Race Car Aerodynamics Simulation and Transmitted Tire Reaction Forces

Abstract

ABSTRACT: Often in Computational Fluid Dynamics integral forces and restoring moments are calculated, but the location where they should be applied may not always be clear. This is because the location is not intuitive: it is dependent on the vehicle’s velocity and its orientation (e.g. sideslip angle). A technique has been developed to translate the aerodynamic forces to the reaction forces on the vehicle’s tires. In this study, CFD simulation is performed with a 7.5° yaw to look at the effect of cornering. To understand aerodynamic effect on vehicle dynamics one must know the location at which this force is applied. This location is commonly called the center of pressure (COP), but more precisely it should be called the COP-Axis because the force is applied along a line-of-action rather than a point. This paper illustrates that. After knowing the aerodynamic forces and the COP-Axis, the reaction force at each tire is calculated. First, the problem is modeled up as a single force with 4 tires. As one can guess, having 4 tires is over-constraining so this is a static indeterminant problem. In 3D there are 6 equations but now we have 12 unknowns. In order to solve the static indeterminant problem it is modelled up as a deformable body. By taking material property into consideration, the percentage of load that’s transferred to each tire is affected. Using the process described in this paper, reaction forces from each tire have been successfully computed and one can see their effect from aerodynamic loads.