Terrestrial winds play an important role in affecting the aerodynamics of road vehicles. Of increasing importance is the effect of the unsteady turbulence structure of these winds and their influence on the process of optimizing aerodynamic performance to reduce fuel consumption. In an effort to predict better the aerodynamic performance of heavy-duty vehicles and various drag reduction technologies, a study was undertaken to measure the turbulent wind characteristics experienced by heavy-duty vehicles on the road.
To measure the winds experienced on the road, a sport utility vehicle (SUV) was outfitted with an array of four fast-response pressure probes that could be arranged in vertical or horizontal rake configurations that provided measurements up to 4.0 m from the ground and spanning a width of 2.4 m. To characterize the influence of the proximity of the vehicle on the pressure signals of the probes, the SUV and its measurements system was calibrated in a large wind tunnel. On-road measurements of the turbulence intensities, turbulence length scales, wind spectra, and spatial correlations were performed. Eight days of testing over a two month period in late 2012 were conducted over roads in Eastern Ontario and Western Quebec, Canada. Dates and test routes were selected to provide a variety of conditions. The time-series of on-road turbulence data were segmented and classified based on differences in the terrain roughness, traffic density, and wind strength experienced during the measurements.
Of the three classification categories, traffic density provided the greatest influence on the measured turbulence characteristics by modifying the strength of the high-frequency/small-scale turbulence structures in the wind. Conversely, the strength of the terrestrial winds provided a strong influence on the low-frequency/large-scale turbulence. In the near-ground region of the current study (0.5 to 4.0 m), which represents the vertical extent of typical heavy duty vehicles on the road, the turbulence length scales showed a much greater sensitivity to vertical distance than did the turbulence intensity, resulting from damping of the large-scale/low-frequency wind fluctuations near the ground.
Based on the frequency of the various conditions experienced on the road, a target set of wind conditions, (intensities, length scales, spectra, correlation lengths) are recommended that differ from previously-published recommendations.
