On-road pressure measurements on a full scale heavy-duty truck

An experimental study of the pressure distribution at the rear of a full tractor–trailer vehicle is presented. The influence of the underbody flow blockage is investigated. The measurements are performed using a differential pressure sensor. Stability of reference pressure during tests is required, and its knowledge allows to sort measurements in terms of reliability. A device is designed to measure the reference pressure and a corrective term allows it to be related to the atmospheric pressure in rolling conditions. The estimated repeatability of the measurements is around 1% for a reference underbody configuration. For various opening ratio of the underbody, changes in the overall pressure force on the rear surface, denoted by the product S 〈 C p ¯ 〉 between the area of the rear surface S and the spatial average of the pressure coefficient 〈 C p ¯ 〉 , are mostly driven by the changes in rear surface. Finally, configurations with constant free spaces whose position are varying were considered. In this case, the vertical position of the free space is of primary importance for S 〈 C p ¯ 〉 , with relative variations up to 18% between the lower and upper positions of the ground clearance free space.