Aerodynamic drag reduction by means of platooning configurations of light commercial vehicles: A flow field analysis

Abstract

Platooning configurations of two, three and four commercial vehicles were tested at a Reynolds number based on the vehicle’s length (L) of230000. The platoon configurations were obtained using an instrumented model, and three wooden replicas located at different positions with respect to the instrumented one. The reference model presents a slant angle at the leading edge, which can produce, in principle, a significantly different flow field compared to the generally studied Ahmed body. Drag, static pressure distributions and pressure fluctuations measurements were carried out. Additionally, planar PIV measurements were performed to investigate the near wake of the two-vehicles platoon configuration.For the two-models platoon, drag reductions of 30% and 43% were evidenced for the front and for the rear vehicle, respectively, at an inter-vehicle distance (d) equal to half the vehicle’s length, and corresponding to an average drag reduction of 36.5%. For increasing distance, the benefit associated with the platooning configuration reduces, reaching an average drag reduction of 20% atd/L = 3. We relate the vehicle’s drag to the flow field organization and to the distribution of the modal energy through Proper Orthogonal Decomposition of the microphonic probes located on the base of the instrumented vehicle. We also evidence that the key element that is responsible for the pumping of the wake is the large vortex that generates near the top edge of the vehicle’s base.We show that the slant angle does not affect the drag reduction of the leading vehicle of the platoon, whereas it can lead to larger differences in the case of the rear vehicle.For three and four-vehicles platoons, consistently larger values of the average drag reduction are experienced (≈35%) and were also obtained for distances >1L. A simple model describing the overall drag reduction for a generic number of vehicles is presented and discussed.