ESI helps Bentley improve the aerodynamic performance of vehicles, making electric travel quieter

2024-01-22

Luxury car manufacturers are committed to providing users with a sound experience. Now, the automotive industry is shifting towards electrification, which has changed the acoustic environment. Without an internal combustion engine, it means that other sounds are more prominent (usually from air sources, even glass panels can emit noise). Acoustic designers are committed to predicting all potential noise sources, including their types, locations, and transmission pathways.

In order to quantify the sources and pathways of noise as early as possible in the development process, reduce the impact, and avoid costly design changes in the later stage, Bentley's acoustic engineers have been using computational methods to predict the internal acoustic noise of the entire vehicle in the new design. According to foreign media reports, in a joint study with ESI Group, Bentley hopes to develop a cost-effective method to predict the aerodynamic internal noise of the entire vehicle in the early development process, thereby reducing reliance on expensive physical prototypes.

A typical vehicle structure may generate up to 100000 modes (up to 8000Hz), as well as 250000 internal cavity modes, requiring millions of degrees of freedom to map the small wavelengths of these high-frequency bands. The team found that it was not possible to process such a large amount of data through deterministic methods to achieve a higher frequency audible range, so they turned to statistical methods. Due to the impact of high-frequency amplitude changes on the perception of automotive air acoustics, researchers have concluded that a combination of CFD and Statistical Energy Analysis (SEA) methods should be used.

SEA is a mature method that can be used to predict indoor noise and vibration, as well as develop sound and damping packages. By using the SEA module of the acoustic simulation software VA One (an improved version of the industry standard software AutoSEA2), it is possible to fully understand the energy flow around and inside the vehicle, thereby conducting various analyses. The external sound field consists of near-field and mid field cavities, which are discretized to consider diffraction effects. The cavity of the midfield is connected to a semi infinite fluid to represent the unbounded external acoustic space. After two CFD simulations, the team exported panel excitations to the acoustic simulation software VA One. Apply the spectral calculation of each panel to the vehicle SEA model based on the wavenumber frequency.

Researchers will compare the results of the simulation process with measurement data obtained in a full-scale aerodynamic wind tunnel at the Institute of Internal Combustion Engines and Vehicles (FKFS) at the University of Stuttgart. In this measurement process, the luxury Bentley sports car used was comparable to the model used for simulating the event; The wind tunnel moving belt system and the wheels of the vehicle are both in a stationary state, reflecting the CFD simulation results; The seals and "closed circuit" of the test vehicle are taped to eliminate potential air acoustic leaks caused by gaps in the vehicle's sealing system.

The testing team stated that the total internal noise predicted through CFD and SEA methods is very consistent with wind tunnel measurement results, providing options for simplifying testing and development phases in the future.

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