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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.

For the modern Formula 1 racing car, the degradation in aerodynamic performance when following another car is well documented. The problem can be broken into two parts; firstly the wake flow generated by these vehicles and the subsequent interaction a following car has with this field. Previous research [1, 2 & 3] has focused upon investigating the later without completely characterizing the former. This paper seeks to address this deficiency with initial data from a newly commissioned 30% scale Formula One wind tunnel model built to the 2011 technical regulations. Experimentation was carried out in the Industrial Wind-Tunnel (IWT) at RMIT University. In the absence of a rolling road an elevated ground plane was implemented; the results obtained show good agreement with the limited published material available. Using a high frequency response, four-hole pressure probe the aft body flow was investigated at multiple downstream locations.

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°

Wind tunnels which are large enough for full-scale trucks are rare, and the cost of satisfactorily-detailed models for smaller tunnels is high. The work presented shows the results from the application of a method which provides an over-the-road evaluation of the incremental changes in fuel consumption and drag coefficient produced following the addition of a variety of aerodynamic drag reducing devices to a tractor-trailer truck combination. The devices tested were an aerodynamic sunvisor, a roof-mounted air deflector, cab extenders, cab skirts, a trailer nose fairing, a set of trailer quads (quarter-rounds), and trailer skirts which were mounted on a low-forward-entry tractor and high box-van trailer. The significant differences between the wind tunnel and on-road drag reductions suggest that the effects of on-road wind turbulence can substantially reduce the wind tunnel results even though a 1.5% turbulence intensity level was used in the tunnel experiments.

Smart material is a suitable candidate for adaptive airfoil design as it can be customized to generate a specific response to a combination of inputs. Shape memory alloy (SMA) in particular is lightweight, produces high force and large deflection which makes it a suitable candidate for actuator in the adaptive airfoil design. By attaching SMA wires inside the airfoil, they can be activated to alter the shape of the airfoil. Placement of the actuator is crucial in obtaining the desired change of the airfoil camber. This paper proposed a design for the morphing wing aimed at changing the camber of the airfoil during cruise in order to increase the lift-to-drag ratio. Finite Element Method (FEM) analysis predicted the deformed airfoil geometry when the SMA wires were fully actuated. Numerical results are presented along with issues related to the fabrication of the morphing wing and implementation of the SMA actuator.

A morphing ram-air intake, capable of deploying from a flat, closed surface to an open state is investigated. Via geometric and material optimisation, an origami-inspired folding structure is developed to exhibit bi-stable behaviour. An iterative finite element design process was conducted, noting the effects of the critical design properties of geometry, bending stiffness and material strain limits on bi-stability and the achievable geometric shape change. As a first step, thermoplastic polyurethane elastomer materials are proposed while increased stiffness by fibre reinforcements are considered at a later design stage and evaluated under aerodynamic loading. The bi-stable structure is capable of remaining in either open or closed stable configurations without sustained actuation. The ability to retract the intake when not required has the potential to reduce drag. It is envisioned that such a concept may be readily adopted within automotive and aerospace applications.

The design of the exterior body shape and structure of a solar-electric sports car which competed in the 2019 Bridgestone World Solar Challenge (BWSC) Cruiser Class is explored. A low-drag and low-lift aerodynamic shape with a coefficient of lift near zero and drag area of 0.16 m2 is developed as a primary focus around the constraints of a solar array, occupant space, and aesthetics. The maximally sized 5 m2 rearward tilted solar array capable of generating an expected event average power of 885 W influences the size and shape of the roof. The space for which two occupants are seated in the vehicle is developed to achieve a reclined occupant position that minimizes the vehicle frontal area. A carbon fiber-reinforced polymer (CFRP) and foam composite sandwich monocoque make up the structure of the vehicle at a mass of 59.53 kg. Factors of practicality and their compromises are also explored.

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.

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.

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.

Noise and vibration have important influence on customer's perception of vehicle quality. Research and development have been conducted to investigate the vehicle Heating, Ventilation and Air Conditioning (HVAC) noise generation and transmission mechanism. Noise and vibration comparison tests have been completed for the proposed refinement solutions. Testing results are discussed paying special attentions to the air borne noise reduction. One of interior noise major contributors is the HVAC system, as air handling unit of the HVAC system is located behind the vehicle instrument panel within the cabin. Modifications made to internal structural geometry of the system have been conducted to provide insight into the effect of each structural feature on the overall Sound Pressure Level (SPL) and frequency spectrum components.

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.

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.

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.

Vortices formed around the A-pillar region dictates the pressure distribution on the side panels of a passenger vehicle and also can lead to aerodynamic noise generation. This paper compares the suitability of various turbulence models in simulating the flow behind a vehicle A-pillar region under laboratory operating conditions. Commercial software's (FLUENT and SWIFT) were used to compare the performance of various turbulence models. In FLUENT, a simplified vehicle model with slanted A-pillar geometry was generated using GAMBIT and in SWIFT, the simplified vehicle model was generated using Fame Hybrid. Computational Fluid Dynamics (CFD) simulations were carried out using FLUENT under steady state conditions using various turbulence models (k-, k- Realize, k- RNG, k- and Spalart Allamaras). In SWIFT, k-, A-RSM and HTM2 turbulence models were used for the steady state simulations. Investigations were carried out at velocities of 60, 100 and 140km/h and at 0-degree yaw angle.

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.

As open-wheeled racing cars frequently race in close proximity, a limiting factor on the ability to overtake is the aerodynamic performance of the vehicle while operating in a leading car's wake. Whilst various studies have examined the effectiveness of wings operating in turbulent flow, there has been limited research undertaken on the aerodynamic effect of such conditions on wheels. This study describes the influence of upstream turbulence on the wake flow features of an isolated wheel, since the flow field of a wheel will generally be turbulent (due to the wakes of upstream cars and/or bodywork). Pressure distributions and velocity vector plots are examined, which were obtained using a four-hole pressure-sensitive Cobra probe on a traverse 2.5 diameters downstream of the wheel axle line, in smooth and turbulent flow.

In this study, flow measurements were taken in the wake of a 3/10 scale model of a passenger vehicle using a high frequency, four-hole pressure probe (Dynamic Cobra Probe). The purposes of this study were to further the understanding of the wake development of a passenger vehicle in isolation (in order to provide representative input boundary conditions for CFD and EFD simulations of vehicles traveling in traffic) and to also investigate the wake properties under the influence of upstream turbulence (i.e. with a turbulence generator upstream). The results from several downstream planes are presented and include the time-averaged contour plots of turbulence intensity, velocity deficit and vorticity and cross-flow velocity fields. The presence of increased levels of upstream turbulence mostly affected the upper region of the vehicle wake. In this region, the A-pillar vortex was reduced in size and strength, while the C-pillar vortex had increased in both respects.