On-road and wind tunnel turbulence and its measurement using a four-hole dynamic probe ahead of several cars

On-road measurements combined with a review of the literature suggest that it is rare for cars to travel in turbulence intensities less than 1%. It is typically 3%-5%. In an open, unobstructed environment, the length scale ranges from 2-17 m (average = 7 m). Alternatively, the presence of upstream motor cars reduce the length scales to 0.5-1.5 m (average = 1.2 m), but the cars increase the turbulence intensity from 5% to 20%. The placement of a similar size car one body length upstream in a wind tunnel presents an environment for aero-acoustic noise testing and perhaps other aerodynamic testing that is more typical of average freeway conditions than is normally found in most wind tunnels.