Effects of Vehicle Numbers and Vehicle Types on Drag Reduction of Platoons with Different Front-Edge Radius 2023-01-0951

The platoon of intelligent vehicles can significantly reduce the aerodynamic drag, which has broad development prospects. This research numerically studies the effect of Reynolds number (Re = 3.32×10⁵ to 19.94×10⁵), the vehicle numbers (3-, 5-, 8-vehicle), and vehicle types (fastback, notchback, and squareback) on the platoon drag reduction with three different front-edge radius (R^*=R/W×100 = 9.36, 4.68 and 2.34). The results show that when the Reynolds number is greater than 9.97×10⁵, the drag coefficient ratio C_D/C_Di (C_Di is the drag coefficient of the isolated vehicle) of each vehicle in the platoon is less affected by the Reynolds number. When R^*=9.36, the averaged C_D/C_Di of the fastback platoon (even above 1) is higher than that of both the notchback platoon and the squareback platoon without front-edge separation at the leading vehicle due to the weakest shielding effect on the following car resulting from the prominent downwash wake. Compared with R^*=9.36, when the flow separation occurs at the front-edge R^*=2.34, the averaged C_D/C_Di of the platoon with different vehicle numbers and each vehicle (except the leading vehicle) in the platoon both exhibit a tremendous reduction. This drag reduction should be attributed to the shielding effect caused by the front-edge separation at the leading vehicle. In addition, at the front-edge R^*=2.34, the averaged C_D/C_Di of the fastback and squareback platoon are comparable, much larger than that of the notchback platoon featured by a balanced wake and shortened recirculation flow at in-notch region. Except for the fastback platoon at R^*=9.36, the other platoon's averaged C_D/C_Di decreases gradually with the increase of vehicle number. This work has a vital reference significance for the aerodynamic optimization design of the future intelligent vehicle platoon.