Psychoacoustics of Flow-Induced Cabin Noise

Research Project, 2019

Background

A quiet cabin environment is a common concern of automotive and aeronautic industries to manufacture high-class productions in consideration of comfort. Besides, long-term exposure to a noisy environment might render health problems, e.g., psychological disorder and hearing loss. Turbulent flows are known as an important contributor to interior noise in truck cabins at cruising speeds between 80 and 90 kph. Besides, the flow-induced interior noise is more significant for trucks with hybrid and full electric propulsion systems,
where another noticeable noise contributor – engines -- is either absent or it is small and quite. The flow-induced interior noise for vehicles is mainly generated due to vibration of glass windows. The exterior turbulence and noise induced by side-view mirrors and A-pillars play important roles in exciting the vibration. Since the characteristics of turbulent flows are known to be dependent on bluff body geometries, a small geometrical modification/redesign of mirrors or A-pillars could change the cabin noise completely. Even though the same total noise level can be obtained between the original and redesigned mirrors and A-pillars, different levels at frequency bands might lead to completely different experiences for drivers or passengers. However, there are few studies in the literature on the
psychological impact of this particular noise. Previous studies with for instance car noise and air-craft noise show a strong influence of vibrations on sound perception describing the noise as not pleasent, undesirable, rough and attention demanding.

Objectives

A study will be initiated to establish a systematic method that connects the flow and noise simulation to the psychological evaluation.The noise sources induced by side-view mirrors will be identified according to spectral characteristics. The dominantly harmful/disturbing frequencies of the noise will be addressed. Perceptions and judgements of the noise will be assessed with a self-report instrument that we will develop.

Implementation/research approach

A numerical method, which couples the simulation of flows and noise, will be used to predict the cabin noise for three cases: two side-view mirrors mounted on a full-scale truck, and the truck without a mirror. A high-fidelity computational fluid dynamics (CFD) method, detached eddy simulation (DES), is employed in the flow simulation, and a finite-element method (FEM) in the noise simulation. The simulated noise signals will be converted to audio files using a post-processing tool, which is programmed with Matlab. The simulated noise signals and audio files will be analyzed to assess their acoustical impact on psychological health. In addition to the judgements
of the noise, additional scales assessing cognitive impairment and stress will be related to the different audio files.