Analysis of the boundary layer noise transmitted through aircraft sidewalls

TLDR: In this paper, the results of a study concerned with the prediction of the airflow noise transmitted through an element of the fuselage structure: a double panel of finite extent which consists of a pair of thin elastic plates, containing a light insulating material separated from the inner skin by an air gap.

Abstract: In this paper, the results are presented of a study concerned with the prediction of the airflow noise transmitted through an element of the fuselage structure: a double panel of finite extent which consists of a pair of thin elastic plates, containing a light insulating material separated from the inner skin by an air gap. This configuration is representativ e of typical compound sidewalls in large commercial aircraft. A solution based on modal coupling is obtained and validated by comparisons with other solutions on various test cases. A physical interpretation is given for the calculated vibro-acoustic response of a double partition system excited by a turbulent boundary layer, and the effect of an air gap between the insulation facing bag and the trim panel is analysed. It is shown that the levels of the inwardly radiated sound power are mainly determined by the contribution of the first skin panel-controlled mode and the added damping effect due to the insulating material has little effect below this resonance. In order to achieve sound reduction in the very low frequency domain, the performance of various active control strategies are examined and compared. It is found that the most efficient strategy is the suppression of the low order skin panel structural modes. However, we note that significant reductions in the sound power radiated can also be achieved by the active suppression of the low order structural modes of the trim panel.