Wake and surface pressure analysis of vehicles in platoon

In this paper, the drag reduction benefits associated with 2 and 3 cars in platoon have been investigated. Following a validation of initial CFD simulations against experimental measurements, predictions of surface pressures and wake structure for alternative platoon configurations have been analysed to determine the changes of flow structure that influence the pressure field and drag force on each vehicle. Contrary to several publications it was found that in a platoon of two vehicles, the drag force of the trailing vehicle exceeded that of an isolated vehicle for close spacings. Analysis of this surprising result revealed that design features introduced to optimise the wake of an isolated vehicle can lead to a drag increase on a following vehicle. For three-vehicle platoons, the flow interaction between the leading and middle vehicles remained largely unchanged but the additional effect of the third vehicle resulted in all three vehicles exhibiting lower drag than that of an isolated vehicle. A clear implication of this work is that results from the analysis of vehicle platoons are likely to be sensitive to the geometry and wake structures of the chosen test vehicle which helps to explain why many previous studies have been seemingly contradictory.