Abstract:
Increases in the price of petroleum fuels have significantly
affected the importance of aerodynamic drag on commercial vehicle
operating costs. The considerable savings to be made have resulted
in: (i) the appearance of numerous 'add-on' devices intended to
reduce the drag-of existing vehicles, and (ii) an acceptance by
vehicle manufecturers of the importance of aerodynamics to their
new designs. The majority of drag optimisation programmes are
carried out using scale models in a wind tunnel, and the effectiveness
of resulting modifications is often confined to the individual vehicle
concerned. The relatively crude simulation techniques have been
acceptable on the basis that potential errors are small compared to
the reductions in drag that can be achieved. If the trend in
reducing drag is to be maintained a greater understanding of the flow
around commercial vehicle configurations will be needed, especially
under simuleted,crosswind conditions, together with improvements to
the wind tunnel techniques used to simulate the full scale environmen
The experimental programme presented in this report is intended to
Illustrate ,the influence of wind tunnel simulation technique, on the
methods for reducing commercial vehicle aerodynamic-drag.
result in wind tunnel tests over a 'range of simulated
crosswind conditions and levels of free stream turbulence are present
illustrate the significance of variations in Reynolds number,
vehicle geometry, and wind tunnel size on the pressure distribution 2.
and resulting diagonal forces on the vehicle. I.Jrfece pressure contours
are ceteidgued.t0 give insight into the flowfield, around the vehicle
in
relation to the problems of body fouling and water spray
generation although analysis here specifically concerns aerodynamic
drag. Techniques for reducing drag relate primarily to modifications
Of the forebody flowfield and results from a number of experimental
Programmes are collated to illustrate the effectiveness of various,,,
techniques on different vehicle geometries.
