LES Study on the Aerodynamic Stability of Sedan-Type Road Vehicle

Abstract

In this paper, in order to investigate a fundamental mechanism of a high-speed aerodynamic stability of sedan-type road vehicle, Large-Eddy Simulations on two simplified vehicle models are conducted. The objective vehicle models were simplified from the real sedan-type road vehicle and they have the same characteristics of the shapes as the original road vehicles. In the numerical simulations, interaction between vehicle motion and the aerodynamics is treated by a moving boundary technique with the ALE method. The target vehicle motion is a pitch motion, which was indicated as the related factor of the vehicle's running stability. Before the simulations with dynamic vehicle motion, steady and unsteady flow characteristics around each model in stationary conditions are extracted by the numerical simulations. The slight different shapes of the vehicle model generated a significantly different flow structure around the vehicles. The quasi-stationary responses of the aerodynamics are also simulated on two different steady pitch conditions. Then, in nonstationary conditions with forced pitch oscillation, the interaction between the vehicle motion and the aerodynamics are investigated. The unsteady aerodynamic moment is decomposed to approximation function by the least-square method. Considering each decomposed factor, the vehicle model with high running stability has been considered as a stable model for the pitch motion in the evaluations of stability based on a quasi-stationary manner. However, regarding the non-stationary component, the additional mass effect is rather high in the high stability model. Aerodynamic damping factor, which is another nonstationary component, has significant intensity in both two models though their intensities are the same level with each other.