Aerodynamic forces that act on a vehicle play a critical role in impacting the
vehicle longitudinal dynamics, particularly stopping distance and time during
vehicle braking. Currently, many vehicles use a rear spoiler to enhance the
vehicle aerodynamic performance. In vehicles equipped with an active rear
spoiler, a mechanism is used to control the spoiler angle of attack, based on
various inputs and parameters. This article investigates the impact of an active
rear spoiler, with a variable angle of attack, on both the vehicle aerodynamic
forces and longitudinal braking dynamics, such as braking stopping distance and
time. A two-dimensional (2D) computational fluid dynamics (CFD) model, using
ANSYS-Fluent®, is employed to estimate the impact of the angle of attack of the
rear spoiler on the vehicle aerodynamic forces (lift and drag forces) for
comparison with a vehicle lacking a spoiler. Furthermore, the CFD results are
used as inputs in a realistic vehicle braking mathematical model to estimate the
vehicle stopping distance and time at different spoiler angles of attack, and
the obtained results are compared to the case of the vehicle that is not
equipped with a spoiler. The proposed vehicle model, which includes the vehicle
aerodynamic forces, is simulated using MATLAB/Simulink®. The simulation results
demonstrate that the vehicle rear spoiler has a clear impact on the vehicle
braking distance and time, especially at high vehicle speeds. Based on the
simulation results, novel 2D maps, which relate the vehicle stopping distance
and time to the angle of attack of the vehicle rear spoiler, are presented.
These maps can be used as a good basis for estimating the optimal spoiler angle
of attack for vehicle braking at different initial speeds and, hence, can
provide significant help in the design of an optimal braking system controller
for the vehicle.
