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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.

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.

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.

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.

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.

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.

A small-scale aeroacoustic wind tunnel has been designed and built to investigate tonal cavity noise in the frequency range applicable to passenger vehicles; 1 - 16 kHz. The tunnel is required for testing associated with an investigation into tonal cavity noise on passenger-vehicle wing mirrors. It was designed to operate in the low subsonic speed range (60 - 140 km/h) with a nozzle exit cross-sectional area of 0.02 m2 and a 4:1 aspect ratio. The design was intended to achieve a smooth, quiet flow facility. In this paper the design process is summarised and the factors leading to particular design decisions are detailed. An initial evaluation has shown that only minimal changes are required to achieve very smooth, even flow at the nozzle exit at all required test speeds. The acoustic design needs further work as there is a significant amount of flow noise at the nozzle exit between 1 and 13 kHz.