Wind-tunnel tests were conducted using a 30%-scale DrivAer model, in estateback
and notchback rear-geometry configurations, to investigate aerodynamic
performance changes associated with snow and ice buildup on passenger vehicles.
Around 20 snow/ice accumulation patterns were tested, at a Reynolds number of
2.8 × 106 based on model wheelbase, for each of
the notchback and estateback variants. 5 additional patterns were tested on the
estateback with roof-rack support bars. Snow accumulation was modelled with
foam, while ice accumulation was simulated with aluminum tape hand-formed to the
desired shape. A simulated full-scale snow thickness of 58 mm on the hood, roof
and trunk increased the wind-averaged drag coefficient by 16% for both model
variants. With 90 mm of snow, the drag of the estateback variant increased by
19%. Drag changes increased with, but were not proportional to, snow thickness.
Chamfered front and rear edges, representing windblown shapes, reduced the drag
penalty compared to square-edged snow models. The largest drag increases, of 18%
and 20%, respectively, for the notchback and estateback configurations, were due
to simulated patchy snow and ice on multiple surfaces. Localized ice/snow
patches sometimes caused stronger increases in drag than a similar or larger
volume of precipitation elsewhere. Critical surfaces include the A and aft-most
(C/D) pillars, the lower-front corners, the leading-edge of the hood and the
leading- and trailing-edges of the roof. Simulated snow and ice at more upstream
positions often caused higher increases in drag than accumulations further
downstream. Drag and base pressure were more likely to be correlated for changes
closer to the rear of the model. Some snow/ice patterns were found to increase
side force and rolling moment in crosswinds, or to increase lift and change the
pitching moment, potentially affecting vehicle stability and traction. The
results are intended to support additional studies that will examine the impacts
of snow/ice accumulation on fuel/energy use and safety.