Numerical quantification of aerodynamic damping on pitching of vehicle-inspired bluff body

Abstract

The influence of transient flows on vehicle stability was investigated by large eddy simulation. To consider the dynamic response of a vehicle to real-life transient aerodynamics, a dimensionless parameter that quantifies the amount of aerodynamic damping for vehicle subjects to pitching oscillation is proposed. Two vehicle models with different stability characteristics were created to verify the parameter. For idealized notchback models, underbody has the highest contribution to the total aerodynamic damping, which was up to 69%. However, the difference between the aerodynamic damping of models with distinct A-and C-pillar configurations mainly depends on the trunk-deck contribution. Comparison between dynamically obtained phase-averaged pitching moment with quasisteady values shows totally different aerodynamic behaviors.

Aerodynamic stability of road vehicles in dynamic pitching motion

“…Cheng et al (2011) reported that the aerodynamic effect due to the trailing vortices shed from the front pillar (which correspond to the A-pillar in the case of sedan-type passenger car) tended to destabilize the model's pitching oscillation, while the aerodynamic effect due to the trailing vortices shed from the rear pillar (which correspond to the C-pillar) tended to stabilize it. Hence, the model with rounded front pillar and angular rear pillar exhibited a significantly higher aerodynamic damping than the model with the opposite pillar shape configurations (Cheng et al, 2012).…”

“…To overcome these limitations, therefore, we have developed in the earlier phase of the study a numerical method which can resolve the spatial and temporal details of the flow properties, for the assessment of vehicle aerodynamic stability performance in a transient driving situation (interested reader is referred to Nakashima et al (2009) and Cheng et al (2011, 2012). In regard to the aerodynamic stability performance of vehicles, most studies reported in the literature were focus on yawing.…”

“…The flow structures generated by these body parts can interfere between one another and render the results of investigation inconclusive. To overcome this problem, we simplified the vehicle shape by employing the models with simple bluff body shape in the earlier phase of the study (Nakashima et al, 2009;Cheng et al, 2011Cheng et al, , 2012. This enables the isolation of the subject of investigation, i.e.…”

“…In these investigations (Nakashima et al, 2009;Cheng et al, 2011Cheng et al, , 2012, a coupling of ALE (Hirt et al, 1974) and LES methods had been employed to realize the vehicle body motion during fluid flow simulations, and to obtain the time-resolved results. As such, the studies were able to probe the dynamic response of the vehicle due to pitching oscillation.…”

Influence of rear-roof spoiler on the aerodynamic performance of hatchback vehicle

“…Hence, it helps to provide insight into how each spoiler configurations would perform under a more realistic driving condition if certain motion mode could be incorporated in the flow simulation. For this purpose, the method introduced by Cheng et al [10,11] could be employed in the future studies.…”