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Wind noise is a significant source of interior noise in automobiles at cruising conditions, potentially creating dissatisfaction with vehicle quality. While wind noise contributions at higher frequencies usually originate with transmission through greenhouse panels and sealing, the contribution coming from the underbody area often dominates the interior noise spectrum at lower frequencies. Continued pressure to reduce fuel consumption in new designs is causing more emphasis on aerodynamic performance, to reduce drag by careful management of underbody airflow at cruise. Simulation of this airflow by Computational Fluid Dynamics (CFD) tools allows early optimization of underbody shapes before expensive hardware prototypes are feasible. By combining unsteady CFD-predicted loads on the underbody panels with a structural acoustic model of the vehicle, underbody wind noise transmission could be considered in the early design phases.

The object of the validation study presented in this paper is a generic vehicle, the so-called SAE body, developed by a consortium of German car manufacturers (Audi, Daimler, Porsche, Volkswagen). Many experiments have been performed by the abovementioned consortium on this object in the past to investigate its behavior when exposed to fluid flow. Some of these experiments were used to validate the simulation results discussed in the present paper. It is demonstrated that the simulation of the exterior flow is able to represent the transient hydrodynamic structures and at the same time both the generation of the acoustic sources and the propagation of the acoustic waves. Performing wave number filtering allows to identify the acoustic phenomena and separate them from the hydrodynamic effects. In a next step, the noise transferred to the interior of the cabin through the glass panel was calculated, using a Statistical Energy Analysis approach.

Exhaust and muffler noise is a challenging problem in the transport industry. While the main purpose of the system is to reduce the intensity of the acoustic pulses originating from the engine exhaust valves, the back pressure induced by these systems must be kept to a minimum to guarantee maximum performance of the engine. Emitted noise levels have to ensure comfort of the passengers and must respect community noise regulations. In addition, the exhaust noise plays an important role in the brand image of vehicles, especially with sports car where it must be tuned to be “musical”. However, to achieve such performances, muffler and exhaust designs have become quite complex, often leading to the rise of undesired self-induced noise. Traditional purely acoustic solvers, like Boundary Element Methods (BEM), have been applied quite successfully to achieve the required acoustic tuning.

For most car manufacturers, aerodynamic noise is becoming the dominant high frequency noise source (> 500 Hz) at highway speeds. Design optimization and early detection of issues related to aeroacoustics remain mainly an experimental art implying high cost prototypes, expensive wind tunnel sessions, and potentially late design changes. To reduce the associated costs as well as development times, there is strong motivation for the development of a reliable numerical prediction capability. The goal of this paper is to present a computational approach developed to predict the greenhouse windnoise contribution to the interior noise heard by the vehicle passengers. This method is based on coupling an unsteady Computational Fluid Dynamics (CFD) solver for the windnoise excitation to a Statistical Energy Analysis (SEA) solver for the structural acoustic behavior.

In the past years, Eberspaecher has developed active exhaust silencers for several passenger vehicles with different engines on a prototype level. In general, a substantial reduction of the exhaust noise is regularly achieved in a frequency range of 40 - 400 Hz covering the most relevant engine orders. In exhaust system development the main design conflicts are noise reduction, silencer volume/weight and backpressure. Recent progress was made in the development of the durability and industrialization of the actuator. This component could be reduced in size and weight thus allowing the integration in different design spaces of many vehicles. In some cases, the conventional dual exhaust system can even be replaced by an active single exhaust line without compromising on the acoustic or backpressure targets but saving > 50 % of space and > 30% weight. The potential impact of this technology on future vehicle designs will be discussed.

Over the past few years, the measurement procedure for the pass-by noise emission of vehicles was changed and new limit values have been set by the European Parliament which will come into force within the next few years. Moreover, also the limits for chemical emissions such as NOx, particulates and CO2 have been lowered dramatically and will continue to be lowered according to a roadmap decided not only in Europe but also in other markets throughout the world. This will have an enormous impact on the design of future passenger cars and in particular on their powertrains. Downsizing, downspeeding, forced induction, and hybridization are among the most common general technology trends to keep up with these challenges. However, most of these fuel saving and cleaner technologies also have negative acoustic side effects.

Over the past decades, interior noise from wind noise or engine noise have been significantly reduced by leveraging improvements of both the overall vehicle design and of sound package. Consequently, noise sources originating from HVAC systems (Heat Ventilation and Air Conditioning), fans or exhaust systems are becoming more relevant for perceived quality and passenger comfort. This study focuses on HVAC systems and discusses a Flow-Induced Noise Detection Contributions (FIND Contributions) numerical method enabling the identification of the flow-induced noise sources inside and around HVAC systems. This methodology is based on the post-processing of unsteady flow results obtained using Lattice Boltzmann based Method (LBM) Computational Fluid Dynamics (CFD) simulations combined with LBM-simulated Acoustic Transfer Functions (ATF) between the position of the sources inside the system and the passenger’s ears.

Developing a low interior noise level of vehicles is a big challenge - even a greater one if one thinks about aeroacoustics. Aeroacoustic noise and its origins are usually identified with the help of prototypes when exterior design changes or the replacement of exterior parts like side mirrors are very limited. However, computational aeroacoustic (CAA) methods in virtual project phases offer more design options for the vehicle's geometric shape. The early consideration of aeroacoustic relevant design changes helps to keep project costs low by avoiding tool changes. This paper describes MAGNA STEYR's virtual aeroacoustic process starting from standardized model generation and simulation of wind noise, including the validation of computational results via comparison with measurement data gathered in an acoustic wind tunnel. The simulations are carried out using the commercial CAA code “PowerFLOW” (Exa) based on the Lattice-Boltzmann method.

In the past years Eberspaecher has installed Active Exhaust Silencers on several passenger vehicles with different diesel and gasoline engines on a prototype level. Meanwhile, a substantial reduction of the exhaust noise is regularly achieved in a broad frequency range covering all relevant engine orders. Due to the higher acoustic excitation and higher exhaust temperatures in gasoline engines it is more difficult to implement the ANC-technology on those engines. However, results from roller test benches focus on the acoustic performance as well as weight and volume reductions and demonstrate a marked improvement which was achieved with gasoline engines too. Further progress was made in the development of the durability and industrialization of all relevant components of the system. Finally, current design trends and possible fields of application will be discussed.

Wind noise has become an important indicator for passenger automobile quality. Several transmission paths can be related to different parts of the vehicle exterior. While the greenhouse (side glasses, windshield, seals & others) often dominates the interior noise level above 500 Hz, the contribution coming from the underbody area usually dominates the interior noise spectrum at lower frequencies. This paper describes a framework of numerical tools which is capable of determining realistic underbody turbulent and acoustic loads being generated for typical driving conditions, as well as performing the noise transmission through underbody panels and the propagation of sound to the drivers ear location.

In all major markets, the legislation on emissions (CO2, NOx, and PM) and on pass-by noise limits have been drastically lowered over the last years and will be even lower in the near future. This will have an enormous impact on the design of future passenger cars, their powertrains, and finally their exhaust systems with an inherent cost penalty. Moreover, the individual market requirements in Europe, Asia and the Americas differ in some respect often calling for individual variants. The increasing number of vehicle models and platform derivatives e.g. sedan, hatchback, coupe, convertible, sports utility vehicle, cross-over etc. leads to a huge variety of exhaust systems even within a single OEM platform let alone a whole OEM product portfolio. This causes significant effort in development, tooling, manufacturing, part handling, and logistics. The Active Noise Cancellation technology (ANC) has been investigated in the automotive industry for many years.

This paper presents an approach to numerically simulate greenhouse windnoise. The term “greenhouse windnoise” here describes the sound transferred to the interior through the glass panels of a series vehicle. Different panels, e.g. the windshield or sideglass, are contributing to the overall noise level. Attached parts as mirrors or wipers are affecting the flow around the vehicle and thus the pressure fluctuations which are acting as loads onto the panels. Especially the wiper influence and the effect of different wiper positions onto the windshield contribution is examined and set in context with the overall noise levels and other contributors. In addition, the effect of different flow yaw angles on the windnoise level in general and the wiper contributions in particular are demonstrated. As computational aeroacoustics requires accurate, highly resolved simulation of transient and compressible flow, a Lattice-Boltzmann approach is used.

The pass-by noise limits of passenger vehicles according to ISO 362 / R51.03 [1, 2] will be further reduced by 2 dB in 2024 in Europe. Since the pass-by noise is substantially influenced by exhaust noise, the effort for the exhaust system needs to be increased substantially. This results in systems with larger mufflers or higher backpressure. However, the more stringent CO2-emission targets require ever more efficient powertrains, which calls for rather lower backpressure to optimize the engine design. This paper describes how compact active exhaust lines can support a design for low backpressure and high acoustic attenuation at the same time. For two passenger vehicles with gasoline engines active exhaust lines are investigated in detail and the results are compared to the series production exhaust lines. Thus, in one exemplary case, the pass-by noise of a limousine could be reduced from 70 dB(A) to 68 dB(A) without any change in the vehicle design except the improved exhaust system.