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Item type:Publication, Access status: without files , Impact of surface roughness on acoustic resonators made of closed-cell lightweight foams(Curran Associates, Inc., 2021-07); ; ; ; Acoustic resonators, such as Helmholtz resonators or slit resonators, are known as a highly efficient noise control mean for narrow frequency band applications. Their simple passive structure can be built from many different materials. If a noise control treatment is highly restricted by the additional weight, those resonators could be built out of a closed-cell lightweight foam. Because of both, manufacturing reasons and the cellular microstructure of the foam, the surface of such resonators is not perfectly smooth. Especially when openings of the resonators are milled in the foam, the surface roughness inside the opening might be relatively high. This leads to a certain damped behavior of the resonator that cannot be captured by current models. In this contribution, the effect of surface roughness on the airflow resistance and its impact on the acoustic behavior of slit resonators, like the absorption coefficient or the transmission loss for wall integrated means, is studied experimentally.Publicationtype: Conference Paper58 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Aircraft side wall with improved low-frequency sound insulation using a lining panel with Helmholtz resonators(International Institute of Acoustics and Vibration (IIAV), 2019); ; ; The continuous development of aircraft engines aims to reduce fuel consumption by increasing the bypass ratio. However, an increased bypass ratio changes the sound emission of the engine, such that the sound spectrum inside the cabin can be dominated by low frequency tones with high sound pressure levels, penetrating more efficiently the current cabin wall than sound of higher frequencies. Thus, the comfort level of the passengers could be adversely affected. This contribution presents a new side wall panel design that is capable to significantly increase the transmission loss of low frequency tones. The rear side of the lining is fully covered by a resonator system of a cantilever integrated into a Helmholtz resonator. With this approach, the lining with resonators can be tuned with respect to two resonance frequencies to improve the sound transmission loss of the cabin wall. A transfer matrix for the Helmholtz resonator panel is derived and the transmission loss of the proposed side wall design is determined. The analytically calculated transmission loss is compared to numerical and experimental results obtained under diffuse field conditionsPublicationtype: Conference Paper145