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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.

The new Bora, released to the China market in June 2018, is entirely upgraded compared to the previous generation. In the phase of aerodynamic development, CFD was extensively used to improve the new Bora’s design, especially in the early stage of development. During the styling stage, some key aerodynamic features were incorporated into the new Bora design which considerably reduced the aerodynamic drag. The design of the new cooling module seal and the underbody panels also greatly improved the aerodynamic performance. These in total have resulted in 11% drag reduction of the new Bora, over its previous generation. The performance improvement was confirmed in the wind tunnel test and the comparison between wind tunnel test results and CFD results was very good.

The recent facelift of the Chinese version of the VW Bora incorporated several changes of the styling of the upper body. In particular, front facia, A-Pillar and rear end were subject to design changes. As major effects on the aerodynamics performance were not expected, extensive wind tunnel testing for the upper body design changes was not included in the development plan except for final performance evaluation. Nevertheless, an aerodynamic study of the effects of the design changes was undertaken using a CFD based process. At the same time, the facelift offered the opportunity for reducing the aerodynamic drag by improving the underbody flow. The design of the engine undercover and the wheel spoilers were considered in this effort. For this purpose the CFD based aerodynamic study was extended to include respective design features.

Owing to the advantages and the rapid development of CFD methods in recent decades, CFD has become one of the most widely used tools in the field of automotive aerodynamic development. To improve the credibility of simulation, benchmarking with experiment is necessary, for which a large variety of factors should be considered, including the accuracy of digital model for the vehicle, the replication of the experimental environment in the simulation, and others. In the current aerodynamic development of passenger cars at FAW-VW, CFD models used for evaluation and optimization of aerodynamic performance replicate an open-road scenario with low blockage and full moving floor. In order to improve the benchmarking accuracy, the study of the influence of the wind tunnel geometry and ground system on simulation was carried out in this paper.