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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.

The function of a rear view mirror is a determining factor in its shape - resulting in a flat rear mirrored face. The resulting bluff body generates unsteady base pressures which generate unsteady forces, leading to movement of the mirror surface and potential image blurring. The objective of this paper was to experimentally determine the fluctuating base pressure on a standard and modified mirror. Half a full-size vehicle was utilised, fixed to the side wall of a wind tunnel. A dynamically responsive multi channel pressure system was used to record the pressures. The modification to the mirror consisted of a series of extensions to the mirror rim, to see if this method would attenuate the fluctuating base pressures. It was found that increasing the length of the extension changed the pressure pattern across the face, and the over all magnitude of the fluctuations reduced with increasing length of extension. It was recommended to further the work via phase measurements.

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.

Noise in passenger cars is dependent upon the fluctuating surface pressures on the exterior, particularly in the region of the A-pillar and the front side glass. The purpose of this work was to investigate whether the fluctuating surface pressure profile obtained in a typical full-size automotive wind tunnel can be duplicated within the limitations of high blockage tunnel. A further aim was to compare the data from both wind tunnels with road data. In order to investigate the spatial resolution of fluctuating pressures on the side window of a car, flush mounted microphones were used as fluctuating pressure transducers. Mean pressure coefficients were obtained from flush-mounted pressure taps in the same locations. Frequency based (spectral) analysis was carried out on the fluctuating pressure signal. It was found that the regions of flow separation coincide with the regions of maximum fluctuating pressure.

The paper presents experimental analysis of the airflow around the differential center housing of a rear drive full-scale passenger car. The study included investigation of local airflow total and static pressure, as well as surface flow visualization. Estimation of the local airflow velocity is based on the measured pressure coefficients. The experiments were carried out at different test facilities: in a climatic wind tunnel, in a full-scale wind tunnel and on-road. Influence of side wind was modeled by the yawing of the car in the full-scale wind tunnel. The results show the asymmetrical structure of the flow in both, vertical and horizontal planes. Estimated longitudinal relative local velocity decreases from maximum Vr ≈ 0.4 at the lower surface of the center housing, to about Vr ≈ 0 above the upper surface. Side wind increases airflow velocity around the center housing within the investigated yaw range ± 20°

A pressure-based technique has been developed for the purpose of radiator cooling airflow measurement. The technique was effectively utilised to quantify the local time-averaged air velocity through radiator cores in a small wind tunnel. The pressure difference indicated by the technique was found to be a function of the normal component of the air velocity. This paper describes the development and use of the technique which is compact, robust and non-intrusive. By applying this technique, the airflow distribution across the radiator face has been measured for a complete vehicle in an aerodynamic wind tunnel and in an environmental chamber. Results are compared for the different test environments. The influence of airflow distribution on the Specific Dissipation (a parameter used for evaluating radiator cooling performance) is examined and results for propeller-based methods and pressure-based methods are compared.

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.

The paper considers a novel waste heat recovery (WHR) system integrated with the engine architecture in a hybrid electric vehicle (HEV) platform. The novel WHR system uses water as the working media and recovers both the internal combustion engine coolant and exhaust energy in a single loop. Results of preliminary simulations show a 6% better fuel economy over the cold start UDDS cycle only considering the better fuel usage with the WHR after the quicker warm-up but neglecting the reduced friction losses for the warmer temperatures over the full cycle.

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.

Engine cooling systems are usually designed to meet two rare and extreme conditions; driving at maximum speed and driving up a specified gradient at full throttle while towing a trailer of maximum permitted mass. At all other times, the cooling system operates below its maximum capacity with an incurred drag penalty. In this work it is being suggested to design the system using the existing methods and then vary the area of the cooling air intakes to permit the minimum amount of cooling air for adequate engine cooling. A full-size, Australian made Ford Falcon car (a large modern 'family' saloon) was tested at the Monash University Aero-acoustic Wind Tunnel. The cooling air intakes of the vehicle were shielded progressively until fully blocked. Four different possibilities of shielding were investigated with the aim of determining the variation of drag reduction with the shielding method employed.

For high-speed driving conditions, the air flow around a car creates wind noise that is transmitted into the cabin, which can dominate other noises. If an atmospheric wind is present, it will create a turbulent cross wind, which not only changes the air flow velocity and direction as experienced by the vehicle, but leads to continuously varying wind noise, as heard inside the car. The purpose of this paper is to look at how the on-road wind environment affects wind noise, and to evaluate the need to simulate real on-road conditions such as fluctuating yaw angles and velocities in vehicle wind tunnels.

The sensitivity of cross-winds in reducing the engine cooling ability in motor cars is highlighted. Tests on three different motor cars were conducted in the Monash University full-scale wind tunnel at different yaw angles under different wind velocities. The test results show that motor car engine cooling capability decreases with an increase in yaw angles. For a wind velocity of 14 m/s, a 13% decrease in radiator cooling capability was found at a yaw angle of 20° compared to a zero yaw angle. The effect of yaw angles on the engine cooling also depends on the motor car front-end configuration, but this becomes less important with increasing wind velocity. The effect of cross-winds on car engine cooling was also evaluated by on-road engine cooling tests. A convenient experimental method to measure wind velocity and yaw angle relative to a moving car is also described.

Wind noise sources are described including those from the A-pillar region, cavities and bluff bodies. Hydrodynamic pressure fluctuations results from flow separations (in such areas as the A-pillars and mirrors) that generate relatively broad band in-cabin noise. The influence on local radii of the A-pillar is outlined and shown to be a dominant factor in determining hydrodynamic pressure fluctuations in the side-glass regions. Small cavities (eg. styling or water management channels on the mirror casing) generate high-frequency acoustic tones that can also be heard in the cabin and an example of tones from a whistling mirror cavity is shown. A spectrogram of in-cabin noise obtained whilst driving in strong winds is used to illustrate the variability of noise that can be heard on-road and to consider the influence of the relative wind speed.

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).

In this paper, a theoretical model for the calculation of Specific Dissipation (SD) was developed. Based on the model, the effect of ambient and coolant radiator inlet temperatures on SD has been predicted. Results indicate that the effect of ambient and coolant inlet temperature variation on SD is small (less than 2%) when ambient temperature varies between 10 and 50°C and coolant radiator inlet temperature between 60 and 120°C. The effect of coolant flowrate on SD is larger if there is a larger flowrate variation. Experimental results indicate that a 1 % variation at 1.0 L/s will cause about ±0.6% SD variation. Therefore the flowrate should be carefully controlled.