Abstract
Reduction in aerodynamic drag is essential in the vehicle design in the environmental
protection emphasized society. The computational fluid dynamics (CFD) is being
acknowledged as an inevitable tool in the modern vehicle aerodynamic design. Vehicle aero-dynamicists continue to investigate to what extent advanced CFD can really reproduce physical
phenomena of the flow around the vehicle. How to effectively use CFD techniques in the
daily aerodynamic design process is major concern for shorter lead-time of vehicle design.
Objectives of this paper are to review previous studies on aerodynamic underbody designs in
terms of both experimental aspects and CFD and also to show the authors´ several new com-putations toward a successful low Cd design of the underbody.
Three turbulence models, i.e., k- model, Reynolds stress model (RSM) and large eddy simulation
(LES), are compared with the experimental data in terms of pressure distribution of
ASMO body using the CFD code "FrontFlow-red". Effects of semi-complex underbody configurations
on Cd of the vehicle body are examined in terms of optimized underbody configuration
design and also an alternative of flat configuration for better estimation of Cd in the
early design stage. Underbody configurations investigated are exhaust pipe area (center cavity),
rear suspension area (rear cavity) and wheel housing. Effects of k- model and RSM are
also compared.
This paper also mentions the importance of the wheel rotation during the aerodynamic development,
which is nowadays acknowledged in the aerodynamic community. There are many
possible ways to model wheel rotation within CFD techniques. A comparison on the most
common two methods, i.e., applying surface velocity condition and use of multiple rotating
reference frame (MRF), based on the FKFS results achieved with EXA PowerFLOW TM on a
single rotating wheel, shows the advantages, drawbacks and resulting quality of these methods.
Keywords - Underbody Design, Wheel Rotation, CFD, RANS, LES