Development and Analysis-Driven Optimization of Superelastic Slat-Cove Fillers for Airframe Noise Reduction

Airframe noise constitutes a significant component of the total noise generated by transport aircraft during low-speed maneuvers, such as approach and landing; the leading-edge slat is a major source. Previous work has shown that the noise produced by the slat can be mitigated through the use of a slat-cove filler. Results from the initial prototype testing led to slat-cove filler concepts that incorporated a segmented structure and superelastic shape-memory alloy materials. A finite-element analysis model, based on the physical prototypes (with a shape profile optimized for maximum noise reduction), was created and used to analyze the slat-cove filler response to aerodynamic and slat retraction loads with the goal of optimization. The objective was minimization of the actuation force needed to retract the slat/slat-cove filler assembly subject to constraints that involved aeroelastic deflection of the slat-cove filler when deployed, maximum stress in the shape-memory alloy flexures, and the required ability of the slat-cove filler to deploy autonomously during slat deployment. The design variables considered included shape-memory alloy flexure thicknesses and lengths of various slat-cove filler components. Design of experiment studies were conducted and used to guide the subsequent optimization. From the optimization, it was found that a monolithic shape-memory alloy slat-cove filler minimized the actuation force while satisfying design constraints, which was consistent with prototype testing results.