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Automotive manufacturers are under continuous pressure to satisfy changing consumer demands and regulatory requirements in an increasingly competitive landscape. This requires Aerodynamic departments to evaluate more design ideas in less development time. Aerodynamic departments are seeking to speed up their analysis in order to provide more feedback on performance to design and styling. Vehicle designers already leverage Computational Fluid Dynamics in order to quickly assess vehicle aerodynamic performance during product development. However, in order to meet modern development challenges, reducing simulation cost and turn-around-time is necessary. To that end, a novel approach to reducing simulation time of vehicle aerodynamics without sacrificing accuracy was tested in this paper. The methodology is called Transient Boundary Seeding, and enables the usage of a reduced simulation domain without the loss of information from the omitted region.

Government regulations and consumer needs are driving automotive manufacturers to reduce vehicle energy consumption. However, this forms part of a complex landscape of regulation and customer needs. For instance, when reducing aerodynamic drag or vehicle weight for efficiency other important factors must be taken into account. This is seen in vehicle bonnet design. The bonnet is a large unsupported structure that is exposed to very high and often fluctuating aerodynamic loads, due to travelling in the wake of other vehicles. When travelling at high speed and in close proximity to other vehicles this unsteady aerodynamic loading can force the bonnet structure to vibrate, so-called “bonnet flutter”. A bonnet which is stiff enough to not flutter may be either too heavy for efficiency or insufficiently compliant to meet pedestrian safety requirements. On the other hand, a bonnet which flutters may be structurally compromised or undermine customer perceptions of vehicle quality.

The commercial vehicle development process needs to consider the vehicle aerodynamics not only in ideal flow conditions, but also in the turbulent real world environment. The turbulent real world environment includes not only atmospheric turbulence, but also the vehicle to vehicle interactions that happen when driving around other vehicles or into and out of the wake of in/on coming vehicles. A vehicle driving into the wake of an oncoming vehicle not only experiences an increase in the total aerodynamic forces, it also experiences unsteady transient loads over the vehicle components such as windshield, mirror, sunvisor, door and side fairing. To properly design specific components, designers need to understand the magnitude of unsteady forces on various vehicle components, otherwise these components may fail which imposes warranty and safety risks. In this paper, we attempt to understand the various forces acting on the primary vehicle during a passing maneuver.