Aerodynamic stability of road vehicles in dynamic pitching motion

Abstract

The main object of the present study is to investigate numerically the mechanism of aerodynamic damping of pitching oscillation in sedan-type vehicles. The transient numerical solver employed is based on the Large Eddy Simulation (LES) method. Whilst, the Arbitrary Lagrangian-Eulerian (ALE) method was used to realize the vehicle motion during dynamic pitching and fluid flow coupled simulations. Validation of the numerical method was done by comparing the flow structures obtained from the LES to the corresponding flow structures observed in the wind tunnel measurements. Two vehicle models with basic sedan-type automobile shape were created to study the influences of upper body geometry on the aerodynamic pitching stability of sedan-type vehicle. In addition, the credibility of modeling of automotive aerodynamics by simple bluff body models was verified. For the sedan-type models investigated, the trailing vortices that shed from the A-pillar and C-pillar edges were found to produce the opposite tendencies on how they affect the aerodynamic pitching stability of the models. In particular, the vortex shed from the A-pillar edge tended to enhance the pitching oscillation, while the vortex shed from the C-pillar edge tended to suppress it. Hence, the vehicle with rounded A-pillar and angular C-pillar exhibited a higher aerodynamic damping than the vehicle with the opposite A-and C-pillars configurations. The aerodynamic damping mechanism has been proposed based on the results of flow visualization on the phase-averaged flow properties.

A Novel Shape-Adjustable Surface and Its Applications in Car Design

“…Its cross section covered 5 times the length upstream and 10 times the length downstream of the CAD vehicle model, 4 times the width on both left and right sides, and the height was 5 times the height of the model. The corresponding blockage ratio was about 1.12% according to our measurements, which is within the scope of 5% in typically accepted automobile aerodynamic testing (see [29]). The triangle mesh was set as 10 mm, and the hybrid tetrahedron was 10-200 mm.…”

“…In the long-term research of Cheng et al [27][28][29], they built various CAD car body models with different complexity to explore the influence of A-pillar and C-pillar of automobiles of different shape (rounded or angular) on driving pitching stability. In their research in 2014 [29], they used the large eddy simulation method on two CAD models with full details; they drew the conclusion that the vortex shed from the A-pillar edge results in a destabilizing tendency while the vortex shed from the C-pillar edge results in a stabilizing tendency. Hassan et al [30] reduced the drag coefficient by nearly 10% by optimizing the angle of departure and the shape of the Rear body diffuser in a racing car CAD model.…”

Large Eddy Simulation of the Flow-Field around Road Vehicle Subjected to Pitching Motion

“…Aschwanden et al (2008) used the wind tunnel to study the ride height change of the race cars, and found that the motion aerodynamic caused greater effects on the simplified race car model in the simulated movement. Cheng et al (2013) studied the influence of different combinations of A, C pillar to the aerodynamic stability of the vehicle, and found the importance of the proper shaping of A-pillar and C-pillar to control the vehicle body pitching oscillation. However, their researches mainly focused on transient aerodynamics force to the stability of vehicle, the mechanism of the transient flow field has not been studied yet.…”

A fully coupled analysis of unsteady aerodynamics impact on vehicle dynamics during braking

“…These two types of analyses are sometimes combined to solve the FSI problem. Cheng et al (2013) in their research studied car body aerodynamic damping during pitching. To do that, they selected the transient numerical simulation based on the LES method and the vehicle motion was realized with the arbitrary Lagrangian-Eulerian (ALE) method.…”