The mutual aerodynamic influence of road vehicles in close proximity is known to
alter significantly the drag performance of the vehicles. This paper presents an
extended analysis from a study of two open-access road-vehicle shapes (a DrivAer
Notchback model and an AeroSUV Estateback model) in close lateral proximity with
each other, or with other vehicle shapes. Wind-tunnel measurements were
conducted for a yaw-angle range of ±10°, for lateral distances representing 75%,
100%, and 125% of a typical highway lane spacing, and for longitudinal distances
up to 2 vehicle lengths forward and back. The results of a previous analysis of
the data, which examined aerodynamic force measurements only, showed changes in
drag coefficient of ±20% or more depending on the relative locations and wind
conditions. In this paper, the force-coefficient results reexamined, and
surface-pressure measurements are introduced to investigate the sources of the
performance changes.
The results suggest that the changes in aerodynamic performance of vehicles in
close lateral proximity arise from three mechanisms: 1) from a combination of
locally-reduced static pressure, due to the combined blockage effect of the two
vehicles on the local flow field; 2) from local flow-angularity changes altering
the effective yaw angle of each vehicle; and 3) from wake-body interactions. The
results also demonstrate a small increase in proximity effect when a proximate
Ahmed body is introduced instead, likely as a results of its larger internal
volume, but with trends that match the DrivAer/AeroSUV results.
Proximity-induced loads and pressures are shown to increase with reduced
distance and with increased adjacent-body size.