstract

It is a familiar phenomenon that a small car may be attracted toward a large one when the small one is passed by the large one. It is the purpose of this study to clarify this attraction phenomenon from an aerodynamical point of view. The unstesdy aerodynamical forces generated by an interference of two bluff bodies moving closely are measured by the wind-tunnel-balance. And changes of the yawing moment, the lift and the drag are determined at different speeds, different spacings between the two bodies and different body scales. Moreover, equations of motion for the vehicle are numerically solved by using experimental results with the unsteady aerodynamical forces. The behavior of the vehicle in this unstable situation is discussed for different handling characteristics.