The aerodynamics of close running ground vehicles

In recent years the concept of driverless or autonomous road vehicles (AVs) has gained a great deal of technical respectability and most major manufacturers intend to bring a partially or fully autonomous vehicle to market within the next few years. Much progress has been made on a range of technologies relevant to this concept, including digital mapping, position recognition by lidar and radar systems and advanced vehicle to vehicle communications. There are a number of advantages for such vehicles over normal driver controlled vehicles in terms of safety, reliability, access for the disabled and increasing the efficiency of road use. The latter comes about primarily because such vehicles are able to drive closely together in platoon formation. This project is concerned with a technical area associated with platoon running. where to date only a restricted amount of experimental work has been carried out - that of the aerodynamics of vehicles travelling in platoons, and the nature of the flow field in and around platoons is not well understood. In particular the following aspects will be investigated.
a) The overall stability of vehicles travelling in the wake of other vehicles, particularly if there are organised coherent wake flow structures such as trailing vortices. These stability effects may be made more severe by the presence of slight cross winds that result in asymmetric and variable wakes, which can be expected to occur for the majority of the time.
b) Problems associated with exhaust pollutants can also be envisaged, as it is possible that pollutants may build up along the length of the platoon and not be released into the open atmosphere, and may, if the conditions are suitable, be ingested by vehicle power plant and ventilation systems.
c) Aerodynamic noise is an important design consideration for road vehicles, both in terms of passenger and driver comfort, and in terms of the overall effect of traffic on the surrounding environment. It is not clear how the use of platoon running of AVs will affect the internal and external propagation of aerodynamic vehicle noise.
In addition work is proposed to investigate a related problem - the aerodynamic aspects of trains running very closely together, an issue which has emerged from recent studies of high speed coupling and uncoupling operations.
This work will be carried out through physical and computational modelling. The physical modelling work will utilise the University of Birmingham moving model TRAIN Rig, which allows individual and platoons of vehicles to be propelled along a 150m long test track at speeds of up to 80m/s. The work will involve detailed measurements of pressure over the vehicles (such that aerodynamic forces can be calculated), and measurements of aerodynamic noise propagation from platoons and pollutant dispersion from platoons. The computational work will be carried out using conventional RANS techniques for a wide range of vehicle and platoon configurations, but also a smaller number of calculations using more sophisticated DES and LED methods to provide high quality unsteady flow information. Taken together, the physical modelling results and the CFD will enable a detailed understanding to be achieved of the aerodynamic behaviour of ground vehicles running closely together, which will be of considerable interest and importance to a variety of stakeholders.

The major impact of the research for stakeholders will be as follows.
a) Manufacturers of autonomous vehicles - detailed information on drag, lift and vehicle stability for a range of vehicle types and spacings, information on pollution dispersion and noise levels within the different platoons.
b) Operators of transport systems using autonomous vehicles - guidance for design of AV control systems, information on the spread of noise and pollutants away from vehicle platoons.
c) Train operators interested in close running of vehicles - information on aerodynamic instability effects for trains running in close formation.
These benefits will be achieved through direct dissemination to key stakeholders who are project partners and serve on the project Steering Committee; through strong interaction with the Transport systems Catapult Centre - the UK transport innovation centre based in Milton Keynes; through dissemination seminars and a major final London based event; and through publication in academic and professional journals.