An experimental study on the aerodynamic characteristics of HGVs travelling in close-proximity

With recent advances in connected and autonomous vehicles (CAVs), there is an increasing prospect that it will soon be commonplace for a number of communicating CAVs to travel in close proximity, safely and at high speed, in what is known as a ‘platoon’ formation. Public perception of CAV suggests that early adopters of this technology are likely to be the haulage industry, specifically for heavy goods vehicles (HGVs). This paper presents a series of experiments designed to determine aerodynamic flow structures around a series of HGVs in uniform formation. The experiments were conducted at The University of Birmingham TRansient Aerodynamic INvestigation (TRAIN) rig facility. The platoon consists of either three or five, equally spaced, 1/20th scale lorries, with a Reynolds number of the order of 2.8 × 10 5 . This paper focuses on measurements of the slipstream pressures and velocities around the vehicle. The characteristic slipstream behaviour was shown to be dominated by a series of large-scale flow structures and characterised as a highly turbulent, thick boundary layer development extending laterally and vertically from the vehicle sides. The spacing of vehicles was shown to affect the development of the characteristic flow. Separation from the vehicle front edge rapidly forms into a vortex type structure, emanating from the top corners of the HGV tractor and trailer bodies. Vorticity analysis indicated that suppression of these vortices by the platoon boundary layer flow causes a directional change in rotation in relation the lead HGV. To the side of each lorry trailer there is an ejection of flow from the wheel/underbody region being dragged along in the direction of vehicle motion. Finally, the flow following each lorry has negative vorticity, as it is drawn into the voided space behind the lorry, which then rapidly changes to become positive vorticity, as the following lorry influences the flow of the air back out from this voided space. This effect is repeated along the platoon.