An experimental study on the sound transmission loss of dissimilar fuselage sandwich panels of turbojet aircraft

Abstract

The analysis of acoustic performance of sandwich panels, designed explicitly for fuselage sidewalls of turbojet aircraft, has been revisited numerous times. However, the layouts and the sound transmission loss of the airborne fuselage sandwich panels have not been made available for public release. Against this idiosyncratic practice, this study envisioned disseminating the know-how on the sound attenuation ability of dissimilar sandwich panels implemented in the fuselage of turbojet aircraft. To efficiently absorb and dampen the acoustic energy, the sandwich panels were systematically configured using a honeycomb core, felts and a closed cell aluminum-foam in the material lay-up. The face sheets of the sandwich panels were composed of either glass fiber-reinforced epoxy or carbon fiber-reinforced epoxy composites. The sandwich panels were tested as acoustic barriers to a diffuse sound field in a sound transmission suite consisting of two adjacent sound reverberation rooms. As found, a rubber damping layer in the material lay-up of a sandwich panel reinforced the sound transmission loss at frequencies beyond 500 Hz. Multiple felts augmented the sound transmission loss in the frequency regime beyond 315 Hz. The panel edges needed to be sealed properly to reproduce the sound transmission loss of a sandwich panel in successive experiments. This study leveraged many-faceted insights into the configuration (constituent materials, number of material layers, thickness, and stacking sequence) of commercially feasible sandwich panels. Besides, this study proposed optimized sandwich configurations based on the sound transmission loss, which will help aircraft manufacturers to apply these sandwich panels without further modifications.