The Decay of Bluff Body Wakes 2011-01-0178

Vehicles on the road operate in the turbulent flow field resulting from the combined effects of the natural wind and the wakes of other vehicles. While substantial data exists on the properties of the natural wind, much less information is available for the wake properties of road vehicles. The wake information available for road vehicle shapes is mainly restricted to the near wake region, but to understand the vehicle operating environment it is the wake downstream of this region which is of interest. To determine the range of this area of interest requires some knowledge of the decay of the wake properties. From wind tunnel studies using small simple bluff bodies in free stream and in ground proximity the principle wake properties, velocity deficit and peak turbulence intensity have been measured. The maximum velocity deficit is shown to approximately decay with x^-2/3, where x is the distance downstream, while turbulence intensity decays at a slightly slower rate. A relationship with body drag is established. Ground proximity is shown to significantly modify the velocity distribution in the wake.