COMPLEMENTARY USAGE OF SIMULATION, WIND TUNNEL AND ROAD TESTS DURING THE AERODYNAMIC DEVELOPMENT OF A NEW BMW SUV

摘要

In the course of the entire vehicle development process aerodynamics is one of the few disciplines involved from the very early initial phase up to the final serial development. Along this cycle the available data features very different levels of detail. After the kick-off of a new model only generic bodies without underhood and underbody details are provided from styling for the aerodynamic analysis and ranking of different themes. These may be clay models or virtual shapes created with ALIAS. Once the design competition is completed and the exterior skin is frozen, more and more details of the engine compartment and the underbody become available to the aerodynamicist from various other departments. According to the growing maturity of product data also the problems to be addressed are changing. The initial ranking of styling themes with respect to aerodynamic quality is mostly accomplished purely based on drag and lift distribution. However, aerodynamics is closely linked with thermal management and therefore cooling air mass flow rates, performance of the cooling package and component temperatures need to be assessed as soon as the necessary geometry data is available. Another constraint arises from the short time windows in the overall development process in which the aerodynamicist can have an impact on the vehicle. To cope with these tasks the aerodynamicist uses a toolbox consisting of Simulation (CFD) Wind Tunnel Road Test At the BMW group these tools are not considered as competing instruments, rather they are used in a complementary fashion. Each tool has its own advantages and drawbacks and therefore only their clever application to the right problem at the right time delivers a real benefit and aids to shorten cost and time. This paper exemplifies this process in detail on the aerodynamic development of a new BMW SUV to be released in autumn 2006.