Incorporation of acoustic black hole stiffeners into composite airframes for reduction of noise radiation

Stiffened composite panels are commonly used in aerospace structures, because they are lightweight, while maintaining a high load-bearing ability. However, their high stiffness-to-mass ratio makes them efficient noise radiators. In rotorcraft cabins made with composite panels, for example, the internal noise levels can be quite high such that pilot and passenger communication and comfort are disrupted. This has led to a need for innovative noise reduction strategies for composite rotorcraft panels. A specialized stiffener, which incorporates the acoustic black hole (ABH) effect into the cross section, is proposed to improve the damping of stiffened composite panels. By incorporating the damping concept into the stiffeners, the panel’s radiated noise can be reduced while maintaining the weight advantages and panel strength. To determine the advantages and trade-offs of this concept, numerical models have been developed and incorporated into an optimization scheme. Computational studies reveal promising results from the optimized ABH stiffeners as compared to a baseline panel with traditional stiffeners.