Elastomeric Structural Attachment Concepts for Aircraft Flap Noise Reduction - Challenges and Approaches to Hyperelastic Structural Modeling and Analysis

Abstract

Airframe noise is a significant part of the overall noise of transport aircraft during the approach and landing phases of flight. Airframe noise reduction is currently emphasized under the Environmentally Responsible Aviation (ERA) and Fixed Wing (FW) Project goals of NASA. A promising concept for trailing-edge-flap noise reduction is a flexible structural element or link that connects the side edges of the deployable flap to the adjacent main-wing structure. The proposed solution is distinguished by minimization of the span-wise extent of the structural link, thereby minimizing the aerodynamic load on the link structure at the expense of increased deformation requirement. Development of such a flexible structural link necessitated application of hyperelastic materials, atypical structural configurations and novel interface hardware. The resulting highly-deformable structural concept was termed the FLEXible Side Edge Link (FLEXSEL) concept. Prediction of atypical elastomeric deformation responses from detailed structural analysis was essential for evaluating feasible concepts that met the design constraints. The focus of this paper is to describe the many challenges encountered with hyperelastic finite element modeling and the nonlinear structural analysis of evolving FLEXSEL concepts. Detailed herein is the nonlinear analysis of FLEXSEL concepts that emerged during the project which include solid-section, foamcore, hollow, extended-span and pre-stressed concepts. Coupon-level analysis performed on elastomeric interface joints, which form a part of the FLEXSEL topology development, are also presented.

Experimental Study of Flexible Skin Designs Between a Moving Wing Segment and a Fixed Wing Part on a Full Scale Demonstrator

“…A wind tunnel experiment was done for this concept and shows a reduction of approximately 3dB over a wide frequency range for the deflected flap with gap cover compared to a flap without cover [13]. The work of Sreekantamurthy pick up the concept from Khorrami for simulation studies [14]. The elastomer skin with the hollow cores shows high skin strains of approximately 500 %.…”

Morphing elastically lofted transition for active camber control surfaces

“…It appears however, that the device tested was a non-straining elastomeric mockup of the desired shape. This is likely due to the difficulty that was experienced with designing a working version of this transition, [10] wherein the very high strain requirements of ~500% led to unacceptably high force requirements and difficulties designing appropriate fixtures. Attempts to reduce these forces by using the hollowed out configuration led to extensive wrinkling of the transition surface.…”