Design of Shape-Adaptive Deployable Slat-Cove Filler for Airframe Noise Reduction

Abstract

Mechanical instabilities and elastic nonlinearities are emerging means for designing deployable and shape adaptive structures. Dynamic snap-through buckling is investigated here as a means to tailor the deployment and retraction of a slat-cove filler (SCF), a morphing component used to reduce airframe noise. Upon deployment, leading-edge slats create a cove between themselves and the main wing, producing unsteady flow features that are a significant source of airframe noise. A SCF is designed here to autonomously snap out as the slat deploys, providing a smoother aerodynamic profile that reduces flow unsteadiness. The nonlinear structural behavior of the SCF is studied, and then tailored, to achieve a desirable snapping response. Three SCF configurations are considered: 1) a constant thickness (monolithic) superelastic shape-memory alloy (SMA) SCF, 2) a variable-thickness SMA SCF, and 3) a set of stiffness-tailored fiberglass composite SCFs. Results indicate that, although monolithic SMA SCFs provide a simple solution, thickness variations in both the SMA and stiffness-tailored composite SCF designs allow a decrease of the energy required for self-deployment and a reduction of the severity of the impact between the SCF and the slat during stowage. The enhanced nonlinear behavior from stiffness tailoring reduces peak material strains in comparison to previous SMA SCF designs that leveraged material superelasticity for shape adaptation. The stiffness tailoring is readily achieved through the use of layered composites, facilitating considerable weight savings compared to the dense SMA designs. The aeroelastic response of different SCFs is calculated using fluid/structure interaction analyses, and it is shown that both SMA and composite SCF designs can deploy and retract in full flow conditions.