New designs of sandwich panels to mitigate high-frequency noise inside space vehicles

Abstract

Radiation of noise to the interior of a space vehicle during liftoff and transonic climb is a long-standing problem. To attenuate noise inside the crew compartment during launch and in-space operation, sandwich panels have been employed in the pressurized outer shell to passively reduce the exterior noise transmission. However, the layouts and the sound transmission loss of the implemented 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. To efficiently absorb and dampen the acoustic energy, the sandwich panels were specifically configured using a honeycomb core, felts and a closed cell aluminum-foam in the material lay-up. The face sheets of the sandwich panels consisted 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. As found, an increase in the panel thickness brought a decrease in the anti-symmetric coincidence frequency of sandwich panels. A rubber damping layer in the material lay-up added limp mass to a sandwich panel and reduced the panel vibration at excitation frequencies beyond 500 Hz. Multiple felts reinforced the sound transmission loss of a sandwich panel by dissipating the acoustic energy into thermal energy at the felt interstices in the frequency regime beyond 315 Hz. In conclusion, this study proposed optimized sandwich configurations considering the constitutive materials, number of material layers, material layer thickness and stacking sequence. The optimized sandwich configurations could fairly deliver the demanded sound transmission loss in the high-frequency regime.