Impact of Rear Spoiler on Vehicle Braking Longitudinal Dynamics

During vehicle braking, friction forces generated on the vehicle tires and the vehicle resisting aerodynamic forces play a critical role that impact the vehicle’s longitudinal braking dynamics such as stopping distance and time. These forces are mainly the tires’ braking and rolling resisting forces, vehicle lift, and drag forces. The vehicle aerodynamic forces cannot be neglected due to their impact on the vehicle’s longitudinal dynamics, especially at high vehicle speeds. This article investigates the impact of the vehicle’s rear spoiler on both vehicle aerodynamic forces and longitudinal dynamic, such as stopping distance and time. A computational fluid dynamics (CFD) model using ANSYS-Fluent® is employed to precisely estimate the vehicle’s aerodynamic forces in the case of a vehicle without and with a rear spoiler. The two-dimensional (2D) CFD model resolves the airflow all around the vehicle and rear spoiler precisely and allows to compute the drag and lift forces exerted on the vehicle and the rear spoiler. A realistic vehicle braking longitudinal dynamic mathematical model is introduced. The model takes into consideration a realistic random uncertainty that normally exists in the tires’ adhesion and rolling coefficients and at the same time takes the vehicle’s aerodynamic forces into account. The proposed model is simulated using MATLAB/Simulink® with realistic vehicle parameters for the cases of the vehicle without and with the spoiler. The simulation results show the noticeable impact of the vehicle’s rear spoiler on both vehicle stopping distance and time, especially at high vehicle speeds. They also prove the validity of the proposed model and highlight the potential benefits of equipping the vehicle with a rear spoiler in braking control system design.