Detached eddy simulation of a closely running lorry platoon

Abstract

In recent years, the concept of autonomous road vehicles has gained a great deal of technical respectability, with expected fuel benefits arising from running vehicles closely in platoons. However, the aerodynamics of such vehicles travelling in close proximity is still not understood. This paper presents for the first time a detailed study of drag benefits and the flow structure around a platoon of high-sided lorries, through conducting Delayed Detached Eddy Simulations (DDES). The lorry surface pressure and slipstream flow characteristics show good agreement with experimental data. Drag reductions of up to 70% have been observed for all trailing lorries in the platoon. Analysis of the flow field indicated highly turbulent regions on the top and sides of trailing lorries. Turbulent kinetic energy and Reynolds stresses were found to concentrate at the connection region between lorry cab and box. Spectral analysis of the side forces identified oscillating behaviour on each lorry in the platoon due to strong vortex shedding, suggesting that platooning lorries are potentially more likely to develop lateral instabilities than an isolated lorry. The study indicates that autonomous vehicle developers and operators should consider the significant drag reduction benefits of platooning against the risk associated with potential lateral instabilities.

Unsteady aerodynamic forces on long lorry platoons

“…The drag decreased with spacing, with a 57% reduction for the closest spacing. Drag results for the same platoon configuration, obtained via Delayed Detached Eddy Simulation (DDES), were in excellent agreement with the experimental results (He et al, 2019). This reduction in aerodynamic drag is perhaps the major advantage of platooning given the increasing demand for more environmentally friendly transport systems and global needs for decarbonisation.…”

“…Similarly, the simulations by Humphreys and Bevly (2016) showed that the trailing vehicle in a two-truck platoon experienced buffeting, presumably due to vortices shed by the front vehicle. The DDES results on the eight-lorry platoon mentioned above (He et al, 2019) suggested that lorries in platoons could experience significant oscillating lateral forces, which increased along the platoon. This paper considers this issue and in particular looks at unsteady lateral forces on lorries in platoons, and the unsteady nature of the flow field around them, using the experimental data from the investigations of Robertson et al (2019) and, to a limited extent, the computational data of He et al (2019) described above.…”

“…There has been some recent work to investigate the aerodynamics of platoons including fullscale field tests (CORDIS, 2012;Chan, 2012;Davila et al, 2013;Ebrahim, 2018), scale-model laboratory testing (Zabat et al, 1995;Tsuei & Savaş, 2001;Robertson et al, 2019;Le Good et al, 2018;Watkins and Vino, 2008;Pagliarella et al, 2007) and Computational Fluid Dynamics (CFD) (Davila et al, 2013;He, et al, 2019;Vegendla et al, 2015;Humphreys and Bevly, 2016;Mirzaei and Krajnović, 2016;Bruneau et al, 2017;Ebrahim and Dominy, 2020). This work has also focused on changes to the mean drag force of vehicles in platoons.…”

Wake and surface pressure analysis of vehicles in platoon

“…In general, platoon aerodynamics are difficult to test in wind tunnels due to the limited test section length required to accommodate a large number of vehicles without compromising the vehicles scale, which in turn influences the aerodynamic resolution and Reynolds number. CFD therefore offers a practical alternative to assess vehicles in platoon as demonstrated by several authors using RANS (Jacuzzi and Granlund, 2019) DDES (He et al, 2019) and DNS (Bruneau, Khadra, and Mortazavi, 2017). Both He et al and Bruneau, Khadra, and Mortazavi demonstrated the advantages of using higher order numerical solvers to determine time dependant flow features in platoon that are usually omitted by RANS that contribute to the vehicle's lateral instability.…”

Numerical Simulation and Analysis of Aerodynamic Characteristics of Road Vehicles in Platoon

“…The results indicated that the overall fuel economy of two truck platoon was improved as the separate distance decreased [5]. The aerodynamic characteristics and stability of the lorries platoon were investigated with delayed detached eddy simulations (DDES) and experiments [6]. Findings demonstrated that up to 60% reduction in drag was achieved for the intermediate trailing lorries.…”