Aerodynamic Effects of Roof Deflector and Cab Side Extenders for Truck-Trailer Combinations 2011-01-2284
Today there are a large variety of drag-reducing devices for
heavy trucks that are commonly used, for example, roof deflectors,
cab side extenders and chassis fairings. These devices are often
proven to be efficient, reducing the total aerodynamic resistance
for the vehicle. However, the drag-reducing devices are usually
identical for a specific pulling vehicle, independent of the layout
of the vehicle combination.
In this study, three vehicle combinations were analyzed. The
total length of the vehicles varied between 10.10 m and 25.25 m.
The combinations consisted of a rigid truck in combination with one
or two cargo units. The size of the gap between the cargo units
differed between the vehicle combinations. There were also three
configurations of each vehicle combination with different
combinations of roof deflector and cab side extenders, yielding a
total number of nine configurations.
The aim of this investigation was to determine the aerodynamic
effects of the roof deflector and cab side extenders as a function
of the type of vehicle combination. Important factors were the
total length of the vehicle combination and the influence of the
drag reducing devices further downstream. The investigation was
performed using Computational Fluid Dynamics (CFD).
The results from the investigation showed that the effect of the
two drag-reducing devices analyzed was different depending on the
type of vehicle combination. It was established that the roof
deflector and cab side extenders were always efficient in reducing
drag both in 0° yaw and 5° yaw but the magnitudes differed between
the configurations. The largest effects of the drag-reducing
devices were seen for the truck including the 1st cargo unit; the
influence of the drag-reducing devices on the 2nd cargo unit was
smaller. The aerodynamic reductions were diminishing downstream,
why it was concluded that it is of great importance to improve the
aerodynamic design of the rest of the vehicle to maintain the
positive effects of the drag reducing devices.