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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.

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.

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.

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.

This paper summarises the effects of turbulence on the aerodynamics of road vehicles, including effects on forces and aero-acoustics. Data are presented showing that a different design of some vehicles may result when turbulent flow is employed. Methods for generating turbulence, focusing on physical testing in full-size wind tunnels, are discussed. The paper is Part Two of a review of turbulence and road vehicles. Part One (Cooper and Watkins, 2007) summarised the sources and nature of the turbulence experienced by surface vehicles.

Noise and vibration have an important influence on a customer's perception of vehicle quality and cabin interior noise levels are a key criteria. The interior sound levels of automobiles have been significantly reduced over the years, with reductions in power train, tire and external wind noise. One of the highest in-cabin noise levels now arises from heating, ventilating and air conditioning systems, generated by the air-rush noise at various HVAC settings. Thus quieter climate control systems are desired by car manufacturers. A systematic benchmarking study was performed to investigate the in-cabin noise of vehicles. 21 passenger cars including compact, mid-size, full-size, and a truck were selected. Tests were conducted on relatively new production vehicles in various conditions. A binaural head system was used in front passenger seat to measure noise levels. The methodology used and the experimental results were presented in this paper.

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.

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.

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.

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.

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.

Water tow-tank tests were performed for the Ahmed model at a range of “high-drag” backlight angles at Reynolds numbers of up to 1.3 × 105. Dye was injected just upstream of the c-pillars and visualizations were recorded with a submerged CCD camera moving with the model. Discrete sub-vortices were found to be shed periodically along the length of the c-pillar at Strouhal numbers (based on square root of frontal area) between 8 and 12. These sub-vortices were observed to undergo vortex pairing and then to roll up into the familiar c-pillar vortices. These observations are consistent with previously published observations for delta wings. Wind tunnel tests were performed in order to provide Reynolds numbers of up to 1.6 × 106. These revealed some spectral features which could be due to the shedding and pairing of discrete vortices from the c-pillar but the evidence was much less conclusive than at low Reynolds number.

Two domains of aerodynamic testing of vehicles are identified; one representing typical driving conditions, where the average atmospheric wind is less than about 10 m/s; the other representing driving under extreme wind conditions for safety considerations. The first domain influences fuel consumption and other parameters related to driving comfort (e.g. aerodynamic noise, transient forces and transient moments experienced during general driving), whereas the second needs to be assessed for stability considerations. The purpose of this paper is to document turbulence commonly encountered by vehicles moving at highway speeds under typical driving conditions. In order to document this, data obtained from hot-wire anemometers fitted above a moving vehicle are presented. It was found that longitudinal and lateral turbulence intensities ranged between 2.5% to 5% and 2.0% to 10% respectively.

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.

This paper presents an experimental comparison between two factors used for evaluating engine cooling in motor cars, Air-to-Boil (ATB) and Specific Dissipation (SD). It is shown that Specific Dissipation can increase the experimental productivity for evaluating cooling system by giving more reliable results than Air-to-Boil. Results from road tests and experiments conducted in three different wind tunnels are presented. All experimental results indicate that Specific Dissipation gives more repeatable results and can be used in both stable and slowly-varying test conditions.