Design and Optimization of a Morphing Slat Gap Filler for Aircraft Noise Reduction Including Aerodynamic Visualization Approaches

Abstract

A slat gap filler (SGF) is a structure that spans the gap between the leading edge of the wing and slat on a transportation category aircraft. This structure has potential to reduce airframe noise on approach to landing when aircraft are often flying over densely populated areas. Previous experimental aerodynamic studies showed a variety of SGF geometries can cause noise reduction. This design study expands on previous work to determine an optimal noise reducing SGF structure.

Nonlinear structural analysis of three morphing SGF design concepts explores the potential design space. The structure requires the facilitation of geometry changes between the deployed and retracted slat states, and the practical capability to stow the structure from flow for an emergency, high angle-of-attack maneuver. Because of these operational necessities, shape memory alloys (SMAs) are chosen as the SGF material. For all concepts, the structure is modeled using a superelastic SMA material exhibiting hysteretic behavior. Each concept is defined by its external or internal wing attachment location, and by its stowing method: automatic via a stress-bias or mechanical via connector actuators. The suitability of the three concepts is tested within an experimental design framework against four separate design variables per concept.

Results from the exploration are utilized to select a single SGF concept. Fluid dynamics simulations are used as inputs to an aeroacoustic formulation to determine overall noise for an SGF configuration. An efficient global optimization (EGO) strategy is implemented with the structural and aeroacoustic solvers. The structural side of the optimization considers the objectives of mass and actuation force along with structural constraints. The acoustic side of the optimization considers an objective to minimize noise. Together, these objectives are used to determine an optimal SGF configuration.

This SGF was designed to facilitate an experimental testing campaign. However, it was difficult to demonstrate the features and identify the flaws of a 3-dimensional design using conventional 2-dimensional graphic displays. A novel mixed reality toolkit was developed to visualize complex results in the experimental facility to assist in research and educational discussions.