Abstract
The results of the perennial cooperative research work between the BMW Group and the
Research Institute of Automotive Engineering and Vehicle Engines Stuttgart (FKFS) are
presented here. In recent years, several methods of reducing fuel consumption have been
explored. These include aerodynamic shape optimization and other potential methods such as
a smooth underbody.
However, as the power of engines increases, more effective cooling is needed, resulting in
increased cooling air mass flow requirements. This increase in airflow in turn requires an
increase in size of the air inlets, usually resulting in an increase in the vehicles aerodynamic
drag and hence a conflict of interests. To resolve this issue the potentials of aerodynamic
design have to be researched.
In addition to the above issue, it is known that the missing interference phenomena of models
without internal flow cause the model to exhibit different characteristics than a full scale
production vehicle. Therefore it is important to realize the interaction between external and
internal flow.
If the implementation of cooling airflow in the models is supplemented by measurements to
determine the cooling air mass flow, a variety of new perspectives for the aerodynamic
development process is opened up. Body shape configurations can consequently be analyzed
with respect to their influence on cooling airflow.
The volume flow rate through the radiator in full size models is measured with a hot-wire
radiator traverse, which is well-known for its high resolution of the airflow speeds. Due to the
used hot-wire probes, unfortunately it is not possible, to carry out warm vehicle testing with
the same measurement system. To be able to measure during driving, the system was replaced
by a temperature resistant technique.
Because it is not possible to minimize the size of the traverse, it was also necessary to develop
a new measurement system especially for all kinds of vehicle studies.
Compared among each other, every technique shows a sufficient precision and a high
repeatability according to the required results.
Using these three measurement technologies, the complete development process chain is
covered with respect to cooling airflow measurements. Scaled models, full sized models as
well as production cars can be investigated. Furthermore the compatibility of the individual
results along the chain has been proven.
In the second part of the presentation, the potential of body shape modifications, in other
words, proportion parameter modifications, on internal airflow are analysed. It is to be shown
that modifications even in areas that would normally not be expected to cause large effects on
the internal airflow, can generate a considerable influence on the mass flow.
The cooling airflow measuring techniques, the transferability of the measurements on models
to the production vehicle and the influence of several body shell parameters on cooling
airflow will be demonstrated during the presentation.
Keywords - Aerodynamic, process, design, development, cooling-measurement.