Abstract
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
o Simulation (CFD)
o Wind Tunnel
o 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.
Keywords: Aerodynamics, CFD, Simulation, Wind Tunnel, Road Test