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Vehicle aerodynamic development is normally undertaken in smooth flow wind tunnels. In contrast, the on-road environment is turbulent, with variations in the relative velocity experienced by the moving vehicle caused mainly by the effects of atmospheric turbulence. In this review the turbulence inherent in the atmosphere is considered, following the approach of wind engineers. The variations of atmospheric wind velocity with time, height, terrain and thermal stratification are summarised and discussed. Statistical parameters presented include mean velocity, turbulence intensities, spectra and probability density functions. The resulting fluctuating approach flow (relative velocity) of the moving vehicle is then considered. The effect of the fluctuating velocity field on parameters of interest to vehicle aerodynamicists (such as aerodynamic noise) are made.

Future generation road networks are intended to feature improved throughput and significantly reduced fleet energy consumption. ‘Platooning’ arranges moving vehicles in close longitudinal convoy, and is viewed as a core aspect of such technologies. The aerodynamic performance of platoons potentially allows increased traffic throughput and a useful energy reduction; however the magnitude of this reduction varies significantly with inter-vehicle spacing. For some vehicles in platoons under specific conditions, the resulting aerodynamic performance may actually worsen [2]. This work attempts to deconstruct relationships between two key vehicle geometries and their aerodynamic performance in platoons. A study of homogeneous and heterogeneous platoons using common reference models is presented.

Separated flow is the main generator of aerodynamic noise in passenger vehicles. The flow around the A-pillar is central to the wind noise as many modern vehicles still have high fluctuating pressures due to flow separations in this region. Current production vehicle geometry is restricted due to the amount of three dimensionality possible in laminated windscreen glass (and door opening etc). New materials (e.g., polycarbonate) offer the possibility of more streamlined shapes which allow less or no flow separation. Therefore, a series of experimental investigations have been conducted to study the effects of the A-pillar and windshield geometry and yaw angles on the local flow and noise using a group of idealised road vehicle models. Surface mean and fluctuating pressures were measured on the side window in the A-pillar regions of all models at different Reynolds numbers and yaw angles.

Green racing technologies are described with a focus on two categories of sustainable racing; solar racing, including an overview of the World Solar Challenge (WSC) held in Australia, and Formula SAE-E (Society of Automotive Engineers-Electric). Both types of cars utilise sustainably generated electricity, the former uses solar arrays integrated into the vehicle body and the latter electricity generated from a renewable energy park and stored onboard in lithium polymer cells. The design considerations of both vehicles are contrasted with a focus on energy usage minimisation. The Aurora team (which has broken many records, including winning the World Solar Challenge across Australia) is used to illustrate the importance of minimizing the power requirements by having a low aerodynamic drag, frontal area, a highly efficient powertrain and low rolling resistance. To illustrate the technology behind FSAE Electric the R10E car from RMIT is described.

Effective rear view vision from external mirrors is compromised at high speed due to rotational vibration of the mirror glass. Possible causes of the mirror vibration are reviewed, including road inputs from the vehicle body and a variety of aerodynamic inputs. The latter included vibrations of the entire vehicle body, vibrations of the mirror “shell”, the turbulent flow field due to the A-pillar vortex (and to a lesser extent the approach flow) and base pressure fluctuations. Experiments are described that attempt to understand the relative influence of the causes of vibration, including road and tunnel tests with mirrors instrumented with micro accelerometers. At low frequencies, road inputs predominate, but some occur at such low frequencies that the human eye can track the moving image. At frequencies above about 20Hz the results indicate that at high speeds aerodynamics play a dominant role.

Future Generation Intelligent Transport Systems (FGITS) will likely implement solutions to increase traffic density and thus throughput on existing infrastructures. Platooning (e.g. the close coupling of vehicles) may be a prominent feature of this solution, placing an understanding of near wake flows paramount to the FGITS case. However the notion of vehicles spaced at greater intervals is not only more commonly associated with present day conditions; it is furthermore characteristic of mixed-fleet conditions. These are likely to span the significant era between present day and complete FGITS fleets. Thus, far wake flows are similarly relevant. Near and far wake analysis of a variable geometry Ahmed Model (a research form able to replicate structured wakes pertinent to practical vehicle flows) is used to explore relevant generic flow structures.

This paper is the first of two papers that address the simulation and effects of turbulence on surface vehicle aerodynamics. This, the first paper, focuses on the characteristics of the turbulent flow field encountered by a road vehicle. The natural wind environment is usually unsteady but is almost universally replaced by a smooth flow in both wind tunnel and computational domains. In this paper, the characteristics of turbulence in the relative-velocity co-ordinate system of a moving ground vehicle are reviewed, drawing on work from Wind Engineering experience. Data are provided on typical turbulence levels, probability density functions and velocity spectra to which vehicles are exposed. The focus is on atmospheric turbulence, however the transient flow field from the wakes of other road vehicles and roadside objects are also considered.

Wind tunnels provide a convenient, repeatable method of assessing vehicle engine cooling, yet important draw-backs are the lack of a moving ground and rotating wheels, blockage constraints and, in some tunnels, the inability to simulate ambient temperatures. A series of on-road and wind-tunnel experiments has been conducted to validate a process for evaluating vehicle cooling system performance in a high blockage aerodynamic wind tunnel with a fixed ground simulation. Airflow through the vehicle front air intake was measured via a series of pressure taps and the wind-tunnel velocity was adjusted to match the corresponding pressures found during the road tests. In order to cope with the inability to simulate ambient temperatures, the technique of Specific Dissipation (SD) was used (which has previously been shown to overcome this problem).

A KIA Soul was instrumented to measure the relative velocity (magnitude and yaw angle) at the front of the vehicle and in-cabin sound at a location close to the side glass near the A-pillar vortex impingement. Tests were conducted at a proving ground under a range of conditions from low wind conditions (~3 m/s) to moderate (7-8 m/s) wind speeds. For any given set of atmospheric conditions the velocity and sound data at any given position on the proving ground were noted to be very repeatable, indicating that the local wakes dominated the "turbulent" velocity field. Testing was also conducted in an aeroacoustic wind tunnel in smooth flow and with a number of novel turbulence generating methods. The resulting sounds were analyzed to study the modulation at frequencies likely to result in fluctuation strength type noise.