Aerodynamics of vehicle platooning
Doctoral thesis, 2023
This thesis focuses on a relatively unutilized way of reducing the aerodynamic drag of vehicles, that is, vehicles driving in close proximity, or platooning. Although such a solution has long been envisioned as a way of reducing drag, it is only now becoming possible with advancements in vehicle automation and communication. Platooning is, however, regularly, and successfully used in many sports.
Although there have been many studies on the topic, the focus has mostly been on the differences in drag. This thesis attempts to improve the understanding of the observed changes in drag for a cab over engine style tractor-trailer, a passenger car, and a coach bus. The work herein was performed using both CFD simulations and wind tunnel experiments. The aerodynamics of platoons were investigated for separation distances between 0.5m and 30m, 0m and 0.5m lateral offsets, and 0°, 5°, and 10° yaw angles, to emulate wind conditions. The effects for different vehicle types are generally similar, although with varying magnitudes depending on the combination.
The results showed that the aerodynamic phenomena of the leading vehicle are, in most cases, fairly straightforward, with a base pressure increase due to the pressure field emanating from the trailing vehicle’s stagnation area. This causes a reduction in drag with a decreased distance and a reduction of the relative savings under yaw conditions. The effects on the trailing vehicle are more complex as they are dominated by changes to the flow field. Many of the changes are generated by the leading vehicle slowing the flow before the trailing vehicle, as well as slight changes to the flow angularity. This typically causes the relative pressure on the front to trend toward zero and the pressure in the tractor-trailer gap to increase. At yaw, similar effects remain, but the trailing vehicle also experiences a decrease in the effective yaw angle, similar to that of a lower yaw angle. The effects on the leading and trailing vehicles generally combine to reduce the drag of the entire platoon as the separation distance decreases. Yawed flow tends to reduce the relative savings for the platoon as a whole, while a lateral offset can recover some of it.
cab over engine
Chalmers, Mechanics and Maritime Sciences (M2), Vehicle Engineering and Autonomous Systems
Törnell, J., Sebben, S., Elofsson, P., Effects of separation distance, lateral offset, and yaw on the drag of a truck and SUV platoon
Reducing the aerodynamic resistance can be done in many ways, most commonly through improving the form of the vehicle, or as was investigated in this work, platooning.
Platooning is when two or more vehicles are driven closely behind each other, which has the effect of reducing their aerodynamic resistance. It is now becoming more feasible to drive at shorter and shorter separation distances as vehicle to vehicle communication and vehicle automation is getting better.
The results of this work shows that although the drag does not always change in the most straight forward way and that the leading vehicle can sometimes see larger benefits than the trailing one. They also show that for trucks, drag van be reduced by as much as 45\% and cars can even experience negative drag, the car is actually pushed forwards by the air. FInally, if very short separation distances can not be achieved, similar improvements can be seen at 10m and 20m.
Aerodynamics of platoons with multiple vehicle types: an optimisation for future transportation systems
Swedish Energy Agency (2017-007896), 2018-01-02 -- 2021-12-31.
Areas of Advance
C3SE (Chalmers Centre for Computational Science and Engineering)
Fluid Mechanics and Acoustics
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5267
Chalmers campus Johanneberg , room HA2, Hörsalsvägen 4
Opponent: Dr. Brian McAuliffe, National Research Council Canada (NRC), Canada