Simulation of nonlinear performance of a top fuel dragster race car
Castillo, David Hernandez
Spanos, Pol D.
Doctor of Philosophy
In order to analyze and increase the performance of a top fuel dragster, a dynamic model of the car was developed in this thesis. The drag racing car is moving mainly in a rectilinear/one dimensional mode, nevertheless, a five-degree-of-freedom model was needed to properly capture its dynamic behavior. This is a 2D model of the car dynamics in the vertical plane. Longitudinal, vertical, and pitching chassis motions were considered, as well as drive-train dynamics. The aerodynamics of the car, the engine characteristics, and the force due to the combustion gases were incorporated in the model. Further, the rear tires deflection due to the torque and the vertical load was included in the analysis, considering the effect of the angular speed on it. Also, a simplified model of the traction characteristics of the rear tires was developed. With this model, the traction is calculated as a function of the slip ratio and the speed. Since the diameter of the dragster rear tires is not constant, but increases with the angular speed, the angular momentum equation was considered. This leads to deriving an equivalent mass moment of inertia of the rear tires. This moment of inertia is a function of the angular speed. The model not only considered the instantaneous radius of the tires, but the rate of deformation was also taken into consideration. In this manner, the torque applied to the rear tires, and the angular acceleration produced on them, were related by the simple torque-angular acceleration equation of rigid body dynamics. The complete model to analyze the dynamic of the vehicle involves a set of nonlinear, coupled differential equations of motion, which were numerically integrated using a digital computer. Several simulation runs were made to investigate the effects of the aerodynamics, and the engine initial torque in the performance of the car. The simulation results show that the model captured to a significant degree the dynamic behavior of the dragster. They also suggest that a reduction in the elapsed time during a race can be possible under appropriate conditions. The proposed dynamic model of the dragster can be used to improve the aerodynamics, the engine and clutch set-ups of the car, and to possibly facilitate the redesign of the dragster. This model can be adapted to perform analyses of other types of drag racing vehicles, such as pro-stock cars and motorcycles. Used in conjunction with accurate and more complete data available to racing teams, the model can be quite useful in improving the performance of current top fuel dragsters and "funny" cars.
Applied mechanics; Automotive engineering; Mechanical engineering